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Cython Changelog

3.1.0 (2024-??-??)

Features added

  • Several improvements were made to reduce the size of the resulting extension modules. (Github issue 4425)
  • Function calls now use the PEP-590 Vectorcall protocol, even when passing keyword arguments. (Github issues 5804)
  • The Python int type now maps directly to PyLong and is inferred accordingly. (Github issue 4237)
  • Integer operations on known int types are faster. (Github issue 5785)
  • Many issues with the Limited C-API were resolved. (Github issues 5697, 5798, 5845, 5846, 5885, 5886, 5888)
  • Several issues with the gdb support were resolved. Patches by Kent Slaney. (Github issues 5955, 5948)
  • C++ classes implemented in Cython can now use method overloading. Patch by samaingw. (Github issue 3235)
  • Assigning a Python container to a C++ vector now makes use of __length_hint__ to avoid reallocations. Patch by Denis Lukianov. (Github issue 6077)
  • Dataclasses support the match_args option. (Github issue 5381)
  • Threading in parallel sections can now be disabled with a new use_threads_if condition. (Github issue 5919)
  • f-strings are slightly faster. (Github issue 5866)
  • dict.pop() is faster in some cases. (Github issue 5911)
  • Most builtin methods now provide their return type for type inference. (Github issues 4829, 5865)
  • .isprintable() is optimised for Unicode characters. (Github issue 3277)
  • The parser was updated for Unicode 15.1 (as provided by CPython 3.13a4).

Bugs fixed

  • Dataclasses did not handle default fields without init value correctly. (Github issue 5858)
  • Exception values were not always recognised as equal at compile time. (Github issue 5709)
  • Running Cython in different Python versions could generate slightly different C code due to differences in the builtins. (Github issue 5591)
  • The -a option in the IPython magic no longer copies the complete HTML document into the notebook but only a more reasonable content snippet. Patch by Min RK. (Github issue 5760)
  • Uselessly referring to C enums (not enum values) as Python objects is now rejected. Patch by Vyas Ramasubramani. (Github issue 5638)
  • Several C++ warnings about char* casts were resolved. (Github issues 5515, 5847)
  • C++ undefined behaviour was fixed in an error handling case. (Github issue 5278)
  • The PEP-479 implementation could raise a visible RuntimeError without a trace of the original StopIteration. (Github issue 5953)
  • Unterminated string literals could lock up the build in an infinite loop. (Github issue 5977)
  • Exporting C functions uses better platform compatible code. (Github issue 4683)

Other changes

  • Support for Python 2.7 - 3.6 was removed, along with large chunks of legacy code. (Github issue 2800)
  • The generated C code now requires a C99 compatible C compiler.
  • language_level=3 is now the default. language_level=3str has become a legacy alias. (Github issue 5827)
  • The previously shipped NumPy C-API declarations (cimport numpy) were removed. NumPy has been providing version specific declarations for several versions now. (Github issue 5842)
  • Usages of the outdated WITH_THREAD macro guard were removed. (Github issue 5812)
  • The options for showing the C code line in Python exception stack traces were cleaned up. Previously, disabling the option with the CYTHON_CLINE_IN_TRACEBACK macro did not reduce the code overhead of the feature, and the c_line_in_traceback compile option was partly redundant with the C macro switches and lead to warnings about unused code. Since this is considered mostly a debug feature, the new default is that it is _disabled to avoid code and runtime overhead. It can be enabled by setting the C macro to 1, and a new macro CYTHON_CLINE_IN_TRACEBACK_RUNTIME was added that controls the runtime configurable setting if the feature is enabled, which was previously only available through the compile option. The compile option is now deprecated (but still available), and users should migrate to using the two C macros only. (Github issue 6036)
  • Includes all fixes as of Cython 3.0.10 (but generates C99 code in some places).

3.0.10 (2024-03-30)

Bugs fixed

  • Cython generated incorrect self-casts when directly calling final methods of subtypes. Patch by Lisandro Dalcin. (Github issue 2747)
  • Internal C names generated from C function signatures could become too long for MSVC. (Github issue 6052)
  • The noexcept warnings could be misleading in some cases. Patch by Gonzalo Tornaría. (Github issue 6087)
  • The @cython.ufunc implementation could generate incomplete C code. (Github issue 6064)
  • The libcpp.complex declarations could result in incorrect C++ code. Patch by Raffi Enficiaud. (Github issue 6037)
  • Several tests were adapted to work with both NumPy 1.x and 2.0. Patch by Matti Picus. (Github issues 6076, 6100)
  • C compiler warnings when the freelist implementation is disabled (e.g. on PyPy) were fixed. It can now be disabled explicitly with the C macro guard CYTHON_USE_FREELISTS=0. (Github issue 6099)
  • Some C macro guards for feature flags were missing from the NOGIL Python configuration.
  • Some recently added builtins were unconditionally looked up at module import time (if used by user code) that weren't available on all Python versions and could thus fail the import.
  • A performance hint regarding exported pxd declarations was improved. (Github issue 6001)

3.0.9 (2024-03-05)

Features added

  • Assigning const values to non-const variables now issues a warning. (Github issue 5639)
  • Using noexcept on a function returning Python objects now issues a warning. (Github issue 5661)
  • Some C-API usage was updated for the upcoming CPython 3.13. Patches by Victor Stinner et al. (Github issues 6003, 6020)
  • The deprecated Py_UNICODE type is no longer used, unless required by user code. (Github issue 5982)
  • std::string.replace() declarations were added to libcpp.string. Patch by Kieran Geary. (Github issue 6037)

Bugs fixed

  • Cython generates incorrect (but harmless) self-casts when directly calling final methods of subtypes. Lacking a better solution, the errors that recent gcc versions produce have been silenced for the time being. Original patch by Michał Górny. (Github issue 2747)
  • Unused variable warnings about clineno were fixed when C lines in tracebacks are disabled. (Github issue 6035)
  • Subclass deallocation of extern classes could crash if the base class uses GC. Original patch by Jason Fried. (Github issue 5971)
  • Type checks for Python memoryview could use an invalid C function. Patch by Xenia Lu. (Github issue 5988)
  • Calling final fused functions could generate invalid C code. (Github issue 5989)
  • Declaring extern enums multiple times could generate invalid C code. (Github issue 5905)
  • pyximport used relative paths incorrectly. Patch by Stefano Rivera. (Github issue 5957)
  • Running Cython with globbing characters ([]*?) in the module search path could fail. Patch by eewanco. (Github issue 5942)
  • Literal strings that include braces could change the C code indentation.

Other changes

  • The "enum class not importable" warning is now only issued once per enum type. (Github issue 5941)

3.0.8 (2024-01-10)

Bugs fixed

  • Using const together with defined fused types could fail to compile. (Github issue 5230)
  • A "use after free" bug was fixed in parallel sections. (Github issue 5922)
  • Several types were not available as cython.* types in pure Python code.
  • The generated code is now correct C89 again, removing some C++ style // comments and C99-style declaration-after-code code ordering. This is still relevant for some ols C compilers, specifically ones that match old Python 2.7 installations.

3.0.7 (2023-12-19)

Bugs fixed

  • In the iterator of generator expressions, await and yield were not correctly analysed. (Github issue 5851)
  • cpdef enums with the same name cimported from different modules could lead to invalid C code. (Github issue 5887)
  • Some declarations in cpython.unicode were fixed and extended. (Github issue 5902)
  • Compiling fused types used in pxd files could crash Cython in Python 3.11+. (Github issues 5894, 5588)
  • Source files with non-ASCII file names could crash Cython. (Github issue 5873)
  • Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.37 release.

3.0.6 (2023-11-26)

Features added

  • Fused def function dispatch is a bit faster.
  • Declarations for the wchar PyUnicode API were added. (Github issue 5836)
  • The Python "nogil" fork is now also detected with the new Py_GIL_DISABLED macro. Patch by Hugo van Kemenade. (Github issue 5852)

Bugs fixed

  • Comparing dataclasses could give different results than Python. (Github issue 5857)
  • float(std::string) generated invalid C code. (Github issue 5818)
  • Using cpdef functions with cimport_from_pyx failed. (Github issue 5795)
  • A crash was fixed when string-formatting a Python value fails. (Github issue 5787)
  • On item access, Cython could try the sequence protocol before the mapping protocol in some cases if an object supports both. (Github issue 5776)
  • A C compiler warning was resolved. (Github issue 5794)
  • Complex numbers failed to compile in MSVC with C11. Patch by Lysandros Nikolaou. (Github issue 5809)
  • Some issues with the Limited API and with PyPy were resolved. (Github issues 5695, 5696)
  • A C++ issue in Python 3.13 was resolved. (Github issue 5790)
  • Several directives are now also available (as no-ops) in Python code. (Github issue 5803)
  • An error message was corrected. Patch by Mads Ynddal. (Github issue 5805)

3.0.5 (2023-10-31)

Features added

  • Preliminary support for CPython 3.13a1 was added to allow early testing. (Github issue 5767)

Bugs fixed

  • A compiler crash was fixed. (Github issue 5771)
  • A typo in the always_allow_keywords directive for Python code was fixed. Patch by lk-1984. (Github issue 5772)
  • Some C compiler warnings were resolved. Patch by Pierre Jolivet. (Github issue 5780)

3.0.4 (2023-10-17)

Features added

  • A new compiler directive show_performance_hints was added to disable the newly added performance hint output. (Github issue 5748)

Bugs fixed

  • `cythonize` requireddistutils` even for operations that did not build binaries. (Github issue :issue:`5751)
  • A regression in 3.0.3 was fixed that prevented calling inline functions from another inline function in .pxd files. (Github issue 5748)
  • Some C compiler warnings were resolved. Patch by Pierre Jolivet. (Github issue 5756)

3.0.3 (2023-10-05)

Features added

  • More warnings were added to help users migrate and avoid bugs. (Github issue 5650)
  • A warning-like category for performance hints was added that bypasses -Werror. (Github issue 5673)
  • FastGIL now uses standard thread_local in C++. (Github issue 5640)
  • reference_wrapper was added to libcpp.functional. Patch by Vyas Ramasubramani. (Github issue 5671)
  • The cythonize command now supports the --cplus option known from the cython command. (Github issue 5736)

Bugs fixed

  • Performance regressions where the GIL was needlessly acquired were fixed. (Github issues 5670, 5700)
  • A reference leak for exceptions in Python 3.12 was resolved. Patch by Eric Johnson. (Github issue 5724)
  • fastcall calls with keyword arguments generated incorrect C code. (Github issue 5665)
  • Assigning the type converted result of a conditional (if-else) expression to int or bool variables could lead to incorrect C code. (Github issue 5731)
  • Early (unlikely) failures in Python function wrappers no longer set a traceback in order to simplify the C code flow. Being mostly memory allocation errors, they probably would never have created a traceback anyway. (Github issue 5681)
  • Relative cimports from packages with __init__.py files could fail. (Github issue 5715)
  • Several issues with the Limited API support were resolved. (Github issues 5641, 5648, 5689)
  • The code generated for special-casing both Cython functions and PyCFunctions was cleaned up to avoid calling C-API functions that were not meant for the other type respectively. This could previously trigger assertions in CPython debug builds and now also plays better with the Limited API. (Github issues 4804, 5739)
  • Fix some C compiler warnings. Patches by Ralf Gommers, Oleksandr Pavlyk, Sebastian Koslowski et al. (Github issues 5651, 5663, 5668, 5717, 5726, 5734)
  • Generating gdb debugging information failed when using generator expressions. Patch by Oleksandr Pavlyk. (Github issue 5552)
  • Passing a setuptools.Extension into cythonize() instead of a distutils.Extension could make it miss the matching extensions.
  • cython -M needlessly required distutils, which made it fail in Python 3.12. (Github issue 5681)

Other changes

  • The visible deprecation warning for DEF was removed again since it proved difficult for some users to migrate away from it. The statement is still meant to be removed at some point (and thus, like IF, should not be used in new code), but the time for sunset is probably not around the corner. (Github issue 4310)
  • The np_pythran option raise a DeprecationWarning if it receives other values than True and False. This will eventually be disallowed (in line with all other boolean options).

3.0.2 (2023-08-27)

Bugs fixed

  • Using None as default value for arguments annotated as int could crash Cython. (Github issue 5643)
  • Default values of fused types that include complex could generate invalid C code with -DCYTHON_CCOMPLEX=0. (Github issue 5644)
  • Using C++ enum class types in extension type method signatures could generate invalid C code. (Github issue 5637)

3.0.1 (2023-08-25)

Features added

  • The error messages regarding exception declarations were improved in order to give better help about possible reasons and fixes. (Github issue 5547)

Bugs fixed

  • Memory view types in Python argument annotations no longer accept None. They now require an explicit Optional[] or a None default value in order to allow None to be passed. This was an oversight in the 3.0.0 release and is a BACKWARDS INCOMPATIBLE change. However, since it only applies to code using Python syntax, it probably only applies to newly written code that was written for Cython 3.0 and can easily be adapted. In most cases, we expect that this change will avoid bugs in user code rather than produce problems. (Github issue 5612)
  • nogil functions using parallel code could freeze when called with the GIL held. (Github issues 5564, 5573)
  • Relative cimports could end up searching globally and find the same package installed elsewhere, potentially in another version. (Github issue 5511)
  • Attribute lookups on known standard library modules could accidentally search in the module namespace instead. (Github issue 5536)
  • Using constructed C++ default arguments could generate invalid C++ code. (Github issue 5553)
  • libcpp.memory.make_unique() was lacking C++ exception handling. (Github issue 5560)
  • Some non-public and deprecated CAPI usages were replaced by public (and thus more future proof) API code.
  • Many issues with the Limited API support were resolved. Patches by Lisandro Dalcin et al. (Github issues 5549, 5550, 5556, 5605, 5617)
  • Some C compiler warnings were resolved. Patches by Matti Picus et al. (Github issues 5557, 5555)
  • Large Python integers are now stored in hex instead of decimal strings to work around security limits in Python and generally speed up their Python object creation.
  • NULL could not be used as default for fused type pointer arguments. (Github issue 5554)
  • C functions that return pointer types now return NULL as default exception value. Previously, calling code wasn't aware of this and always tested for raised exceptions. (Github issue 5554)
  • Untyped literal default arguments in fused functions could generate invalid C code. (Github issue 5614)
  • C variables declared as const could generate invalid C code when used in closures, generator expressions, ctuples, etc. (Github issues 5558, 5333)
  • Enums could not refer to previously defined enums in their definition. (Github issue 5602)
  • The Python conversion code for anonymous C enums conflicted with regular int conversion. (Github issue 5623)
  • Using memory views for property methods (and other special methods) could lead to refcounting problems. (Github issue 5571)
  • Star-imports could generate code that tried to assign to constant C macros like PY_SSIZE_T_MAX and PY_SSIZE_T_MIN. Patch by Philipp Wagner. (Github issue 5562)
  • CYTHON_USE_TYPE_SPECS can now be (explicitly) enabled in PyPy.
  • The template parameter "delimeters" in the Tempita Template class was corrected to "delimiters". The old spelling is still available in the main template API but now issues a DeprecationWarning. (Github issue 5608)
  • The cython --version output is now less likely to reach both stdout and stderr. Patch by Eli Schwartz. (Github issue 5504)
  • The sdist was missing the Shadow.pyi stub file.

3.0.0 unified release notes

Cython 3.0.0 has been a very large effort that cleaned up many old warts, introduced many new features, and introduces a couple of intentional behaviour changes, even though the goal remained to stay compatible as much as possible with Cython 0.29.x. For details, see the migration guide.

As the development was spread out over several years, a lot of things have happened in the meantime. Many crucial bugfixes and some features were backported to 0.29.x and are not strictly speaking "new" in Cython 3.0.0.

Major themes in 3.0.0

Compatibility with CPython and the Python C API

Since Cython 3.0.0 started development, CPython 3.8-3.11 were released. All these are supported in Cython, including experimental support for the in-development CPython 3.12. On the other end of the spectrum, support for Python 2.6 was dropped.

Cython interacts very closely with the C-API of Python, which is where most of the adaptation work happens.

Related changes

  • The long deprecated include files python_*, stdio, stdlib and stl in Cython/Includes/Deprecated/ were removed. Use the libc.* and cpython.* pxd modules instead. Patch by Jeroen Demeyer. (Github issue 2904)
  • The Py_hash_t type failed to accept arbitrary "index" values. (Github issue 2752)
  • @cython.trashcan(True) can be used on an extension type to enable the CPython trashcan. This allows deallocating deeply recursive objects without overflowing the stack. Patch by Jeroen Demeyer. (Github issue 2842)
  • PyEval_InitThreads() is no longer used in Py3.7+ where it is a no-op.
  • A low-level inline function total_seconds(timedelta) was added to cpython.datetime to bypass the Python method call. Note that this function is not guaranteed to give exactly the same results for very large time intervals. Patch by Brock Mendel. (Github issue 3616)
  • The internal CPython macro Py_ISSPACE() is no longer used. Original patch by Andrew Jones. (Github issue 4111)
  • The value PyBUF_MAX_NDIM was added to the cpython.buffer module. Patch by John Kirkham. (Github issue 3811)
  • A new module cpython.time was added with some low-level alternatives to Python's time module. Patch by Brock Mendel. (Github issue 3767)
  • More C-API declarations for cpython.datetime were added. Patch by Bluenix2. (Github issue 4128)
  • C-API declarations for context variables in Python 3.7 were added. Original patch by Zolisa Bleki. (Github issue 2281)
  • C-API declarations for cpython.fileobject were added. Patch by Zackery Spytz. (Github issue 3906)
  • The signature of PyFloat_FromString() in cpython.float was changed to match the signature in Py3. It still has an automatic fallback for Py2. (Github issue 3909)
  • PyMem_[Raw]Calloc() was added to the cpython.mem declarations. Note that the Raw versions are no longer #defined by Cython. The previous macros were not considered safe. Patch by William Schwartz and David Woods. (Github issue 3047)
  • The runtime size check for imported PyVarObject types was improved to reduce false positives and adapt to Python 3.11. Patch by David Woods. (Github issues 4827, 4894)
  • The generated C code failed to compile in CPython 3.11a4 and later. (Github issue 4500)
  • pyximport no longer uses the deprecated imp module. Patch by Matúš Valo. (Github issue 4560)
  • Improvements to PyTypeObject definitions in pxd wrapping of libpython. Patch by John Kirkham. (Github issue 4699)
  • Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue 4640)
  • cpdef enums no longer use OrderedDict but dict in Python 3.6 and later. Patch by GalaxySnail. (Github issue 5180)
  • Several problems with CPython 3.12 were resolved. (Github issue 5238)
  • The exception handling code was adapted to CPython 3.12. (Github issue 5442)
  • The Python int handling code was adapted to make use of the new PyLong internals in CPython 3.12. (Github issue 5353)
  • A compile error when using __debug__ was resolved.
  • The deprecated _PyGC_FINALIZED() C-API macro is no longer used. Patch by Thomas Caswell and Matúš Valo. (Github issue 5481)
  • A crash in Python 2.7 was fixed when cleaning up extension type instances at program end.

Compatibility with other Python implementations

Cython tries to support other Python implementations, largely on a best-effort basis. The most advanced support exists for PyPy, which is tested in our CI and considered supported.

Related changes

  • An unsupported C-API call in PyPy was fixed. Patch by Max Bachmann. (Github issue 4055)
  • Support for the now unsupported Pyston V1 was removed in favour of Pyston V2. Patch by Marius Wachtler. (Github issue 4211)
  • A C compiler warning in PyPy3 regarding PyEval_EvalCode() was resolved.
  • Some compatibility issues with PyPy were resolved. Patches by Max Bachmann, Matti Picus. (Github issues 4454, 4477, 4478, 4509, 4517)
  • An initial set of adaptations for GraalVM Python was implemented. Note that this does not imply any general support for this target or that your code will work at all in this environment. But testing should be possible now. Patch by David Woods. (Github issue 4328)
  • A work-around for StacklessPython < 3.8 was disabled in Py3.8 and later. (Github issue 4329)

Initial support for Limited API

CPython provides a stable, limited subset of its C-API as the so-called Limited API. This C-API comes with the guarantee of a stable ABI, meaning that extensions modules that were compiled for one version of CPython can also be imported in later versions without recompilation.

There is initial support for this in Cython. By defining the CYTHON_LIMITED_API macro, Cython cuts down its C-API usage and tries to adhere to the Limited C-API, probably at the cost of a bit of performance. In order to get full benefit from the limited API you will also need to define the CPython macro Py_LIMITED_API to a specific CPython compatibility version, which additionally restricts the C-API during the C compilation, thus enforcing the forward compatibility of the extension module.

Note that "initial support" in Cython really means that setting the Py_LIMITED_API macro will almost certainly not yet work for your specific code. There are limitations in the Limited C-API that are difficult for Cython to generate C code for, so some advanced Python features (like async code) may not lead to C code that cannot adhere to the Limited C-API, or where Cython simply does not know yet how to adhere to it. Basically, if you get your code to compile with both macros set, and it passes your test suite, then it should be possible to import the extension module also in later CPython versions.

The experimental feature flags CYTHON_USE_MODULE_STATE and CYTHON_USE_TYPE_SPECS enable some individual aspects of the Limited API implementation independently.

Related changes

  • Preliminary support for the CPython's Py_LIMITED_API (stable ABI) is available by setting the CYTHON_LIMITED_API C macro. Note that the support is currently in an early stage and many features do not yet work. You currently still have to define Py_LIMITED_API externally in order to restrict the API usage. This will change when the feature stabilises. Patches by Eddie Elizondo and David Woods. (Github issues 3223, 3311, 3501)
  • Limited API support was improved. Patches by Matthias Braun. (Github issues 3693, 3707)
  • New C feature flags: CYTHON_USE_MODULE_STATE, CYTHON_USE_TYPE_SPECS Both are currently considered experimental. (Github issue 3611)
  • _Py_TPFLAGS_HAVE_VECTORCALL was always set on extension types when using the limited API. Patch by David Woods. (Github issue 4453)
  • Limited API C preprocessor warning is compatible with MSVC. Patch by Victor Molina Garcia. (Github issue 4826)
  • The embedding code no longer calls deprecated C-API functions but uses the new PyConfig API instead on CPython versions that support it (3.8+). Patch by Alexander Shadchin. (Github issue 4895)
  • Some C code issue were resolved for the Limited API target. (Github issues 5264, 5265, 5266)
  • Conversion of Python ints to C int128 is now always supported, although slow if dedicated C-API support is missing (_PyLong_AsByteArray()), specifically in the Limited C-API. (Github issue 5419)
  • Custom buffer slot methods are now supported in the Limited C-API of Python 3.9+. Patch by Lisandro Dalcin. (Github issue 5422)

Improved fidelity to Python semantics

Implemented PEPs

  • PEP-3131: Supporting Non-ASCII Identifiers (Github issue 2601)
  • PEP-479: generator_stop (enabled by default for language_level=3) (Github issue 2580)
  • PEP-487: Simpler customisation of class creation (Github issue 2781)
  • PEP-563: Postponed Evaluation of Annotations (Github issue 3285)
  • PEP-570: Positional-Only Parameters (Github issue 2915)
  • PEP-572: Assignment Expressions (a.k.a. the walrus operator :=) (Github issue 2636)
  • PEP-590: Vectorcall protocol (Github issue 2263)
  • PEP-614: Relaxing Grammar Restrictions On Decorators (Github issue 4570)

Typing support in the sense of PEP-484 (Github issues 3949, 4243) and PEP-560 (Github issues 2753, 3537, 3764) was also improved.

The default language level was changed to 3str, i.e. Python 3 semantics, but with str literals (also in Python 2.7). This is a backwards incompatible change from the previous default of Python 2 semantics. The previous behaviour is available through the directive language_level=2. (Github issue 2565). This covers changes such as using the print-function instead of the print-statement, and integer-integer division giving a floating point answer. Most of these changes were available in earlier versions of Cython but are now the default.

Cython 3.0.0 also aligns its own language semantics more closely with Python, in particular:

  • the power operator has changed to give a result matching what Python does rather than keeping the same types as the input (as in C),
  • operator overloading of cdef classes behaves much more like Python classes,
  • Cython's behaviour when using type annotations aligns more closely with their standard use in Python.

Related changes

  • Cython no longer generates __qualname__ attributes for classes in Python 2.x since they are problematic there and not correctly maintained for subclasses. Patch by Jeroen Demeyer. (Github issue 2772)
  • Binding staticmethods of Cython functions were not behaving like Python methods. Patch by Jeroen Demeyer. (Github issue 3106, 3102)
  • Compiling package __init__ files could fail under Windows due to an undefined export symbol. (Github issue 2968)
  • __init__.pyx files were not always considered as package indicators. (Github issue 2665)
  • Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue 2791)
  • __doc__ was not available inside of the class body during class creation. (Github issue 1635)
  • The first function line number of functions with decorators pointed to the signature line and not the first decorator line, as in Python. Patch by Felix Kohlgrüber. (Github issue 2536)
  • Pickling unbound methods of Python classes failed. Patch by Pierre Glaser. (Github issue 2972)
  • Item access (subscripting) with integer indices/keys always tried the Sequence protocol before the Mapping protocol, which diverged from Python semantics. It now passes through the Mapping protocol first when supported. (Github issue 1807)
  • Nested dict literals in function call kwargs could incorrectly raise an error about duplicate keyword arguments, which are allowed when passing them from dict literals. (Github issue 2963)
  • Diverging from the usual behaviour, len(memoryview), len(char*) and len(Py_UNICODE*) returned an unsigned size_t value. They now return a signed Py_ssize_t, like other usages of len().
  • The unicode methods .upper(), .lower() and .title() were incorrectly optimised for single character input values and only returned the first character if multiple characters should have been returned. They now use the original Python methods again.
  • The cython.view.array type supports inheritance. Patch by David Woods. (Github issue 3413)
  • The builtin abs() function can now be used on C numbers in nogil code. Patch by Elliott Sales de Andrade. (Github issue 2748)
  • The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection. (Github issue 2306)
  • Inlined properties can be defined for external extension types. Patch by Matti Picus. (Github issue 2640, redone later in 3571)
  • Unicode module names and imports are supported. Patch by David Woods. (Github issue 3119)
  • __arg argument names in methods were not mangled with the class name. Patch by David Woods. (Github issue 1382)
  • With language_level=3/3str, Python classes without explicit base class are now new-style (type) classes also in Py2. Previously, they were created as old-style (non-type) classes. (Github issue 3530)
  • Conditional blocks in Python code that depend on cython.compiled are eliminated at an earlier stage, which gives more freedom in writing replacement Python code. Patch by David Woods. (Github issue 3507)
  • Python private name mangling now falls back to unmangled names for non-Python globals, since double-underscore names are not uncommon in C. Unmangled Python names are also still found as a legacy fallback but produce a warning. Patch by David Woods. (Github issue 3548)
  • The print statement (not the print() function) is allowed in nogil code without an explicit with gil section.
  • repr() was assumed to return str instead of unicode with language_level=3. (Github issue 3736)
  • Type inference now understands that a, *b = x assigns a list to b.
  • No/single argument functions now accept keyword arguments by default in order to comply with Python semantics. The marginally faster calling conventions METH_NOARGS and METH_O that reject keyword arguments are still available with the directive @cython.always_allow_keywords(False). (Github issue 3090)
  • Special methods for binary operators now follow Python semantics. Rather than e.g. a single __add__ method for cdef classes, where "self" can be either the first or second argument, one can now define both __add__ and __radd__ as for standard Python classes. This behavior can be disabled with the c_api_binop_methods directive to return to the previous semantics in Cython code (available from Cython 0.29.20), or the reversed method (__radd__) can be implemented in addition to an existing two-sided operator method (__add__) to get a backwards compatible implementation. (Github issue 2056)
  • Generator expressions in pxd-overridden cdef functions could fail to compile. Patch by Matúš Valo. (Github issue 3477)
  • Calls to .__class__() of a known extension type failed. Patch by David Woods. (Github issue 3954)
  • Structs could not be instantiated with positional arguments in pure Python mode.
  • Annotations were not exposed on annotated (data-)classes. Patch by matsjoyce. (Github issue 4151)
  • Docstrings of cpdef enums are now copied to the enum class. Patch by matham. (Github issue 3805)
  • asyncio.iscoroutinefunction() now recognises coroutine functions also when compiled by Cython. Patch by Pedro Marques da Luz. (Github issue 2273)
  • Self-documenting f-strings (=) were implemented. Patch by davfsa. (Github issue 3796)
  • cython.array supports simple, non-strided views. (Github issue 3775)
  • Attribute annotations in Python classes are now ignored, because they are just Python objects in a dict (as opposed to the fields of extension types). Patch by David Woods. (Github issues 4196, 4198)
  • A warning was added when __defaults__ or __kwdefaults__ of Cython compiled functions were re-assigned, since this does not current have an effect. Patch by David Woods. (Github issue 2650)
  • The self argument of static methods in .pxd files was incorrectly typed. Patch by David Woods. (Github issue 3174)
  • Default values for memory views arguments were not properly supported. Patch by Corentin Cadiou. (Github issue 4313)
  • Python object types were not allowed as -> return type annotations. Patch by Matúš Valo. (Github issue 4433)
  • The excess arguments in a for-in-range loop with more than 3 arguments to range() were silently ignored. Original patch by Max Bachmann. (Github issue 4550)
  • Unsupported decorators on cdef functions were not rejected in recent releases. Patch by David Woods. (Github issue 4322)
  • Fused functions were binding unnecessarily, which prevented them from being pickled. Patch by David Woods. (Github issue 4370)
  • Decorators on inner functions were not evaluated in the right scope. Patch by David Woods. (Github issue 4367)
  • Cython did not type the self argument in special binary methods. Patch by David Woods. (Github issue 4434)
  • Circular imports of compiled modules could fail needlessly even when the import could already be resolved from sys.modules. Patch by Syam Gadde. (Github issue 4390)
  • __del__(self) on extension types now maps to tp_finalize in Python 3. Original patch by ax487. (Github issue 3612)
  • Reusing an extension type attribute name as a method name is now an error. Patch by 0dminnimda. (Github issue 4661)
  • When using type annotations, func(x: list) or func(x: ExtType) (and other Python builtin or extension types) no longer allow None as input argument to x. This is consistent with the normal typing semantics in Python, and was a common gotcha for users who did not expect None to be allowed as input. To allow None, use typing.Optional as in func(x: Optional[list]). None is also automatically allowed when it is used as default argument, i.e. func(x: list = None). int and float are now also recognised in type annotations and restrict the value type at runtime. They were previously ignored. Note that, for backwards compatibility reasons, the new behaviour does not apply when using Cython's C notation, as in func(list x). Here, None is still allowed, as always. Also, the annotation_typing directive can now be enabled and disabled more finely within the module. (Github issues 2696, 3883, 4606, 4669, 4886)
  • The parser allowed some invalid spellings of .... Patch by 0dminnimda. (Github issue 4868)
  • The __self__ attribute of fused functions reports its availability correctly with hasattr(). Patch by David Woods. (Github issue 4808)
  • Several optimised string methods failed to accept None as arguments to their options. Test patch by Kirill Smelkov. (Github issue 4737)
  • Cython generators and coroutines now identify as CO_ASYNC_GENERATOR, CO_COROUTINE and CO_GENERATOR accordingly. (Github issue 4902)
  • Memory views and the internal Cython array type now identify as collections.abc.Sequence. Patch by David Woods. (Github issue 4817)
  • Context managers can be written in parentheses. Patch by David Woods. (Github issue 4814)
  • Some parser issues were resolved. (Github issue 4992)
  • Unused **kwargs arguments did not show up in locals(). (Github issue 4899)
  • Relative imports failed in compiled __init__.py package modules. Patch by Matúš Valo. (Github issue 3442)
  • Extension types are now explicitly marked as immutable types to prevent them from being considered mutable. Patch by Max Bachmann. (Github issue 5023)
  • int(Py_UCS4) returned the code point instead of the parsed digit value. (Github issue 5216)
  • Calling bound classmethods of builtin types could fail trying to call the unbound method. (Github issue 5051)
  • Generator expressions and comprehensions now look up their outer-most iterable on creation, as Python does, and not later on start, as they did previously. (Github issue 1159)
  • Bound C methods can now coerce to Python objects. (Github issues 4890, 5062)
  • cpdef enums can now be pickled. (Github issue 5120)
  • The Python Enum of a cpdef enum now inherits from IntFlag to better match both Python and C semantics of enums. (Github issue 2732)
  • The special __*pow__ methods now support the 2- and 3-argument variants. (Github issue 5160)
  • The ** power operator now behaves more like in Python by returning the correct complex result if required by math. A new cpow directive was added to turn on the previous C-like behaviour. (Github issue 4936)
  • With language_level=2, imports of modules in packages could return the wrong module in Python 3. (Github issue 5308)
  • Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue 5355)
  • __qualname__ and __module__ were not available inside of class bodies. (Github issue 4447)
  • A new directive embedsignature.format was added to select the format of the docstring embedded signatures between python, c and argument clinic. Patch by Lisandro Dalcin. (Github issue 5415)
  • ctuples can now be assigned from arbitrary sequences, not just Python tuples.

Improvements in Pure Python mode

Cython strives to be able to parse newer Python constructs for use with its pure python mode, which has been a focus. In short, this allows to compile a wider range of Python code into optimized C code.

Pure python mode gained many new features and was generally overhauled to make it as capable as the Cython syntax. Except for using external C/C++ libraries, it should now be possible to express all Cython code and use all features in regular Python syntax. The very few remaining exceptions or bugs are noted in the documentation.

Additionally, the documentation has been substantially updated (primarily by Matúš Valo and 0dminnimda) to show both the older Cython syntax and pure Python syntax.

Related changes

  • The cython.declare() and cython.cast() functions could fail in pure mode. Patch by Dmitry Shesterkin. (Github issue 3244)
  • Fused argument types were not correctly handled in type annotations and cython.locals(). Patch by David Woods. (Github issues 3391, 3142)
  • nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue 3554)
  • The @returns() decorator propagates exceptions by default for suitable C return types when no @exceptval() is defined. (Github issues 3625, 3664)
  • Extension types inheriting from Python classes could not safely be exposed in .pxd files. (Github issue 4106)
  • Default arguments of methods were not exposed for introspection. Patch by Vladimir Matveev. (Github issue 4061)
  • Literal list assignments to pointer variables declared in PEP-526 notation failed to compile.
  • The type cython.Py_hash_t is available in Python mode.
  • A cimport is now supported in pure Python code by prefixing the imported module name with cython.cimports., e.g. from cython.cimports.libc.math import sin. (GIthub issue 4190)
  • Directives starting with optimization.* in pure Python mode were incorrectly named. It should have been optimize.*. Patch by David Woods. (Github issue 4258)
  • Invalid and misspelled cython.* module names were not reported as errors. (Github issue 4947)
  • The annotation_typing directive was missing in pure Python mode. Patch by 0dminnimda. (Github issue 5194)
  • Memoryviews with object item type were not supported in Python type declarations. (Github issue 4907)
  • Subscripted builtin types in type declarations (like list[float]) are now better supported. (Github issue 5058)
  • Unknown type annotations (e.g. because of typos) now emit a warning at compile time. Patch by Matúš Valo. (Github issue 5070)
  • typing.Optional could fail on tuple types. (Github issue 5263)
  • from cython cimport … as … could lead to imported names not being found in annotations. Patch by Chia-Hsiang Cheng. (Github issue 5235)
  • Simple tuple types like (int, int) are no longer accepted in Python annotations and require the Python notation instead (e.g. tuple[cython.int, cython.int]). (Github issue 5397)
  • The Python implementation of cimport cython.cimports… could raise an ImportError instead of an AttributeError when looking up package variable names. Patch by Matti Picus. (Github issue 5411)
  • A new decorator @cython.with_gil is available in Python code to match the with gil function declaration in Cython syntax.
  • with gil and with nogil(flag) now accept their flag argument also in Python code. Patch by Matúš Valo. (Github issue 5113)

Code generation changes

Cython has gained several major new features that speed up both the development and the code. Dataclasses have gained an extension type equivalent that implements the dataclass features in C code. Similarly, the @functools.total_ordering decorator to an extension type will implement the comparison functions in C.

Finally, NumPy ufuncs can be generated from simple computation functions with the new @cython.ufunc decorator.

Related changes

  • with gil/nogil statements can be conditional based on compile-time constants, e.g. fused type checks. Patch by Noam Hershtig. (Github issue 2579)
  • The names of Cython's internal types (functions, generator, coroutine, etc.) are now qualified with the module name of the internal Cython module that is used for sharing them across Cython implemented modules, for example _cython_3_0a5.coroutine. This was done to avoid making them look like homeless builtins, to help with debugging, and in order to avoid a CPython warning according to https://bugs.python.org/issue20204
  • A @cython.total_ordering decorator has been added to automatically implement all comparison operators, similar to functools.total_ordering. Patch by Spencer Brown. (Github issue 2090)
  • A new decorator @cython.dataclasses.dataclass was implemented that provides compile time dataclass generation capabilities to cdef classes (extension types). Patch by David Woods. (Github issue 2903). kw_only dataclasses added by Yury Sokov. (Github issue 4794)
  • A new function decorator @cython.ufunc automatically generates a (NumPy) ufunc that applies the calculation function to an entire memoryview. (Github issue 4758)
  • Generated NumPy ufuncs could crash for large arrays due to incorrect GIL handling. (Github issue 5328)
  • Some invalid directive usages are now detected and rejected, e.g. using @ccall together with @cfunc, and applying @cfunc to a @ufunc. Cython also warns now when a directive is applied needlessly. (Github issue 5399 et al.)
  • The normal @dataclasses.dataclass and @functools.total_ordering decorators can now be used on extension types. Using the corresponding @cython.* decorator will automatically turn a Python class into an extension type (no need for @cclass). (Github issue 5292)

Interaction with numpy

The NumPy declarations (cimport numpy) were moved over to the NumPy project in order to allow version specific changes on their side.

One effect is that Cython does not use deprecated NumPy C-APIs any more. Thus, you can define the respective NumPy C macro to get rid of the compatibility warning at C compile time.

Related changes

  • cython.inline() now sets the NPY_NO_DEPRECATED_API=NPY_1_7_API_VERSION C macro automatically when numpy is imported in the code, to avoid C compiler warnings about deprecated NumPy C-API usage.
  • Deprecated NumPy API usages were removed from numpy.pxd. Patch by Matti Picus. (Github issue 3365)
  • numpy.import_array() is automatically called if numpy has been cimported and it has not been called in the module code. This is intended as a hidden fail-safe so user code should continue to call numpy.import_array. Patch by David Woods. (Github issue 3524)
  • The outdated getbuffer/releasebuffer implementations in the NumPy declarations were removed so that buffers declared as ndarray now use the normal implementation in NumPy.
  • Several macros/functions declared in the NumPy API are now usable without holding the GIL.
  • The numpy declarations were updated. Patch by Brock Mendel. (Github issue 3630)
  • ndarray.shape failed to compile with Pythran and recent NumPy. Patch by Serge Guelton. (Github issue 3762)
  • A C-level compatibility issue with recent NumPy versions was resolved. Patch by David Woods. (Github issue 4396)
  • The generated modules no longer import NumPy internally when using fused types but no memoryviews. Patch by David Woods. (Github issue 4935)
  • np.long_t and np.ulong_t were removed from the NumPy declarations, syncing Cython with upstream NumPy v1.25.0. The aliases were confusing since they could mean different things on different platforms.

Exception handling

Cython-implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue 4280)

To ease the transition for this break in behaviour, it is possible to set legacy_implicit_noexcept=True.

Related changes

  • The assert statement is allowed in nogil sections. Here, the GIL is only acquired if the AssertionError is really raised, which means that the evaluation of the asserted condition only allows C expressions.
  • The exception handling annotation except +* was broken. Patch by David Woods. (Github issues 3065, 3066)
  • Improve conversion between function pointers with non-identical but compatible exception specifications. Patches by David Woods. (Github issues 4770, 4689)
  • Exceptions within for-loops that run over memoryviews could lead to a ref-counting error. Patch by David Woods. (Github issue 4662)
  • To opt out of the new, safer exception handling behaviour, legacy code can set the new directive legacy_implicit_noexcept=True for a transition period to keep the previous, unsafe behaviour. This directive will eventually be removed in a later release. Patch by Matúš Valo. (Github issue 5094)
  • Cython implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue 4280)
  • The code except +nogil (declaring a C++ exception handler function called nogil) is now rejected because it is almost certainly a typo from except + nogil. (Github issue 5430)
  • Handling freshly raised exceptions that didn't have a traceback yet could crash. (Github issue 5495)

Optimizations

Generating efficient code has long been a goal of Cython, and 3.0 continues that. Probably the most significant change is that Cython functions use the PEP-590 vectorcall protocol on Python 3.7 and higher.

Related changes

  • Name lookups in class bodies no longer go through an attribute lookup. Patch by Jeroen Demeyer. (Github issue 3100)
  • Extension types that do not need their own tp_new implementation (because they have no object attributes etc.) directly inherit the implementation of their parent type if possible. (Github issue 1555)
  • Some list copying is avoided internally when a new list needs to be created but we already have a fresh one. (Github issue 3494)
  • Multiplication of Python numbers with small constant integers is faster. (Github issue 2808)
  • String concatenation can now happen in place if possible, by extending the existing string rather than always creating a new one. Patch by David Woods. (Github issue 3453)
  • The str() builtin now calls PyObject_Str() instead of going through a Python call. Patch by William Ayd. (Github issue 3279)
  • Reimports of already imported modules are substantially faster. (Github issue 2854)
  • The dispatch to fused functions is now linear in the number of arguments, which makes it much faster, often 2x or more, and several times faster for larger fused types with many specialisations. Patch by will-ca. (Github issue 1385)
  • The fastcall/vectorcall protocols are used for several internal Python calls. (Github issue 3540)
  • nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue 3554)
  • Type inference now works for memory views and slices. Patch by David Woods. (Github issue 2227)
  • For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue 2227)
  • For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue 2227)
  • float(…) is optimised for string arguments (str/bytes/bytearray).
  • [...] * N is optimised for C integer multipliers N. (Github issue 3922)
  • Some constant tuples containing strings were not deduplicated. Patch by David Woods. (Github issue 4353)
  • Memory views can use atomic CPU instructions instead of locks in more cases. Patch by Sam Gross. (Github issue 4912)
  • Cython avoids raising StopIteration in __next__ methods when possible. Patch by David Woods. (Github issue 3447)
  • Larger numbers of extension types with multiple subclasses could take very long to compile. Patch by Scott Wolchok. (Github issue 5139)
  • Integer comparisons avoid Python coercions if possible. (Github issue 4821)
  • The call-time dispatch for fused memoryview types is less slow. (Github issue 5073)
  • Python's memoryview is now a known builtin type with optimised properties. (Github issue 3798)
  • Multiplying a sequence by a C integer avoids creating and intermediate Python integer.
  • The reference counting of memory views involved useless overhead. (Github issue 5510)

Compatibility with C

The support for C features like const or volatile was substantially improved.

The generated code has been cleared up to reduce the number of C compiler warnings emitted.

Related changes

  • A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue 2775)
  • Constant integer expressions that used a negative exponent were evaluated as integer 0 instead of the expected float value. Patch by Kryštof Pilnáček. (Github issue 2133)
  • Several declarations in cpython.*, libc.* and libcpp.* were added. Patches by Jeroen Demeyer, Matthew Edwards, Chris Gyurgyik, Jerome Kieffer and Zackery Spytz. (Github issues 3468, 3332, 3202, 3188, 3179, 2891, 2826, 2713)
  • The volatile C modifier is supported in Cython code. Patch by Jeroen Demeyer. (Github issue 1667)
  • const can be used together with fused types. Patch by Thomas Vincent. (Github issue 1772)
  • Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues 3430, 3522)
  • The C property feature has been rewritten and now requires C property methods to be declared inline (3571).
  • Cython generates C compiler branch hints for unlikely user defined if-clauses in more cases, when they end up raising exceptions unconditionally. This now includes exceptions being raised in nogil/with gil sections.
  • Several issues with arithmetic overflow handling were resolved, including undefined behaviour in C. Patch by Sam Sneddon. (Github issue 3588)
  • libc.math was extended to include all C99 function declarations. Patch by Dean Scarff. (Github issue 3570)
  • Some C compiler warninge were resolved. Patches by Max Bachmann. (Github issue 4053, 4059, 4054, 4148, 4162)
  • A C compiler warning about enum value casting was resolved in GCC. (Github issue 2749)
  • A C compiler warning about unused code was resolved. (Github issue 3763)
  • Some compiler problems and warnings were resolved. Patches by David Woods, 0dminnimda, Nicolas Pauss and others. (Github issues 4317, 4324, 4361, 4357)
  • Some C compiler warnings were fixed. Patch by mwtian. (Github issue 4831)
  • A case of undefined C behaviour was resolved in the list slicing code. Patch by Richard Barnes. (Github issue 4734)
  • Typedefs for the bint type did not always behave like bint. Patch by Nathan Manville and 0dminnimda. (Github issue 4660)
  • Intel C compilers could complain about unsupported gcc pragmas. Patch by Ralf Gommers. (Github issue 5052)
  • Structs that contained an array field resulted in incorrect C code. Their initialisation now uses memcpy(). Patch by Chia-Hsiang Cheng. (Github issue 5178)
  • The module state struct was not initialised in correct C (before C23), leading to compile errors on Windows. Patch by yudonglin. (Github issue 5169)
  • cdef public functions declared in .pxd files could use an incorrectly mangled C name. Patch by EpigeneMax. (Github issue 2940)
  • const types could not be returned from functions. Patch by Mike Graham. (Github issue 5135)
  • C11 complex.h is now properly detected. (Github issue 2513)
  • Standard C/C++ atomic operations are now used for memory views, if available. (Github issue 4925)
  • C arrays can be initialised inside of nogil functions. Patch by Matúš Valo. (Github issue 1662)
  • Very long Python integer constants could exceed the maximum C name length of MSVC. Patch by 0dminnimda. (Github issue 5290)
  • Some C compiler warnings were resolved. Patches by Matt Tyson, Lisandro Dalcin, Philipp Wagner, Matti Picus et al. (Github issues 5417, 5418, 5421, 5437, 5438, 5443)
  • Some typedef declarations for libc function types were fixed. (Github issue 5498)
  • With MSVC, Cython no longer enables C-Complex support by accident (which is not supported there). (Github issue 5512)

Compatibility with C++

Many C++ features like forwarding references or std::move are now supported or even used internally, if possible.

Cython's wrapping of the C++ standard library has been extended.

A new cpp_locals` directive enables C++ local variables to initialized when assigned to rather than at the start of the function, making them behave more like Python variables, and also removing the requirement for them to be default constructible.

Related changes

  • C++ typeid() failed for fused types. Patch by David Woods. (Github issue 3203)
  • std::move() is now used in C++ mode for internal temp variables to make them work without copying values. Patch by David Woods. (Github issues 3253, 1612)
  • The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue 3637)
  • C++ references failed to compile when used as Python object indexes. Patch by David Woods. (Github issue 3754)
  • The construct for x in cpp_function_call() failed to compile. Patch by David Woods. (Github issue 3663)
  • Some C++ STL methods did not propagate exceptions. Patch by Max Bachmann. (Github issue 4079)
  • A compile failure for C++ enums in Py3.4 / MSVC was resolved. Patch by Ashwin Srinath. (Github issue 3782)
  • Cython compiled functions always provided a __self__ attribute, regardless of being used as a method or not. Patch by David Woods. (Github issue 4036)
  • Overloaded C++ static methods were lost. Patch by Ashwin Srinath. (Github 1851)
  • Nested C++ types were not usable through ctypedefs. Patch by Vadim Pushtaev. (Github issue 4039)
  • More declarations for C++ string methods were added.
  • Converting C++ containers to Python lists uses less memory allocations. Patch by Max Bachmann. (Github issue 4081)
  • std::move() is now also called for temps during yield. Patch by Yu Feng. (Github issue 4154)
  • The destructor is now called for fields in C++ structs. Patch by David Woods. (Github issue 3226)
  • Conversion from Python dicts to std::map was broken. Patch by David Woods and Mikkel Skofelt. (Github issues 4228, 4231)
  • Code optimisations were not applied to methods of Cython implemented C++ classes. Patch by David Woods. (Github issue 4212)
  • C++17 execution policies are supported in libcpp.algorithm. Patch by Ashwin Srinath. (Github issue 3790)
  • A new directive cpp_locals was added that allows local C++ variables to be lazily initialised (without default constructor), thus making them behave more like Python variables. Patch by David Woods. (Github issue 4160)
  • Generated utility code for C++ conversions no longer depends on several user definable directives that may make it behave incorrectly. Patch by David Woods. (Github issue 4206)
  • Several issues with the new cpp_locals directive were resolved and its test coverage improved. Patch by David Woods. (Github issues 4265, 4266)
  • Declarations for libcpp.algorithms, libcpp.set and libcpp.unordered_set were extended. Patch by David Woods. (Github issues 4271, 4273)
  • Several C++ library declarations were added and fixed. Patches by Dobatymo, account-login, Jonathan Helgert, Evgeny Yakimov, GalaxySnail, Max Bachmann. (Github issues 4408, 4419, 4410, 4395, 4423, 4448, 4462, 3293, 4522, 2171, 4531)
  • Templating C++ classes with memory view types lead to buggy code and is now rejected. Patch by David Woods. (Github issue 3085)
  • prange loops generated incorrect code when cpp_locals is enabled. Patch by David Woods. (Github issue 4354)
  • Direct assignments to C++ references are now allowed. Patch by David Woods. (Github issue 1863)
  • Conversion from Python dict to C++ map now supports arbitrary Python mappings, not just dicts.
  • Some C++ and CPython library declarations were extended and fixed. Patches by Max Bachmann, Till Hoffmann, Julien Jerphanion, Wenjun Si. (Github issues 4530, 4528, 4710, 4746, 4751, 4818, 4762, 4910)
  • Some C/C++ warnings were resolved. Patches by Max Bachmann, Alexander Shadchin, at al. (Github issues 5004, 5005, 5019, 5029, 5096)
  • C++ references did not work on fused types. (Github issue 4717)
  • C++ iteration more safely stores the iterable in temporary variables. Patch by Xavier. (Github issue 3828)
  • C++ post-increment/-decrement operators were not correctly looked up on declared C++ classes, thus allowing Cython declarations to be missing for them and incorrect C++ code to be generated. Patch by Max Bachmann. (Github issue 4536)
  • cdef public functions used an incorrect linkage declaration in C++. Patch by Maximilien Colange. (Github issue 1839)
  • Declarations were added for the C++ bit operations, some other parts of C++20 and CPython APIs. Patches by Jonathan Helgert, Dobatymo, William Ayd and Max Bachmann. (Github issues 4962, 5101, 5157, 5163, 5257)
  • cpp_locals no longer have to be "assignable". (Github issue 4558)
  • Nested cppclass definitions are supported. Patch by samaingw. (Github issue 1218)
  • reversed() can now be used together with C++ iteration. Patch by Chia-Hsiang Cheng. (Github issue 5002)
  • Some C++ warnings regarding const usage in internally generated utility code were resolved. Patch by Max Bachmann. (Github issue 5301)
  • Cython generated C++ code accidentally used C++11 features in some cases. (Github issue 5316)
  • Fully qualified C++ names prefixed by a cimported module name could fail to compile. Patch by Chia-Hsiang Cheng. (Github issue 5229)
  • C++ declarations for <cmath>, <numbers> and std::any were added. Patches by Jonathan Helgert and Maximilien Colange. (Github issues 5262, 5309, 5314)
  • The extern "C" and extern "C++" markers that Cython generates for public functions can now be controlled by setting the C macro CYTHON_EXTERN_C.
  • C++ containers of item type bint could conflict with those of item type int. (Github issue 5516)
  • Reverse iteration in C++ no longer removes the const qualifier from the item type. Patch by Isuru Fernando. (Github issue 5478)

Commandline Interface

A number of new options were added to the cython and cythonize commands.

Related changes

  • The command line parser was rewritten and modernised using argparse. Patch by Egor Dranischnikow. (Github issue 2952, 3001)
  • cygdb gives better error messages when it fails to initialise the Python runtime support in gdb. Patch by Volker Weissmann. (Github issue 3489)
  • --no-docstrings option added to cythonize script. Original patch by mo-han. (Github issue 2889)
  • Code annotation accepts a new debugging argument --annotate-fullc that will include the complete syntax highlighted C file in the HTML output. (Github issue 2855)
  • cygdb has a new option --skip-interpreter that allows using a different Python runtime than the one used to generate the debugging information. Patch by Alessandro Molina. (Github issue 4186)
  • cythonize() and the corresponding CLI command now regenerate the output files also when they already exist but were generated by a different Cython version.
  • The cython and cythonize commands ignored non-existing input files without error. Patch by Matúš Valo. (Github issue 4629)
  • cythonize --help now also prints information about the supported environment variables. Patch by Matúš Valo. (Github issue 1711)
  • Using the --working option could lead to sources not being found. Patch by Lisandro Dalcin. (Github issue 5365)
  • Passing a language level and directives on the command line lost the language level setting. Patch by Matúš Valo. (Github issue 5484)
  • cython --version now prints the version to both stdout and stderr (unless that is a TTY). (Github issue 5504)

Build integration

Cython has made a number of improvements both to how it compiles itself and how it integrates with external build tools. Most notably Cython has been moving to use setuptools instead of the deprecated/removed distutils where possible.

The new --depfile option generates dependency files to help integrate Cython with other build tools.

Related changes

  • Binary Linux wheels now follow the manylinux2010 standard. Patch by Alexey Stepanov. (Github issue 3355)
  • The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Patch by Matti Picus. (Github issue 2905)
  • Source file fingerprinting now uses SHA-1 instead of MD5 since the latter tends to be slower and less widely supported these days. (Github issue 2790)
  • The Cython AST code serialiser class CodeWriter in Cython.CodeWriter supports more syntax nodes.
  • Parallel builds of Cython itself (setup.py build_ext -j N) failed on Windows.
  • When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue 2209)
  • .pxd files can now be versioned <versioning> by adding an extension like ".cython-30.pxd" to prevent older Cython versions (than 3.0 in this case) from picking them up. (Github issue 3577)
  • The Cython CodeWriter can now handle more syntax constructs. Patch by Tao He. (Github issue 3514)
  • The Cython CodeWriter mishandled no-argument return statements. Patch by Tao He. (Github issue 3795)
  • Cython now detects when existing output files were not previously generated by itself and refuses to overwrite them. It is a common mistake to name the module file of a wrapper after the library (source file) that it wraps, which can lead to surprising errors when the file gets overwritten.
  • The Cython.Build.BuildExecutable tool no longer executes the program automatically. Use cythonrun for that.
  • Python modules were not automatically recompiled when only their .pxd file changed. Patch by Golden Rockefeller. (Github issue 1428)
  • An unnecessary slow-down at import time was removed from Cython.Distutils. Original patch by Anthony Sottile. (Github issue 4224)
  • A compiler crash when running Cython thread-parallel from distutils was resolved. (Github issue 4503)
  • An incompatibility with recent coverage.py versions was resolved. Patch by David Woods. (Github issue 4440)
  • pyximport now uses cythonize() internally. Patch by Matúš Valo. (Github issue 2304)
  • Cython.Distutils.build_ext now uses cythonize() internally (previously known as new_build_ext), while still supporting the options that were available in the old implementation (old_build_ext). Patch by Matúš Valo. (Github issue 3541)
  • Improve compatibility between classes pickled in Cython 3.0 and 0.29.x by accepting MD5, SHA-1 and SHA-256 checksums. (Github issue 4680)
  • pyximport failed for long filenames on Windows. Patch by Matti Picus. (Github issue 4630)
  • A new Cython build option --cython-compile-minimal was added to compile only a smaller set of Cython's own modules, which can be used to reduce the package and install size.
  • The environment variable CYTHON_FORCE_REGEN=1 can be used to force cythonize to regenerate the output files regardless of modification times and changes.
  • The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27. Patches by Evgeni Burovski and Eli Schwartz. (Github issue 1214)
  • Wheels now include a compiled parser again, which increases their size a little but gives about a 10% speed-up when running Cython.
  • The wheel building process was migrated to use the cibuildwheel tool. Patch by Thomas Li. (Github issue 4736)
  • setup.cfg was missing from the source distribution. (Github issue 5199)
  • Extended glob paths with /**/ and \**\ for finding source files failed on Windows.
  • Coverage analysis failed in projects with a separate source subdirectory. Patch by Sviatoslav Sydorenko and Ruben Vorderman. (Github issue 3636)
  • Cython could crash when finding import files with dots in their names. Patch by Matúš Valo. (Github issue 5396)
  • A module loading problem with cython.inline() on Windows was resolved.

Deprecations

Some older features of Cython have been deprecated. Most notable are the compile time DEF and IF statements, although we emphasise that they will remain until a good alternative exists for all their use-cases.

Related changes

  • Dotted filenames for qualified module names (pkg.mod.pyx) are deprecated. Use the normal Python package directory layout instead. (Github issue 2686)
  • "Declaration after use" is now an error for variables. Patch by David Woods. (Github issue 3976)
  • Variables can no longer be declared with cpdef. Patch by David Woods. (Github issue 887)
  • The compile-time DEF and IF statements are deprecated and generate a warning. They should be replaced with normal constants, code generation or C macros. (Github issue 4310)
  • C-style array declarations (cdef int a[4]) are now (silently) deprecated in favour of the Java-style cdef int[4] a form. The latter was always available and the Python type declaration syntax already used it exclusively (a: int[4]). Patch by Matúš Valo. (Github issue 5248)
  • The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was removed. The type modifier is not needed here and a plain cimport of the name will do. (Github issue 4904)

Editor support

Related changes

  • C compiler warnings and errors are now shown in Jupyter notebooks. Patch by Egor Dranischnikow. (Github issue 3751)
  • An endless loop in cython-mode.el was resolved. Patch by Johannes Mueller. (Github issue 3218)
  • The Emacs Cython mode file cython-mode.el is now maintained in a separate repo: https://github.com/cython/emacs-cython-mode
  • The C code shown in the annotated HTML output could lack the last C code line(s).

Other changes

  • Memoryviews failed to compile when the cache_builtins feature was disabled. Patch by David Woods. (Github issue 3406)
  • Broadcast assignments to a multi-dimensional memory view slice could end up in the wrong places when the underlying memory view is known to be contiguous but the slice is not. (Github issue 2941)
  • The Pythran shape attribute is supported. Patch by Serge Guelton. (Github issue 3307)
  • --no-capture added to runtests.py to prevent stdout/stderr capturing during srctree tests. Patch by Matti Picus. (Github issue 2701)
  • Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3534)
  • Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3531)
  • Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue 1407)
  • Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.
  • Error handling early in the module init code could lead to a crash.
  • Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.
  • A reference leak on import failures was resolved. Patch by Max Bachmann. (Github issue 4056)
  • Casting to ctuples is now allowed. Patch by David Woods. (Github issue 3808)
  • Some issues were resolved that could lead to duplicated C names. Patch by David Woods. (Github issue 3716, 3741, 3734)
  • Inline functions and other code in .pxd files could accidentally inherit the compiler directives of the .pyx file that imported them. Patch by David Woods. (Github issue 1071)
  • Parts of the documentation were (and are being) rewritten to show the Cython language syntax next to the equivalent Python syntax. Patches by 0dminnimda and Matúš Valo. (Github issue 4187)
  • A name collision when including multiple generated API header files was resolved. Patch by David Woods. (Github issue 4308)
  • Very early errors during module initialisation could lead to crashes. Patch by David Woods. (Github issue 4377)
  • Type errors when passing memory view arguments could leak buffer references. Patch by David Woods. (Github issue 4296)
  • The GIL can now safely be released inside of nogil functions (which may actually be called with the GIL held at runtime). Patch by David Woods. (Github issue 4137)
  • The return type of a fused function is no longer ignored for function pointers, since it is relevant when passing them e.g. as argument into other fused functions. Patch by David Woods. (Github issue 4644)
  • Using memoryview arguments in closures of inner functions could lead to ref-counting errors. Patch by David Woods. (Github issue 4798)
  • Decorators like @cfunc and @ccall could leak into nested functions and classes. Patch by David Woods. (Github issue 4092)
  • Cython now uses a .dev0 version suffix for unreleased source installations.
  • The Tempita module no longer contains HTML processing capabilities, which were found to be broken in Python 3.8 and later. Patch by Marcel Stimberg. (Github issue 3309)
  • Nesting fused types in other fused types could fail to specialise the inner type. (Github issue 4725)
  • Iterating over memoryviews in generator expressions could leak a buffer reference. (Github issue 4968)
  • The C float type was not inferred on assignments. (Github issue 5234)
  • Type checks for Python's memoryview type generated incorrect C code. (Github issues 5268, 5270)
  • Auto-generated utility code didn't always have all required user defined types available. (Github issue 5269)
  • cimport_from_pyx could miss some declarations. Patch by Chia-Hsiang Cheng. (Github issue 5318)
  • For-loops now release the internal reference to their list/tuple iterable before instead of after the else: clause. This probably has no practical impact. (Github issue 5347)
  • Extension type hierarchies were generated in the wrong order, thus leading to compile issues. Patch by Lisandro Dalcin. (Github issue 5395)
  • The FAQ page was moved from the GitHub Wiki to the regular documentation to make it more visible.

3.0.0 (2023-07-17)

Bugs fixed

  • A crash in Python 2.7 was fixed when cleaning up extension type instances at program end.

3.0.0 rc 2 (2023-07-13)

Bugs fixed

  • Parser crash on hex/oct enum values. (Github issue 5524)
  • cython --version now prints the version to both stdout and stderr (unless that is a TTY). (Github issue 5504)

3.0.0 rc 1 (2023-07-12)

Features added

  • with gil and with nogil(flag) now accept their flag argument also in Python code. Patch by Matúš Valo. (Github issue 5113)
  • A new decorator @cython.with_gil is available in Python code to match the with gil function declaration in Cython syntax.
  • Assigning a list to a ctuple is slightly faster.

Bugs fixed

  • The reference counting of memory views involved useless overhead. (Github issue 5510)
  • Duplicate values in a cpdef enum could lead to invalid switch statements. (Github issue 5400)
  • Handling freshly raised exceptions that didn't have a traceback yet could crash. (Github issue 5495)
  • Reverse iteration in C++ no longer removes the const qualifier from the item type. Patch by Isuru Fernando. (Github issue 5478)
  • C++ containers of item type bint could conflict with those of item type int. (Github issue 5516)
  • With MSVC, Cython no longer enables C-Complex support by accident (which is not supported there). (Github issue 5512)
  • The Python implementation of cimport cython.cimports… could raise an ImportError instead of an AttributeError when looking up package variable names. Patch by Matti Picus. (Github issue 5411)
  • Passing a language level and directives on the command line lost the language level setting. Patch by Matúš Valo. (Github issue 5484)
  • Some typedef declarations for libc function types were fixed. (Github issue 5498)
  • Some C compiler warnings and errors in CPython 3.12 were resolved.
  • The deprecated _PyGC_FINALIZED() C-API macro is no longer used. Patch by Thomas Caswell and Matúš Valo. (Github issue 5481)
  • A compile error when using __debug__ was resolved.
  • A module loading problem with cython.inline() on Windows was resolved.
  • cython --version now prints the version to stdout instead of stderr. (Github issue 5504)
  • Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.36 release.

Other changes

  • The FAQ page was moved from the GitHub Wiki to the regular documentation to make it more visible.
  • np.long_t and np.ulong_t were removed from the NumPy declarations, syncing Cython with upstream NumPy v1.25.0. The aliases were confusing since they could mean different things on different platforms.

3.0.0 beta 3 (2023-05-24)

Features added

  • Custom buffer slot methods are now supported in the Limited C-API of Python 3.9+. Patch by Lisandro Dalcin. (Github issue 5422)
  • The extern "C" and extern "C++" markers that Cython generates for public functions can now be controlled by setting the C macro CYTHON_EXTERN_C.
  • The Python int handling code was adapted to make use of the new PyLong internals in CPython 3.12. (Github issue 5353)
  • Conversion of Python ints to C int128 is now always supported, although slow if dedicated C-API support is missing (_PyLong_AsByteArray()), specifically in the Limited C-API. (Github issue 5419)
  • The exception handling code was adapted to CPython 3.12. (Github issue 5442)
  • The dataclass implementation was adapted to support Python 3.12. (Github issue 5346)
  • The normal @dataclasses.dataclass and @functools.total_ordering decorators can now be used on extension types. Using the corresponding @cython.* decorator will automatically turn a Python class into an extension type (no need for @cclass). (Github issue 5292)
  • Multiplying a sequence by a C integer avoids creating and intermediate Python integer.
  • ctuples can now be assigned from arbitrary sequences, not just Python tuples.
  • A new directive embedsignature.format was added to select the format of the docstring embedded signatures between python, c and argument clinic. Patch by Lisandro Dalcin. (Github issue 5415)
  • Some invalid directive usages are now detected and rejected, e.g. using @ccall together with @cfunc, and applying @cfunc to a @ufunc. Cython also warns now when a directive is applied needlessly. (Github issue 5399 et al.)
  • Unicode identifier names now allow all letters defined in CPython 3.12.

Bugs fixed

  • Some C compile failures in CPython 3.12.0a6/a7 were resolved.
  • Cascaded comparisons between integer constants and Python types could fail to compile. (Github issue 5354)
  • The internal macro __PYX_IS_UNSIGNED was accidentally duplicated in beta 2 which lead to C compile errors. Patch by 0dminnimda. (Github issue 5356)
  • Memoryviews with typedef item types could fail to match the non-typedef item types. Patch by Yue Yang. (Github issue 5373)
  • Fused memory views could raise a TypeError instead of a ValueError on creation. Patch by Matúš Valo. (Github issue 5401)
  • Cython could crash when finding import files with dots in their names. Patch by Matúš Valo. (Github issue 5396)
  • Selecting a context manager in parentheses and then calling it directly failed to parse. (Github issue 5403)
  • __qualname__ and __module__ were not available inside of class bodies. (Github issue 4447)
  • noexcept was not automatically applied to function pointer attributes in extern structs. Patch by Matúš Valo. (Github issue 5359)
  • Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue 5355)
  • Extension type hierarchies were generated in the wrong order, thus leading to compile issues. Patch by Lisandro Dalcin. (Github issue 5395)
  • Using the --working option could lead to sources not being found. Patch by Lisandro Dalcin. (Github issue 5365)
  • Some C compiler warnings were resolved. Patches by Matt Tyson, Lisandro Dalcin, Philipp Wagner, Matti Picus et al. (Github issues 5417, 5418, 5421, 5437, 5438, 5443)
  • Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.35 release.

Other changes

  • For-loops now release the internal reference to their list/tuple iterable before instead of after the else: clause. This probably has no practical impact. (Github issue 5347)
  • Simple tuple types like (int, int) are no longer accepted in Python annotations and require the Python notation instead (e.g. tuple[cython.int, cython.int]). (Github issue 5397)
  • The code except +nogil (declaring a C++ exception handler function called nogil) is now rejected because it is almost certainly a typo from except + nogil. (Github issue 5430)

3.0.0 beta 2 (2023-03-27)

Features added

  • C++ declarations for <cmath>, <numbers> and std::any were added. Patches by Jonathan Helgert and Maximilien Colange. (Github issues 5262, 5309, 5314)

Bugs fixed

  • Unintended internal exception handling lead to a visible performance regression for nogil memoryview code in 3.0.0b1. (Github issue 5324)
  • None default arguments for arguments with fused memoryview types could select a different implementation in 3.0 than in 0.29.x. The selection behaviour is generally considered suboptimal but was at least reverted to the old behaviour for now. (Github issue 5297)
  • The new complex vs. floating point behaviour of the ** power operator accidentally added a dependency on the GIL, which was really only required on failures. (Github issue 5287)
  • from cython cimport … as … could lead to imported names not being found in annotations. Patch by Chia-Hsiang Cheng. (Github issue 5235)
  • Generated NumPy ufuncs could crash for large arrays due to incorrect GIL handling. (Github issue 5328)
  • Very long Python integer constants could exceed the maximum C name length of MSVC. Patch by 0dminnimda. (Github issue 5290)
  • cimport_from_pyx could miss some declarations. Patch by Chia-Hsiang Cheng. (Github issue 5318)
  • Fully qualified C++ names prefixed by a cimported module name could fail to compile. Patch by Chia-Hsiang Cheng. (Github issue 5229)
  • Cython generated C++ code accidentally used C++11 features in some cases. (Github issue 5316)
  • Some C++ warnings regarding const usage in internally generated utility code were resolved. Patch by Max Bachmann. (Github issue 5301)
  • With language_level=2, imports of modules in packages could return the wrong module in Python 3. (Github issue 5308)
  • typing.Optional could fail on tuple types. (Github issue 5263)
  • Auto-generated utility code didn't always have all required user defined types available. (Github issue 5269)
  • Type checks for Python's memoryview type generated incorrect C code. (Github issues 5268, 5270)
  • Some issues with depfile generation were resolved. Patches by Eli Schwartz. (Github issues 5279, 5291)
  • Some C code issue were resolved for the Limited API target. (Github issues 5264, 5265, 5266)
  • The C code shown in the annotated HTML output could lack the last C code line(s).

3.0.0 beta 1 (2023-02-25)

Features added

  • Cython implemented C functions now propagate exceptions by default, rather than swallowing them in non-object returning function if the user forgot to add an except declaration to the signature. This was a long-standing source of bugs, but can require adding the noexcept declaration to existing functions if exception propagation is really undesired. (Github issue 4280)
  • To opt out of the new, safer exception handling behaviour, legacy code can set the new directive legacy_implicit_noexcept=True for a transition period to keep the previous, unsafe behaviour. This directive will eventually be removed in a later release. Patch by Matúš Valo. (Github issue 5094)
  • A new function decorator @cython.ufunc automatically generates a (NumPy) ufunc that applies the calculation function to an entire memoryview. (Github issue 4758)
  • The ** power operator now behaves more like in Python by returning the correct complex result if required by math. A new cpow directive was added to turn on the previous C-like behaviour. (Github issue 4936)
  • The special __*pow__ methods now support the 2- and 3-argument variants. (Github issue 5160)
  • Unknown type annotations (e.g. because of typos) now emit a warning at compile time. Patch by Matúš Valo. (Github issue 5070)
  • Subscripted builtin types in type declarations (like list[float]) are now better supported. (Github issue 5058)
  • Python's memoryview is now a known builtin type with optimised properties. (Github issue 3798)
  • The call-time dispatch for fused memoryview types is less slow. (Github issue 5073)
  • Integer comparisons avoid Python coercions if possible. (Github issue 4821)
  • The Python Enum of a cpdef enum now inherits from IntFlag to better match both Python and C semantics of enums. (Github issue 2732)
  • PEP-614: decorators can now be arbitrary Python expressions. (Github issue 4570)
  • cpdef enums can now be pickled. (Github issue 5120)
  • Bound C methods can now coerce to Python objects. (Github issues 4890, 5062)
  • C arrays can be initialised inside of nogil functions. Patch by Matúš Valo. (Github issue 1662)
  • reversed() can now be used together with C++ iteration. Patch by Chia-Hsiang Cheng. (Github issue 5002)
  • Standard C/C++ atomic operations are now used for memory views, if available. (Github issue 4925)
  • C11 complex.h is now properly detected. (Github issue 2513)
  • Nested cppclass definitions are supported. Patch by samaingw. (Github issue 1218)
  • cpp_locals no longer have to be "assignable". (Github issue 4558)
  • cythonize --help now also prints information about the supported environment variables. Patch by Matúš Valo. (Github issue 1711)
  • Declarations were added for the C++ bit operations, some other parts of C++20 and CPython APIs. Patches by Jonathan Helgert, Dobatymo, William Ayd and Max Bachmann. (Github issues 4962, 5101, 5157, 5163, 5257)

Bugs fixed

  • Generator expressions and comprehensions now look up their outer-most iterable on creation, as Python does, and not later on start, as they did previously. (Github issue 1159)
  • Type annotations for Python int rejected long under Py2 in the alpha-11 release. They are now ignored again (as always before) when language_level=2, and accept both int and long in Py2 (and only int in Py3) otherwise. (Github issue 4944)
  • Calling bound classmethods of builtin types could fail trying to call the unbound method. (Github issue 5051)
  • int(Py_UCS4) returned the code point instead of the parsed digit value. (Github issue 5216)
  • Several problems with CPython 3.12 were resolved. (Github issue 5238)
  • The C float type was not inferred on assignments. (Github issue 5234)
  • Memoryviews with object item type were not supported in Python type declarations. (Github issue 4907)
  • Iterating over memoryviews in generator expressions could leak a buffer reference. (Github issue 4968)
  • Memory views and the internal Cython array type now identify as collections.abc.Sequence by setting the Py_TPFLAGS_SEQUENCE type flag directly. (Github issue 5187)
  • __del__ finaliser methods were not always called if they were only inherited. (Github issue 4995)
  • Extension types are now explicitly marked as immutable types to prevent them from being considered mutable. Patch by Max Bachmann. (Github issue 5023)
  • const types could not be returned from functions. Patch by Mike Graham. (Github issue 5135)
  • cdef public functions declared in .pxd files could use an incorrectly mangled C name. Patch by EpigeneMax. (Github issue 2940)
  • cdef public functions used an incorrect linkage declaration in C++. Patch by Maximilien Colange. (Github issue 1839)
  • C++ post-increment/-decrement operators were not correctly looked up on declared C++ classes, thus allowing Cython declarations to be missing for them and incorrect C++ code to be generated. Patch by Max Bachmann. (Github issue 4536)
  • C++ iteration more safely stores the iterable in temporary variables. Patch by Xavier. (Github issue 3828)
  • C++ references did not work on fused types. (Github issue 4717)
  • The module state struct was not initialised in correct C (before C23), leading to compile errors on Windows. Patch by yudonglin. (Github issue 5169)
  • Structs that contained an array field resulted in incorrect C code. Their initialisation now uses memcpy(). Patch by Chia-Hsiang Cheng. (Github issue 5178)
  • Nesting fused types in other fused types could fail to specialise the inner type. (Github issue 4725)
  • The special methods __matmul__, __truediv__, __floordiv__ failed to type their self argument. (Github issue 5067)
  • Coverage analysis failed in projects with a separate source subdirectory. Patch by Sviatoslav Sydorenko and Ruben Vorderman. (Github issue 3636)
  • The annotation_typing directive was missing in pure Python mode. Patch by 0dminnimda. (Github issue 5194)
  • The @dataclass directive was accidentally inherited by methods and subclasses. (Github issue 4953)
  • Some issues with Cython @dataclass arguments, hashing, inheritance and repr() were resolved. (Github issues 4956, 5046)
  • cpdef enums no longer use OrderedDict but dict in Python 3.6 and later. Patch by GalaxySnail. (Github issue 5180)
  • Larger numbers of extension types with multiple subclasses could take very long to compile. Patch by Scott Wolchok. (Github issue 5139)
  • Relative imports failed in compiled __init__.py package modules. Patch by Matúš Valo. (Github issue 3442)
  • Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue 4640)
  • The cython and cythonize commands ignored non-existing input files without error. Patch by Matúš Valo. (Github issue 4629)
  • Invalid and misspelled cython.* module names were not reported as errors. (Github issue 4947)
  • Unused **kwargs arguments did not show up in locals(). (Github issue 4899)
  • Extended glob paths with /**/ and \**\ for finding source files failed on Windows.
  • Annotated HTML generation was missing newlines in 3.0.0a11. (Github issue 4945)
  • Some parser issues were resolved. (Github issue 4992)
  • setup.cfg was missing from the source distribution. (Github issue 5199)
  • Some C/C++ warnings were resolved. Patches by Max Bachmann, Alexander Shadchin, at al. (Github issues 5004, 5005, 5019, 5029, 5096)
  • The embedding code no longer calls deprecated C-API functions but uses the new PyConfig API instead on CPython versions that support it (3.8+). Patch by Alexander Shadchin. (Github issue 4895)
  • Intel C compilers could complain about unsupported gcc pragmas. Patch by Ralf Gommers. (Github issue 5052)
  • Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.33 release.

Other changes

  • The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was removed. The type modifier is not needed here and a plain cimport of the name will do. (Github issue 4904)
  • C-style array declarations (cdef int a[4]) are now (silently) deprecated in favour of the Java-style cdef int[4] a form. The latter was always available and the Python type declaration syntax already used it exclusively (a: int[4]). Patch by Matúš Valo. (Github issue 5248)
  • The wheel building process was migrated to use the cibuildwheel tool. Patch by Thomas Li. (Github issue 4736)
  • Wheels now include a compiled parser again, which increases their size a little but gives about a 10% speed-up when running Cython.
  • The Tempita module no longer contains HTML processing capabilities, which were found to be broken in Python 3.8 and later. Patch by Marcel Stimberg. (Github issue 3309)
  • The Emacs Cython mode file cython-mode.el is now maintained in a separate repo: https://github.com/cython/emacs-cython-mode
  • Cython now uses a .dev0 version suffix for unreleased source installations.

3.0.0 alpha 11 (2022-07-31)

Features added

  • A new decorator @cython.dataclasses.dataclass was implemented that provides compile time dataclass generation capabilities to cdef classes (extension types). Patch by David Woods. (Github issue 2903). kw_only dataclasses added by Yury Sokov. (Github issue 4794)
  • Named expressions (PEP 572) aka. assignment expressions (aka. the walrus operator :=) were implemented. Patch by David Woods. (Github issue 2636)
  • Context managers can be written in parentheses. Patch by David Woods. (Github issue 4814)
  • Cython avoids raising StopIteration in __next__ methods when possible. Patch by David Woods. (Github issue 3447)
  • Some C++ and CPython library declarations were extended and fixed. Patches by Max Bachmann, Till Hoffmann, Julien Jerphanion, Wenjun Si. (Github issues 4530, 4528, 4710, 4746, 4751, 4818, 4762, 4910)
  • The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27. Patches by Evgeni Burovski and Eli Schwartz. (Github issue 1214)
  • cythonize() and the corresponding CLI command now regenerate the output files also when they already exist but were generated by a different Cython version.
  • Memory views and the internal Cython array type now identify as collections.abc.Sequence. Patch by David Woods. (Github issue 4817)
  • Cython generators and coroutines now identify as CO_ASYNC_GENERATOR, CO_COROUTINE and CO_GENERATOR accordingly. (Github issue 4902)
  • Memory views can use atomic CPU instructions instead of locks in more cases. Patch by Sam Gross. (Github issue 4912)
  • The environment variable CYTHON_FORCE_REGEN=1 can be used to force cythonize to regenerate the output files regardless of modification times and changes.
  • A new Cython build option --cython-compile-minimal was added to compile only a smaller set of Cython's own modules, which can be used to reduce the package and install size.
  • Improvements to PyTypeObject definitions in pxd wrapping of libpython. Patch by John Kirkham. (Github issue 4699)

Bugs fixed

  • Decorators like @cfunc and @ccall could leak into nested functions and classes. Patch by David Woods. (Github issue 4092)
  • Exceptions within for-loops that run over memoryviews could lead to a ref-counting error. Patch by David Woods. (Github issue 4662)
  • Using memoryview arguments in closures of inner functions could lead to ref-counting errors. Patch by David Woods. (Github issue 4798)
  • Several optimised string methods failed to accept None as arguments to their options. Test patch by Kirill Smelkov. (Github issue 4737)
  • A regression in 3.0.0a10 was resolved that prevented property setter methods from having the same name as their value argument. Patch by David Woods. (Github issue 4836)
  • Typedefs for the bint type did not always behave like bint. Patch by Nathan Manville and 0dminnimda. (Github issue 4660)
  • The return type of a fused function is no longer ignored for function pointers, since it is relevant when passing them e.g. as argument into other fused functions. Patch by David Woods. (Github issue 4644)
  • The __self__ attribute of fused functions reports its availability correctly with hasattr(). Patch by David Woods. (Github issue 4808)
  • pyximport no longer uses the deprecated imp module. Patch by Matúš Valo. (Github issue 4560)
  • pyximport failed for long filenames on Windows. Patch by Matti Picus. (Github issue 4630)
  • The generated C code failed to compile in CPython 3.11a4 and later. (Github issue 4500)
  • A case of undefined C behaviour was resolved in the list slicing code. Patch by Richard Barnes. (Github issue 4734)
  • Using the Limited API could report incorrect line numbers in tracebacks.
  • A work-around for StacklessPython < 3.8 was disabled in Py3.8 and later. (Github issue 4329)
  • Improve conversion between function pointers with non-identical but compatible exception specifications. Patches by David Woods. (Github issues 4770, 4689)
  • The runtime size check for imported PyVarObject types was improved to reduce false positives and adapt to Python 3.11. Patch by David Woods. (Github issues 4827, 4894)
  • The generated modules no longer import NumPy internally when using fused types but no memoryviews. Patch by David Woods. (Github issue 4935)
  • Improve compatibility with forthcoming CPython 3.12 release.
  • Limited API C preprocessor warning is compatible with MSVC. Patch by Victor Molina Garcia. (Github issue 4826)
  • Some C compiler warnings were fixed. Patch by mwtian. (Github issue 4831)
  • The parser allowed some invalid spellings of .... Patch by 0dminnimda. (Github issue 4868)
  • Includes all bug-fixes and features from the 0.29 maintenance branch up to the 0.29.32 release.

Other changes

  • When using type annotations, func(x: list) or func(x: ExtType) (and other Python builtin or extension types) no longer allow None as input argument to x. This is consistent with the normal typing semantics in Python, and was a common gotcha for users who did not expect None to be allowed as input. To allow None, use typing.Optional as in func(x: Optional[list]). None is also automatically allowed when it is used as default argument, i.e. func(x: list = None). int and float are now also recognised in type annotations and restrict the value type at runtime. They were previously ignored. Note that, for backwards compatibility reasons, the new behaviour does not apply when using Cython's C notation, as in func(list x). Here, None is still allowed, as always. Also, the annotation_typing directive can now be enabled and disabled more finely within the module. (Github issues 3883, 2696, 4669, 4606, 4886)
  • The compile-time DEF and IF statements are deprecated and generate a warning. They should be replaced with normal constants, code generation or C macros. (Github issue 4310)
  • Reusing an extension type attribute name as a method name is now an error. Patch by 0dminnimda. (Github issue 4661)
  • Improve compatibility between classes pickled in Cython 3.0 and 0.29.x by accepting MD5, SHA-1 and SHA-256 checksums. (Github issue 4680)

3.0.0 alpha 10 (2022-01-06)

Features added

  • Cython.Distutils.build_ext now uses cythonize() internally (previously known as new_build_ext), while still supporting the options that were available in the old implementation (old_build_ext). Patch by Matúš Valo. (Github issue 3541)
  • pyximport now uses cythonize() internally. Patch by Matúš Valo. (Github issue 2304)
  • __del__(self) on extension types now maps to tp_finalize in Python 3. Original patch by ax487. (Github issue 3612)
  • Conversion from Python dict to C++ map now supports arbitrary Python mappings, not just dicts.
  • Direct assignments to C++ references are now allowed. Patch by David Woods. (Github issue 1863)
  • An initial set of adaptations for GraalVM Python was implemented. Note that this does not imply any general support for this target or that your code will work at all in this environment. But testing should be possible now. Patch by David Woods. (Github issue 4328)
  • PyMem_[Raw]Calloc() was added to the cpython.mem declarations. Note that the Raw versions are no longer #defined by Cython. The previous macros were not considered safe. Patch by William Schwartz and David Woods. (Github issue 3047)

Bugs fixed

  • Circular imports of compiled modules could fail needlessly even when the import could already be resolved from sys.modules. Patch by Syam Gadde. (Github issue 4390)
  • The GIL can now safely be released inside of nogil functions (which may actually be called with the GIL held at runtime). Patch by David Woods. (Github issue 4137)
  • Type errors when passing memory view arguments could leak buffer references. Patch by David Woods. (Github issue 4296)
  • Cython did not type the self argument in special binary methods. Patch by David Woods. (Github issue 4434)
  • An incompatibility with recent coverage.py versions was resolved. Patch by David Woods. (Github issue 4440)
  • Fused typed default arguments generated incorrect code. Patch by David Woods. (Github issue 4413)
  • prange loops generated incorrect code when cpp_locals is enabled. Patch by David Woods. (Github issue 4354)
  • A C-level compatibility issue with recent NumPy versions was resolved. Patch by David Woods. (Github issue 4396)
  • Decorators on inner functions were not evaluated in the right scope. Patch by David Woods. (Github issue 4367)
  • Very early errors during module initialisation could lead to crashes. Patch by David Woods. (Github issue 4377)
  • Fused functions were binding unnecessarily, which prevented them from being pickled. Patch by David Woods. (Github issue 4370)
  • Some constant tuples containing strings were not deduplicated. Patch by David Woods. (Github issue 4353)
  • Unsupported decorators on cdef functions were not rejected in recent releases. Patch by David Woods. (Github issue 4322)
  • The excess arguments in a for-in-range loop with more than 3 arguments to range() were silently ignored. Original patch by Max Bachmann. (Github issue 4550)
  • Python object types were not allowed as -> return type annotations. Patch by Matúš Valo. (Github issue 4433)
  • Default values for memory views arguments were not properly supported. Patch by Corentin Cadiou. (Github issue 4313)
  • Templating C++ classes with memory view types lead to buggy code and is now rejected. Patch by David Woods. (Github issue 3085)
  • Several C++ library declarations were added and fixed. Patches by Dobatymo, account-login, Jonathan Helgert, Evgeny Yakimov, GalaxySnail, Max Bachmann. (Github issues 4408, 4419, 4410, 4395, 4423, 4448, 4462, 3293, 4522, 2171, 4531)
  • Some compiler problems and warnings were resolved. Patches by David Woods, 0dminnimda, Nicolas Pauss and others. (Github issues 4317, 4324, 4361, 4357)
  • The self argument of static methods in .pxd files was incorrectly typed. Patch by David Woods. (Github issue 3174)
  • A name collision when including multiple generated API header files was resolved. Patch by David Woods. (Github issue 4308)
  • An endless loop in cython-mode.el was resolved. Patch by Johannes Mueller. (Github issue 3218)
  • _Py_TPFLAGS_HAVE_VECTORCALL was always set on extension types when using the limited API. Patch by David Woods. (Github issue 4453)
  • Some compatibility issues with PyPy were resolved. Patches by Max Bachmann, Matti Picus. (Github issues 4454, 4477, 4478, 4509, 4517)
  • A compiler crash when running Cython thread-parallel from distutils was resolved. (Github issue 4503)
  • Includes all bug-fixes from the 0.29.26 release.

Other changes

  • A warning was added when __defaults__ or __kwdefaults__ of Cython compiled functions were re-assigned, since this does not current have an effect. Patch by David Woods. (Github issue 2650)

3.0.0 alpha 9 (2021-07-21)

Features added

  • Declarations for libcpp.algorithms, libcpp.set and libcpp.unordered_set were extended. Patch by David Woods. (Github issues 4271, 4273)
  • cygdb has a new option --skip-interpreter that allows using a different Python runtime than the one used to generate the debugging information. Patch by Alessandro Molina. (Github issue 4186)

Bugs fixed

  • Several issues with the new cpp_locals directive were resolved and its test coverage improved. Patch by David Woods. (Github issues 4266, 4265)
  • Generated utility code for C++ conversions no longer depends on several user definable directives that may make it behave incorrectly. Patch by David Woods. (Github issue 4206)
  • A reference counting bug in the new @cython.total_ordering decorator was fixed.
  • Includes all bug-fixes from the 0.29.24 release.

Other changes

  • Parts of the documentation were (and are being) rewritten to show the Cython language syntax next to the equivalent Python syntax. Patches by 0dminnimda and Matúš Valo. (Github issue 4187)

3.0.0 alpha 8 (2021-07-02)

Features added

  • A @cython.total_ordering decorator has been added to automatically implement all comparison operators, similar to functools.total_ordering. Patch by Spencer Brown. (Github issue 2090)
  • A new directive cpp_locals was added that allows local C++ variables to be lazily initialised (without default constructor), thus making them behave more like Python variables. Patch by David Woods. (Github issue 4160)
  • C++17 execution policies are supported in libcpp.algorithm. Patch by Ashwin Srinath. (Github issue 3790)
  • New C feature flags: CYTHON_USE_MODULE_STATE, CYTHON_USE_TYPE_SPECS Both are currently considered experimental. (Github issue 3611)
  • [...] * N is optimised for C integer multipliers N. (Github issue 3922)

Bugs fixed

  • The dispatch code for binary operators to special methods could run into infinite recursion. Patch by David Woods. (Github issue 4172)
  • Code optimisations were not applied to methods of Cython implemented C++ classes. Patch by David Woods. (Github issue 4212)
  • The special cython module was not always detected in PEP-484 type annotations. Patch by David Woods. (Github issue 4243)
  • Conversion from Python dicts to std::map was broken. Patch by David Woods and Mikkel Skofelt. (Github issues 4231, 4228)
  • The exception handling annotation except +* was broken. Patch by David Woods. (Github issues 3065, 3066)
  • Attribute annotations in Python classes are now ignored, because they are just Python objects in a dict (as opposed to the fields of extension types). Patch by David Woods. (Github issues 4196, 4198)
  • An unnecessary slow-down at import time was removed from Cython.Distutils. Original patch by Anthony Sottile. (Github issue 4224)
  • Python modules were not automatically recompiled when only their .pxd file changed. Patch by Golden Rockefeller. (Github issue 1428)
  • The signature of PyFloat_FromString() in cpython.float was changed to match the signature in Py3. It still has an automatic fallback for Py2. (Github issue 3909)
  • A compile error on MSVC was resolved. Patch by David Woods. (Github issue 4202)
  • A C compiler warning in PyPy3 regarding PyEval_EvalCode() was resolved.
  • Directives starting with optimization.* in pure Python mode were incorrectly named. It should have been optimize.*. Patch by David Woods. (Github issue 4258)

Other changes

  • Variables can no longer be declared with cpdef. Patch by David Woods. (Github issue 887)
  • Support for the now unsupported Pyston V1 was removed in favour of Pyston V2. Patch by Marius Wachtler. (Github issue 4211)
  • The Cython.Build.BuildExecutable tool no longer executes the program automatically. Use cythonrun for that.

3.0.0 alpha 7 (2021-05-24)

Features added

  • A cimport is now supported in pure Python code by prefixing the imported module name with cython.cimports., e.g. from cython.cimports.libc.math import sin. (GIthub issue 4190)
  • __class_getitem__ (PEP-560) is supported for cdef classes. Patch by Kmol Yuan. (Github issue 3764)
  • __mro_entries__ (PEP-560) is supported for Python classes. Patch by David Woods. (Github issue 3537)
  • cython.array supports simple, non-strided views. (Github issue 3775)
  • Self-documenting f-strings (=) were implemented. Patch by davfsa. (Github issue 3796)
  • The destructor is now called for fields in C++ structs. Patch by David Woods. (Github issue 3226)
  • std::move() is now also called for temps during yield. Patch by Yu Feng. (Github issue 4154)
  • asyncio.iscoroutinefunction() now recognises coroutine functions also when compiled by Cython. Patch by Pedro Marques da Luz. (Github issue 2273)
  • C compiler warnings and errors are now shown in Jupyter notebooks. Patch by Egor Dranischnikow. (Github issue 3751)
  • float(…) is optimised for string arguments (str/bytes/bytearray).
  • Converting C++ containers to Python lists uses less memory allocations. Patch by Max Bachmann. (Github issue 4081)
  • Docstrings of cpdef enums are now copied to the enum class. Patch by matham. (Github issue 3805)
  • The type cython.Py_hash_t is available in Python mode.
  • C-API declarations for cpython.fileobject were added. Patch by Zackery Spytz. (Github issue 3906)
  • C-API declarations for context variables in Python 3.7 were added. Original patch by Zolisa Bleki. (Github issue 2281)
  • More C-API declarations for cpython.datetime were added. Patch by Bluenix2. (Github issue 4128)
  • A new module cpython.time was added with some low-level alternatives to Python's time module. Patch by Brock Mendel. (Github issue 3767)
  • The value PyBUF_MAX_NDIM was added to the cpython.buffer module. Patch by John Kirkham. (Github issue 3811)
  • "Declaration after use" is now an error for variables. Patch by David Woods. (Github issue 3976)
  • More declarations for C++ string methods were added.
  • Cython now detects when existing output files were not previously generated by itself and refuses to overwrite them. It is a common mistake to name the module file of a wrapper after the library (source file) that it wraps, which can lead to surprising errors when the file gets overwritten.

Bugs fixed

  • Annotations were not exposed on annotated (data-)classes. Patch by matsjoyce. (Github issue 4151)
  • Inline functions and other code in .pxd files could accidentally inherit the compiler directives of the .pyx file that imported them. Patch by David Woods. (Github issue 1071)
  • Some issues were resolved that could lead to duplicated C names. Patch by David Woods. (Github issue 3716, 3741, 3734)
  • Modules with unicode names failed to build on Windows. Patch by David Woods. (Github issue 4125)
  • ndarray.shape failed to compile with Pythran and recent NumPy. Patch by Serge Guelton. (Github issue 3762)
  • Casting to ctuples is now allowed. Patch by David Woods. (Github issue 3808)
  • Structs could not be instantiated with positional arguments in pure Python mode.
  • Literal list assignments to pointer variables declared in PEP-526 notation failed to compile.
  • Nested C++ types were not usable through ctypedefs. Patch by Vadim Pushtaev. (Github issue 4039)
  • Overloaded C++ static methods were lost. Patch by Ashwin Srinath. (Github 1851)
  • Cython compiled functions always provided a __self__ attribute, regardless of being used as a method or not. Patch by David Woods. (Github issue 4036)
  • Calls to .__class__() of a known extension type failed. Patch by David Woods. (Github issue 3954)
  • Generator expressions in pxd-overridden cdef functions could fail to compile. Patch by Matúš Valo. (Github issue 3477)
  • A reference leak on import failures was resolved. Patch by Max Bachmann. (Github issue 4056)
  • A C compiler warning about unused code was resolved. (Github issue 3763)
  • A C compiler warning about enum value casting was resolved in GCC. (Github issue 2749)
  • Some C compiler warninge were resolved. Patches by Max Bachmann. (Github issue 4053, 4059, 4054, 4148, 4162)
  • A compile failure for C++ enums in Py3.4 / MSVC was resolved. Patch by Ashwin Srinath. (Github issue 3782)
  • Some C++ STL methods did not propagate exceptions. Patch by Max Bachmann. (Github issue 4079)
  • An unsupported C-API call in PyPy was fixed. Patch by Max Bachmann. (Github issue 4055)
  • The Cython CodeWriter mishandled no-argument return statements. Patch by Tao He. (Github issue 3795)
  • complex wasn't supported in PEP-484 type annotations. Patch by David Woods. (Github issue 3949)
  • Default arguments of methods were not exposed for introspection. Patch by Vladimir Matveev. (Github issue 4061)
  • Extension types inheriting from Python classes could not safely be exposed in .pxd files. (Github issue 4106)
  • The profiling/tracing code was adapted to work with Python 3.10b1.
  • The internal CPython macro Py_ISSPACE() is no longer used. Original patch by Andrew Jones. (Github issue 4111)
  • Includes all bug-fixes from the 0.29.23 release.

3.0.0 alpha 6 (2020-07-31)

Features added

  • Special methods for binary operators now follow Python semantics. Rather than e.g. a single __add__ method for cdef classes, where "self" can be either the first or second argument, one can now define both __add__ and __radd__ as for standard Python classes. This behavior can be disabled with the c_api_binop_methods directive to return to the previous semantics in Cython code (available from Cython 0.29.20), or the reversed method (__radd__) can be implemented in addition to an existing two-sided operator method (__add__) to get a backwards compatible implementation. (Github issue 2056)
  • No/single argument functions now accept keyword arguments by default in order to comply with Python semantics. The marginally faster calling conventions METH_NOARGS and METH_O that reject keyword arguments are still available with the directive @cython.always_allow_keywords(False). (Github issue 3090)
  • For-in-loop iteration over bytearray and memory views is optimised. Patch by David Woods. (Github issue 2227)
  • Type inference now works for memory views and slices. Patch by David Woods. (Github issue 2227)
  • The @returns() decorator propagates exceptions by default for suitable C return types when no @exceptval() is defined. (Github issues 3625, 3664)
  • A low-level inline function total_seconds(timedelta) was added to cpython.datetime to bypass the Python method call. Note that this function is not guaranteed to give exactly the same results for very large time intervals. Patch by Brock Mendel. (Github issue 3616)
  • Type inference now understands that a, *b = x assigns a list to b.
  • Limited API support was improved. Patches by Matthias Braun. (Github issues 3693, 3707)
  • The Cython CodeWriter can now handle more syntax constructs. Patch by Tao He. (Github issue 3514)

Bugs fixed

  • The construct for x in cpp_function_call() failed to compile. Patch by David Woods. (Github issue 3663)
  • C++ references failed to compile when used as Python object indexes. Patch by David Woods. (Github issue 3754)
  • The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue 3637)
  • repr() was assumed to return str instead of unicode with language_level=3. (Github issue 3736)
  • Includes all bug-fixes from the 0.29.21 release.

Other changes

  • The numpy declarations were updated. Patch by Brock Mendel. (Github issue 3630)
  • The names of Cython's internal types (functions, generator, coroutine, etc.) are now qualified with the module name of the internal Cython module that is used for sharing them across Cython implemented modules, for example _cython_3_0a5.coroutine. This was done to avoid making them look like homeless builtins, to help with debugging, and in order to avoid a CPython warning according to https://bugs.python.org/issue20204

3.0.0 alpha 5 (2020-05-19)

Features added

  • .pxd files can now be versioned <versioning> by adding an extension like ".cython-30.pxd" to prevent older Cython versions (than 3.0 in this case) from picking them up. (Github issue 3577)
  • Several macros/functions declared in the NumPy API are now usable without holding the GIL.
  • libc.math was extended to include all C99 function declarations. Patch by Dean Scarff. (Github issue 3570)

Bugs fixed

  • Several issues with arithmetic overflow handling were resolved, including undefined behaviour in C. Patch by Sam Sneddon. (Github issue 3588)
  • The improved GIL handling in nogil functions introduced in 3.0a3 could fail to acquire the GIL in some cases on function exit. (Github issue 3590 etc.)
  • A reference leak when processing keyword arguments in Py2 was resolved, that appeared in 3.0a1. (Github issue 3578)
  • The outdated getbuffer/releasebuffer implementations in the NumPy declarations were removed so that buffers declared as ndarray now use the normal implementation in NumPy.
  • Includes all bug-fixes from the 0.29.18 release.

3.0.0 alpha 4 (2020-05-05)

Features added

  • The print statement (not the print() function) is allowed in nogil code without an explicit with gil section.
  • The assert statement is allowed in nogil sections. Here, the GIL is only acquired if the AssertionError is really raised, which means that the evaluation of the asserted condition only allows C expressions.
  • Cython generates C compiler branch hints for unlikely user defined if-clauses in more cases, when they end up raising exceptions unconditionally. This now includes exceptions being raised in nogil/with gil sections.
  • Some internal memoryview functions were tuned to reduce object overhead.

Bugs fixed

  • Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.
  • Error handling early in the module init code could lead to a crash.
  • Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.
  • Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue 1407)
  • When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue 2209)
  • The improved GIL handling in nogil functions introduced in 3.0a3 could generate invalid C code. (Github issue 3558)
  • PyEval_InitThreads() is no longer used in Py3.7+ where it is a no-op.
  • Parallel builds of Cython itself (setup.py build_ext -j N) failed on Windows.

Other changes

  • The C property feature has been rewritten and now requires C property methods to be declared inline (3571).

3.0.0 alpha 3 (2020-04-27)

Features added

  • nogil functions now avoid acquiring the GIL on function exit if possible even if they contain with gil blocks. (Github issue 3554)
  • Python private name mangling now falls back to unmangled names for non-Python globals, since double-underscore names are not uncommon in C. Unmangled Python names are also still found as a legacy fallback but produce a warning. Patch by David Woods. (Github issue 3548)

Bugs fixed

  • Includes all bug-fixes from the 0.29.17 release.

3.0.0 alpha 2 (2020-04-23)

Features added

  • std::move() is now used in C++ mode for internal temp variables to make them work without copying values. Patch by David Woods. (Github issues 3253, 1612)
  • __class_getitem__ is supported for types on item access (PEP-560). Patch by msg555. (Github issue 2753)
  • The simplified Py3.6 customisation of class creation is implemented (PEP-487). (Github issue 2781)
  • Conditional blocks in Python code that depend on cython.compiled are eliminated at an earlier stage, which gives more freedom in writing replacement Python code. Patch by David Woods. (Github issue 3507)
  • numpy.import_array() is automatically called if numpy has been cimported and it has not been called in the module code. This is intended as a hidden fail-safe so user code should continue to call numpy.import_array. Patch by David Woods. (Github issue 3524)
  • The Cython AST code serialiser class CodeWriter in Cython.CodeWriter supports more syntax nodes.
  • The fastcall/vectorcall protocols are used for several internal Python calls. (Github issue 3540)

Bugs fixed

  • With language_level=3/3str, Python classes without explicit base class are now new-style (type) classes also in Py2. Previously, they were created as old-style (non-type) classes. (Github issue 3530)
  • C++ typeid() failed for fused types. Patch by David Woods. (Github issue 3203)
  • __arg argument names in methods were not mangled with the class name. Patch by David Woods. (Github issue 1382)
  • Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3531)
  • Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3534)
  • Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues 3430, 3522)
  • Several C compiler warnings were fixed.

3.0.0 alpha 1 (2020-04-12)

Features added

  • Cython functions now use the PEP-590 vectorcall protocol in Py3.7+. Patch by Jeroen Demeyer. (Github issue 2263)
  • Unicode identifiers are supported in Cython code (PEP-3131). Patch by David Woods. (Github issue 2601)
  • Unicode module names and imports are supported. Patch by David Woods. (Github issue 3119)
  • Annotations are no longer parsed, keeping them as strings following PEP-563. Patch by David Woods. (Github issue 3285)
  • Preliminary support for the CPython's Py_LIMITED_API (stable ABI) is available by setting the CYTHON_LIMITED_API C macro. Note that the support is currently in an early stage and many features do not yet work. You currently still have to define Py_LIMITED_API externally in order to restrict the API usage. This will change when the feature stabilises. Patches by Eddie Elizondo and David Woods. (Github issues 3223, 3311, 3501)
  • The dispatch to fused functions is now linear in the number of arguments, which makes it much faster, often 2x or more, and several times faster for larger fused types with many specialisations. Patch by will-ca. (Github issue 1385)
  • with gil/nogil statements can be conditional based on compile-time constants, e.g. fused type checks. Patch by Noam Hershtig. (Github issue 2579)
  • const can be used together with fused types. Patch by Thomas Vincent. (Github issue 1772)
  • Reimports of already imported modules are substantially faster. (Github issue 2854)
  • Positional-only arguments are supported in Python functions (PEP-570). Patch by Josh Tobin. (Github issue 2915)
  • The volatile C modifier is supported in Cython code. Patch by Jeroen Demeyer. (Github issue 1667)
  • @cython.trashcan(True) can be used on an extension type to enable the CPython trashcan. This allows deallocating deeply recursive objects without overflowing the stack. Patch by Jeroen Demeyer. (Github issue 2842)
  • Inlined properties can be defined for external extension types. Patch by Matti Picus. (Github issue 2640, redone later in 3571)
  • The str() builtin now calls PyObject_Str() instead of going through a Python call. Patch by William Ayd. (Github issue 3279)
  • String concatenation can now happen in place if possible, by extending the existing string rather than always creating a new one. Patch by David Woods. (Github issue 3453)
  • Multiplication of Python numbers with small constant integers is faster. (Github issue 2808)
  • Some list copying is avoided internally when a new list needs to be created but we already have a fresh one. (Github issue 3494)
  • Extension types that do not need their own tp_new implementation (because they have no object attributes etc.) directly inherit the implementation of their parent type if possible. (Github issue 1555)
  • The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection. (Github issue 2306)
  • Several declarations in cpython.*, libc.* and libcpp.* were added. Patches by Jeroen Demeyer, Matthew Edwards, Chris Gyurgyik, Jerome Kieffer and Zackery Spytz. (Github issues 3468, 3332, 3202, 3188, 3179, 2891, 2826, 2713)
  • Deprecated NumPy API usages were removed from numpy.pxd. Patch by Matti Picus. (Github issue 3365)
  • cython.inline() now sets the NPY_NO_DEPRECATED_API=NPY_1_7_API_VERSION C macro automatically when numpy is imported in the code, to avoid C compiler warnings about deprecated NumPy C-API usage.
  • The builtin abs() function can now be used on C numbers in nogil code. Patch by Elliott Sales de Andrade. (Github issue 2748)
  • PEP-479 (generator_stop) is now enabled by default with language level 3. (Github issue 2580)
  • The cython.view.array type supports inheritance. Patch by David Woods. (Github issue 3413)
  • Code annotation accepts a new debugging argument --annotate-fullc that will include the complete syntax highlighted C file in the HTML output. (Github issue 2855)
  • --no-capture added to runtests.py to prevent stdout/stderr capturing during srctree tests. Patch by Matti Picus. (Github issue 2701)
  • --no-docstrings option added to cythonize script. Original patch by mo-han. (Github issue 2889)
  • cygdb gives better error messages when it fails to initialise the Python runtime support in gdb. Patch by Volker Weissmann. (Github issue 3489)
  • The Pythran shape attribute is supported. Patch by Serge Guelton. (Github issue 3307)

Bugs fixed

  • The unicode methods .upper(), .lower() and .title() were incorrectly optimised for single character input values and only returned the first character if multiple characters should have been returned. They now use the original Python methods again.
  • Fused argument types were not correctly handled in type annotations and cython.locals(). Patch by David Woods. (Github issues 3391, 3142)
  • Diverging from the usual behaviour, len(memoryview), len(char*) and len(Py_UNICODE*) returned an unsigned size_t value. They now return a signed Py_ssize_t, like other usages of len().
  • Nested dict literals in function call kwargs could incorrectly raise an error about duplicate keyword arguments, which are allowed when passing them from dict literals. (Github issue 2963)
  • Item access (subscripting) with integer indices/keys always tried the Sequence protocol before the Mapping protocol, which diverged from Python semantics. It now passes through the Mapping protocol first when supported. (Github issue 1807)
  • Name lookups in class bodies no longer go through an attribute lookup. Patch by Jeroen Demeyer. (Github issue 3100)
  • Broadcast assignments to a multi-dimensional memory view slice could end up in the wrong places when the underlying memory view is known to be contiguous but the slice is not. (Github issue 2941)
  • Pickling unbound methods of Python classes failed. Patch by Pierre Glaser. (Github issue 2972)
  • The Py_hash_t type failed to accept arbitrary "index" values. (Github issue 2752)
  • The first function line number of functions with decorators pointed to the signature line and not the first decorator line, as in Python. Patch by Felix Kohlgrüber. (Github issue 2536)
  • Constant integer expressions that used a negative exponent were evaluated as integer 0 instead of the expected float value. Patch by Kryštof Pilnáček. (Github issue 2133)
  • The cython.declare() and cython.cast() functions could fail in pure mode. Patch by Dmitry Shesterkin. (Github issue 3244)
  • __doc__ was not available inside of the class body during class creation. (Github issue 1635)
  • Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue 2791)
  • __init__.pyx files were not always considered as package indicators. (Github issue 2665)
  • Compiling package __init__ files could fail under Windows due to an undefined export symbol. (Github issue 2968)
  • A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue 2775)
  • Binding staticmethods of Cython functions were not behaving like Python methods. Patch by Jeroen Demeyer. (Github issue 3106, 3102)
  • Memoryviews failed to compile when the cache_builtins feature was disabled. Patch by David Woods. (Github issue 3406)

Other changes

  • The default language level was changed to 3str, i.e. Python 3 semantics, but with str literals (also in Python 2.7). This is a backwards incompatible change from the previous default of Python 2 semantics. The previous behaviour is available through the directive language_level=2. (Github issue 2565)
  • Cython no longer generates __qualname__ attributes for classes in Python 2.x since they are problematic there and not correctly maintained for subclasses. Patch by Jeroen Demeyer. (Github issue 2772)
  • Source file fingerprinting now uses SHA-1 instead of MD5 since the latter tends to be slower and less widely supported these days. (Github issue 2790)
  • The long deprecated include files python_*, stdio, stdlib and stl in Cython/Includes/Deprecated/ were removed. Use the libc.* and cpython.* pxd modules instead. Patch by Jeroen Demeyer. (Github issue 2904)
  • The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Patch by Matti Picus. (Github issue 2905)
  • The command line parser was rewritten and modernised using argparse. Patch by Egor Dranischnikow. (Github issue 2952, 3001)
  • Dotted filenames for qualified module names (pkg.mod.pyx) are deprecated. Use the normal Python package directory layout instead. (Github issue 2686)
  • Binary Linux wheels now follow the manylinux2010 standard. Patch by Alexey Stepanov. (Github issue 3355)
  • Support for Python 2.6 was removed.

0.29.37 (2023-12-18)

Bugs fixed

  • Fix a potential crash while cleaning up subtypes of externally imported extension types when terminating Python. This was introduced in Cython 0.29.35.
  • Fix a complex related compile error on Windows. (Github issue 5512)
  • Compiling fused types used in pxd files could crash Cython in Python 3.11+. (Github issues 5894, 5588)
  • cythonize failed to consider the CYTHON_FORCE_REGEN env variable. Patch by Harmen Stoppels. (Github issue 5712)

0.29.36 (2023-07-04)

Bugs fixed

  • Async generators lost their return value in PyPy. (Github issue 5465)
  • The outdated C macro _PyGC_FINALIZED() is no longer used in Py3.9+.
  • The deprecated Py_OptimizeFlag is no longer used in Python 3.9+. (Github issue 5343)
  • Using the global __debug__ variable but not assertions could lead to compile errors.
  • The broken HTML template support was removed from Tempita. (Github issue 3309)

0.29.35 (2023-05-24)

Bugs fixed

  • A garbage collection enabled subtype of a non-GC extension type could call into the deallocation function of the super type with GC tracking enabled. This could lead to crashes during deallocation if GC was triggered on the type at the same time. (Github issue 5432)
  • Some C compile failures and crashes in CPython 3.12 were resolved.
  • except + nogil was syntactically not allowed. except +nogil (i.e. defining a C++ exception handling function called nogil) is now disallowed to prevent typos. (Github issue 5430)
  • A C compile failure in PyPy 3.10 was resolved. Patch by Matti Picus. (Github issue 5408)
  • Cython modules now use PEP-489 multi-phase init by default in PyPy 3.9 and later. Original patch by Matti Picus. (Github issue 5413)
  • API header files generated by different Cython versions can now be included in the same C file. (Github issue 5383)
  • Function signatures containing a type like tuple[()] could not be printed. Patch by Lisandro Dalcin. (Github issue 5355)

0.29.34 (2023-04-02)

Bugs fixed

  • A reference leak of the for-loop list/tuple iterable was resolved if the for-loop's else: branch executes a break for an outer loop. (Github issue 5347)
  • Some C compile failures in CPython 3.12 were resolved.
  • Some old usages of the deprecated Python imp module were replaced with importlib. Patch by Matúš Valo. (Github issue 5300)
  • Some issues with depfile generation were resolved. Patches by Eli Schwartz. (Github issues 5279, 5291)

0.29.33 (2023-01-06)

Features added

  • The cythonize and cython commands have a new option -M / --depfile to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. The cythonize option was already available in Cython 0.29.27. Patches by Evgeni Burovski and Eli Schwartz. (Github issue 1214)

Bugs fixed

  • const fused types could not be used with memory views. Patch by Thomas Vincent. (Github issue 1772)
  • wstr usage was removed in Python 3.12 and later (PEP-623). (Github issue 5145)
  • A type check assertion for Cython functions failed in debug Python builds. (Github issue 5031)
  • Fixed various compiler warnings. Patches by Lisandro Dalcin et al. (Github issues 4948, 5086)
  • Fixed error when calculating complex powers of negative numbers. (Github issue 5014)
  • Corrected a small mis-formatting of exception messages on Python 2. (Github issue 5018)
  • The PyUnicode_AsUTF8AndSize() C-API function was missing from the CPython declarations. (Github issue 5163)
  • A performance problem in the compiler was resolved when nesting conditional expressions. (Github issue 5197)
  • Test suite problems with recent NumPy and CPython versions were resolved. (Github issues 5183, 5190)

Other changes

  • The undocumented, untested and apparently useless syntax from somemodule cimport class/struct/union somename was deprecated in anticipation of its removal in Cython 3. The type modifier is not needed here and a plain cimport of the name will do. (Github issue 4905)
  • Properly disable generation of descriptor docstrings on PyPy since they cause crashes. It was previously disabled, but only accidentally via a typo. Patch by Matti Picus. (Github issue 5083)
  • The cpow directive of Cython 3.0 is available as a no-op. (Github issue 5016)

0.29.32 (2022-07-29)

Bugs fixed

  • Revert "Using memoryview typed arguments in inner functions is now rejected as unsupported." Patch by David Woods. (Github issue 4798)
  • from module import * failed in 0.29.31 when using memoryviews. Patch by David Woods. (Github issue 4927)

0.29.31 (2022-07-27)

Features added

  • A new argument --module-name was added to the cython command to provide the (one) exact target module name from the command line. Patch by Matthew Brett and h-vetinari. (Github issue 4906)
  • A new keyword noexcept was added for forward compatibility with Cython 3. Patch by David Woods. (Github issue 4903)

Bugs fixed

  • Use importlib.util.find_spec() instead of the deprecated importlib.find_loader() function when setting up the package path at import-time. Patch by Matti Picus. (Github issue 4764)
  • Require the C compiler to support the two-arg form of va_start on Python 3.10 and higher. Patch by Thomas Caswell. (Github issue 4820)
  • Make fused_type subscriptable in Shadow.py. Patch by Pfebrer. (Github issue 4842)
  • Fix the incorrect code generation of the target type in bytearray loops. Patch by Kenrick Everett. (Github issue 4108)
  • Atomic refcounts for memoryviews were not used on some GCC versions by accident. Patch by Sam Gross. (Github issue 4915)
  • Silence some GCC -Wconversion warnings in C utility code. Patch by Lisandro Dalcin. (Github issue 4854)
  • Tuple multiplication was ignored in expressions such as [*(1,) * 2]. Patch by David Woods. (Github issue 4864)
  • Calling append methods on extension types could fail to find the method in some cases. Patch by David Woods. (Github issue 4828)
  • Ensure that object buffers (e.g. ndarray[object, ndim=1]) containing NULL pointers are safe to use, returning None instead of the NULL pointer. Patch by Sebastian Berg. (Github issue 4859)
  • Using memoryview typed arguments in inner functions is now rejected as unsupported. Patch by David Woods. (Github issue 4798)
  • Compilation could fail on systems (e.g. FIPS) that block MD5 checksums at runtime. (Github issue 4909)
  • Experimental adaptations for the CPython "nogil" fork was added. Note that there is no official support for this in Cython 0.x. Patch by Sam Gross. (Github issue 4912)

0.29.30 (2022-05-16)

Bugs fixed

  • The GIL handling changes in 0.29.29 introduced a regression where objects could be deallocated without holding the GIL. (Github issue 4796)

0.29.29 (2022-05-16)

Features added

  • Avoid acquiring the GIL at the end of nogil functions. This change was backported in order to avoid generating wrong C code that would trigger C compiler warnings with tracing support enabled. Backport by Oleksandr Pavlyk. (Github issue 4637)

Bugs fixed

  • Function definitions in finally: clauses were not correctly generated. Patch by David Woods. (Github issue 4651)
  • A case where C-API functions could be called with a live exception set was fixed. Patch by Jakub Kulík. (Github issue 4722)
  • Pickles can now be exchanged again with those generated from Cython 3.0 modules. (Github issue 4680)
  • Cython now correctly generates Python methods for both the provided regular and reversed special numeric methods of extension types. Patch by David Woods. (Github issue 4750)
  • Calling unbound extension type methods without arguments could raise an IndexError instead of a TypeError. Patch by David Woods. (Github issue 4779)
  • Calling unbound .__contains__() super class methods on some builtin base types could trigger an infinite recursion. Patch by David Woods. (Github issue 4785)
  • The C union type in pure Python mode mishandled some field names. Patch by Jordan Brière. (Github issue 4727)
  • Allow users to overwrite the C macro _USE_MATH_DEFINES. Patch by Yuriy Chernyshov. (Github issue 4690)
  • Improved compatibility with CPython 3.10/11. Patches by Thomas Caswell, David Woods. (Github issues 4609, 4667, 4721, 4730, 4777)
  • Docstrings of descriptors are now provided in PyPy 7.3.9. Patch by Matti Picus. (Github issue 4701)

0.29.28 (2022-02-17)

Bugs fixed

  • Due to backwards incompatible changes in CPython 3.11a4, the feature flags CYTHON_FAST_THREAD_STATE and CYTHON_USE_EXC_INFO_STACK are now disabled in Python 3.11 and later. They are enabled again in Cython 3.0. Patch by David Woods. (Github issue 4610)
  • A C compiler warning in older PyPy versions was resolved. Patch by Matti Picus. (Github issue 4236)

0.29.27 (2022-01-28)

Features added

  • The cythonize command has a new option -M to generate .dep dependency files for the compilation unit. This can be used by external build tools to track these dependencies. Patch by Evgeni Burovski. (Github issue 1214)

Bugs fixed

  • Compilation failures on PyPy were resolved. Patches by Matti Picus. (Github issues 4509, 4517)
  • Calls to range() with more than three arguments did not fail. Original patch by Max Bachmann. (Github issue 4550)
  • Some C compiler warnings about missing type struct initialisers in Py3.10 were resolved.
  • Cython no longer warns about using OpenMP 3.0 features since they are now considered generally available.

0.29.26 (2021-12-16)

Bugs fixed

  • An incompatibility with CPython 3.11.0a3 was resolved. (Github issue 4499)
  • The in operator failed on literal lists with starred expressions. Patch by Arvind Natarajan. (Github issue 3938)
  • A C compiler warning in PyPy about a missing struct field initialisation was resolved.

0.29.25 (2021-12-06)

Bugs fixed

  • Several incompatibilities with CPython 3.11 were resolved. Patches by David Woods, Victor Stinner, Thomas Caswell. (Github issues 4411, 4414, 4415, 4416, 4420, 4428, 4473, 4479, 4480)
  • Some C compiler warnings were resolved. Patches by Lisandro Dalcin and others. (Github issue 4439)
  • C++ std::move() should only be used automatically in MSVC versions that support it. Patch by Max Bachmann. (Github issue 4191)
  • The Py_hash_t type failed to accept arbitrary "index" values. (Github issue 2752)
  • Avoid copying unaligned 16-bit values since some platforms require them to be aligned. Use memcpy() instead to let the C compiler decide how to do it. (Github issue 4343)
  • Cython crashed on invalid truthiness tests on C++ types without operator bool. Patch by David Woods. (Github issue 4348)
  • The declaration of PyUnicode_CompareWithASCIIString() in cpython.unicode was incorrect. Patch by Max Bachmann. (Github issue 4344)

0.29.24 (2021-07-14)

Bugs fixed

  • Inline functions in pxd files that used memory views could lead to invalid C code if the module that imported from them does not use memory views. Patch by David Woods. (Github issue 1415)
  • Several declarations in libcpp.string were added and corrected. Patch by Janek Bevendorff. (Github issue 4268)
  • Pickling unbound Cython compiled methods failed. Patch by Pierre Glaser. (Github issue 2972)
  • The tracing code was adapted to work with CPython 3.10.
  • The optimised in operator failed on unicode strings in Py3.9 and later that were constructed from an external wchar_t source. Also, related C compiler warnings about deprecated C-API usage were resolved. (Github issue 3925)
  • Some compiler crashes were resolved. Patch by David Woods. (Github issues 4214, 2811)
  • An incorrect warning about 'unused' generator expressions was removed. (GIthub issue 1699)
  • The attributes gen.gi_frame and coro.cr_frame of Cython compiled generators and coroutines now return an actual frame object for introspection, instead of None. (Github issue 2306)

0.29.23 (2021-04-14)

Bugs fixed

  • Some problems with Python 3.10 were resolved. Patches by Victor Stinner and David Woods. (Github issues 4046, 4100)
  • An incorrect "optimisation" was removed that allowed changes to a keyword dict to leak into keyword arguments passed into a function. Patch by Peng Weikang. (Github issue 3227)
  • Multiplied str constants could end up as bytes constants with language_level=2. Patch by Alphadelta14 and David Woods. (Github issue 3951)
  • PY_SSIZE_T_CLEAN does not get defined any more if it is already defined. Patch by Andrew Jones. (Github issue 4104)

0.29.22 (2021-02-20)

Features added

  • Some declarations were added to the provided pxd includes. Patches by Zackery Spytz and John Kirkham. (Github issues 3811, 3882, 3899, 3901)

Bugs fixed

  • A crash when calling certain functions in Py3.9 and later was resolved. (Github issue 3917)
  • const memory views of structs failed to compile. (Github issue 2251)
  • const template declarations could not be nested. Patch by Ashwin Srinath. (Github issue 1355)
  • The declarations in the cpython.pycapsule module were missing their const modifiers and generated incorrect C code. Patch by Warren Weckesser. (Github issue 3964)
  • Casts to memory views failed for fused dtypes. Patch by David Woods. (Github issue 3881)
  • repr() was assumed to return str instead of unicode with language_level=3. (Github issue 3736)
  • Calling cpdef functions from cimported modules crashed the compiler. Patch by David Woods. (Github issue 4000)
  • Cython no longer validates the ABI size of the NumPy classes it compiled against. See the discussion in numpy/numpy#432
  • A C compiler warning about enum value casting was resolved in GCC. (Github issue 2749)
  • Coverage reporting in the annotated HTML file failed in Py3.9. Patch by Nick Pope. (Github issue 3865)
  • The embedding code now reports Python errors as exit status.
  • Long type declarations could lead to (harmless) random changes in the C file when used in auto-generated Python wrappers or pickled classes.

Other changes

  • Variables defined as cpdef now generate a warning since this is currently useless and thus does not do what users would expect. Patch by David Woods. (Github issue 3959)

0.29.21 (2020-07-09)

Bugs fixed

  • Fix a regression in 0.29.20 where __div__ failed to be found in extension types. (Github issue 3688)
  • Fix a regression in 0.29.20 where a call inside of a finally clause could fail to compile. Patch by David Woods. (Github issue 3712)
  • Zero-sized buffers could fail to validate as C/Fortran-contiguous. Patch by Clemens Hofreither. (Github issue 2093)
  • exec() did not allow recent Python syntax features in Py3.8+ due to https://bugs.python.org/issue35975. (Github issue 3695)
  • Binding staticmethods of Cython functions were not behaving like Python methods in Py3. Patch by Jeroen Demeyer and Michał Górny. (Github issue 3106)
  • Pythran calls to NumPy methods no longer generate useless method lookup code.
  • The PyUnicode_GET_LENGTH() macro was missing from the cpython.* declarations. Patch by Thomas Caswell. (Github issue 3692)
  • The deprecated PyUnicode_*() C-API functions are no longer used, except for Unicode strings that contain lone surrogates. Unicode strings that contain non-BMP characters or surrogate pairs now generate different C code on 16-bit Python 2.x Unicode deployments (such as MS-Windows). Generating the C code on Python 3.x is recommended in this case. Original patches by Inada Naoki and Victor Stinner. (Github issues 3677, 3721, 3697)
  • Some template parameters were missing from the C++ std::unordered_map declaration. Patch by will. (Github issue 3685)
  • Several internal code generation issues regarding temporary variables were resolved. (Github issue 3708)

0.29.20 (2020-06-10)

Bugs fixed

  • Nested try-except statements with multiple return statements could crash due to incorrect deletion of the except as target variable. (Github issue 3666)
  • The @classmethod decorator no longer rejects unknown input from other decorators. Patch by David Woods. (Github issue 3660)
  • Fused types could leak into unrelated usages. Patch by David Woods. (Github issue 3642)
  • Now uses Py_SET_SIZE() and Py_SET_REFCNT() in Py3.9+ to avoid low-level write access to these object fields. Patch by Victor Stinner. (Github issue 3639)
  • The built-in abs() function could lead to undefined behaviour when used on the negative-most value of a signed C integer type. Patch by Serge Guelton. (Github issue 1911)
  • Usages of sizeof() and typeid() on uninitialised variables no longer produce a warning. Patch by Celelibi. (Github issue 3575)
  • The C++ typeid() function was allowed in C mode. Patch by Celelibi. (Github issue 3637)
  • The error position reported for errors found in f-strings was misleading. (Github issue 3674)
  • The new c_api_binop_methods directive was added for forward compatibility, but can only be set to True (the current default value). It can be disabled in Cython 3.0.

0.29.19 (2020-05-20)

Bugs fixed

  • A typo in Windows specific code in 0.29.18 was fixed that broke "libc.math". (Github issue 3622)
  • A platform specific test failure in 0.29.18 was fixed. Patch by smutch. (Github issue 3620)

0.29.18 (2020-05-18)

Bugs fixed

  • Exception position reporting could run into race conditions on threaded code. It now uses function-local variables again.
  • Error handling early in the module init code could lead to a crash.
  • Error handling in cython.array creation was improved to avoid calling C-API functions with an error held.
  • A memory corruption was fixed when garbage collection was triggered during calls to PyType_Ready() of extension type subclasses. (Github issue 3603)
  • Memory view slicing generated unused error handling code which could negatively impact the C compiler optimisations for parallel OpenMP code etc. Also, it is now helped by static branch hints. (Github issue 2987)
  • Cython's built-in OpenMP functions were not translated inside of call arguments. Original patch by Celelibi and David Woods. (Github issue 3594)
  • Complex buffer item types of structs of arrays could fail to validate. Patch by Leo and smutch. (Github issue 1407)
  • Decorators were not allowed on nested async def functions. (Github issue 1462)
  • C-tuples could use invalid C struct casting. Patch by MegaIng. (Github issue 3038)
  • Optimised %d string formatting into f-strings failed on float values. (Github issue 3092)
  • Optimised aligned string formatting (%05s, %-5s) failed. (Github issue 3476)
  • When importing the old Cython build_ext integration with distutils, the additional command line arguments leaked into the regular command. Patch by Kamekameha. (Github issue 2209)
  • When using the CYTHON_NO_PYINIT_EXPORT option in C++, the module init function was not declared as extern "C". (Github issue 3414)
  • Three missing timedelta access macros were added in cpython.datetime.
  • The signature of the NumPy C-API function PyArray_SearchSorted() was fixed. Patch by Brock Mendel. (Github issue 3606)

0.29.17 (2020-04-26)

Features added

  • std::move() is now available from libcpp.utility. Patch by Omer Ozarslan. (Github issue 2169)
  • The @cython.binding decorator is available in Python code. (Github issue 3505)

Bugs fixed

  • Creating an empty unicode slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3531)
  • Decoding an empty bytes/char* slice with large bounds could crash. Patch by Sam Sneddon. (Github issue 3534)
  • Re-importing a Cython extension no longer raises the error "__reduce_cython__ not found". (Github issue 3545)
  • Unused C-tuples could generate incorrect code in 0.29.16. Patch by Kirk Meyer. (Github issue 3543)
  • Creating a fused function attached it to the garbage collector before it was fully initialised, thus risking crashes in rare failure cases. Original patch by achernomorov. (Github issue 3215)
  • Temporary buffer indexing variables were not released and could show up in C compiler warnings, e.g. in generators. Patch by David Woods. (Github issues 3430, 3522)
  • The compilation cache in cython.inline("…") failed to take the language level into account. Patch by will-ca. (Github issue 3419)
  • The deprecated PyUnicode_GET_SIZE() function is no longer used in Py3.

0.29.16 (2020-03-24)

Bugs fixed

  • Temporary internal variables in nested prange loops could leak into other threads. Patch by Frank Schlimbach. (Github issue 3348)
  • Default arguments on fused functions could crash. Patch by David Woods. (Github issue 3370)
  • C-tuples declared in .pxd files could generate incomplete C code. Patch by Kirk Meyer. (Github issue 1427)
  • Fused functions were not always detected and optimised as Cython implemented functions. Patch by David Woods. (Github issue 3384)
  • Valid Python object concatenation of (iterable) strings to non-strings could fail with an exception. Patch by David Woods. (Github issue 3433)
  • Using C functions as temporary values lead to invalid C code. Original patch by David Woods. (Github issue 3418)
  • Fix an unhandled C++ exception in comparisons. Patch by David Woods. (Github issue 3361)
  • Fix deprecated import of "imp" module. Patch by Matti Picus. (Github issue 3350)
  • Fix compatibility with Pythran 0.9.6 and later. Patch by Serge Guelton. (Github issue 3308)
  • The _Py_PyAtExit() function in cpython.pylifecycle was misdeclared. Patch by Zackery Spytz. (Github issue 3382)
  • Several missing declarations in cpython.* were added. Patches by Zackery Spytz. (Github issue 3452, 3421, 3411, 3402)
  • A declaration for libc.math.fpclassify() was added. Patch by Zackery Spytz. (Github issue 2514)
  • Avoid "undeclared" warning about automatically generated pickle methods. Patch by David Woods. (Github issue 3353)
  • Avoid C compiler warning about unreachable code in prange().
  • Some C compiler warnings in PyPy were resolved. Patch by Matti Picus. (Github issue 3437)

0.29.15 (2020-02-06)

Bugs fixed

  • Crash when returning a temporary Python object from an async-def function. (Github issue 3337)
  • Crash when using **kwargs in generators. Patch by David Woods. (Github issue 3265)
  • Double reference free in __class__ cell handling for super() calls. (Github issue 3246)
  • Compile error when using *args as Python class bases. (Github issue 3338)
  • Import failure in IPython 7.11. (Github issue 3297)
  • Fixed C name collision in the auto-pickle code. Patch by ThePrez. (Github issue 3238)
  • Deprecated import failed in Python 3.9. (Github issue 3266)

0.29.14 (2019-11-01)

Bugs fixed

  • The generated code failed to initialise the tp_print slot in CPython 3.8. Patches by Pablo Galindo and Orivej Desh. (Github issues 3171, 3201)
  • ? for bool was missing from the supported NumPy dtypes. Patch by Max Klein. (Github issue 2675)
  • await was not allowed inside of f-strings. Patch by Dmitro Getz. (Github issue 2877)
  • Coverage analysis failed for projects where the code resides in separate source sub-directories. Patch by Antonio Valentino. (Github issue 1985)
  • An incorrect compiler warning was fixed in automatic C++ string conversions. Patch by Gerion Entrup. (Github issue 3108)
  • Error reports in the Jupyter notebook showed unhelpful stack traces. Patch by Matthew Edwards (Github issue 3196).
  • Python.h is now also included explicitly from public header files. (Github issue 3133).
  • Distutils builds with --parallel did not work when using Cython's deprecated build_ext command. Patch by Alphadelta14 (Github issue 3187).

Other changes

  • The PyMemoryView_*() C-API is available in cpython.memoryview. Patch by Nathan Manville. (Github issue 2541)

0.29.13 (2019-07-26)

Bugs fixed

  • A reference leak for None was fixed when converting a memoryview to a Python object. (Github issue 3023)
  • The declaration of PyGILState_STATE in cpython.pystate was unusable. Patch by Kirill Smelkov. (Github issue 2997)

Other changes

  • The declarations in posix.mman were extended. Patches by Kirill Smelkov. (Github issues 2893, 2894, 3012)

0.29.12 (2019-07-07)

Bugs fixed

  • Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. (Github issue 3031)
  • Fix a C compiler warning about a missing int downcast. (Github issue 3028)
  • Fix reported error positions of undefined builtins and constants. Patch by Orivej Desh. (Github issue 3030)
  • A 32 bit issue in the Pythran support was resolved. Patch by Serge Guelton. (Github issue 3032)

0.29.11 (2019-06-30)

Bugs fixed

  • Fix compile error in CPython 3.8b2 regarding the PyCode_New() signature. Patch by Nick Coghlan. (Github issue 3009)
  • Invalid C code generated for lambda functions in cdef methods. Patch by Josh Tobin. (Github issue 2967)
  • Support slice handling in newer Pythran versions. Patch by Serge Guelton. (Github issue 2989)
  • A reference leak in power-of-2 calculation was fixed. Patch by Sebastian Berg. (Github issue 3022)
  • The search order for include files was changed. Previously it was include_directories, Cython/Includes, sys.path. Now it is include_directories, sys.path, Cython/Includes. This was done to allow third-party *.pxd files to override the ones in Cython. Original patch by Matti Picus. (Github issue 2905)
  • Setting language_level=2 in a file did not work if language_level=3 was enabled globally before. Patch by Jeroen Demeyer. (Github issue 2791)

0.29.10 (2019-06-02)

Bugs fixed

  • Fix compile errors in CPython 3.8b1 due to the new "tp_vectorcall" slots. (Github issue 2976)

0.29.9 (2019-05-29)

Bugs fixed

  • Fix a crash regression in 0.29.8 when creating code objects fails.
  • Remove an incorrect cast when using true-division in C++ operations. (Github issue 1950)

0.29.8 (2019-05-28)

Bugs fixed

  • C compile errors with CPython 3.8 were resolved. Patch by Marcel Plch. (Github issue 2938)
  • Python tuple constants that compare equal but have different item types could incorrectly be merged into a single constant. (Github issue 2919)
  • Non-ASCII characters in unprefixed strings could crash the compiler when used with language level 3str.
  • Starred expressions in %-formatting tuples could fail to compile for unicode strings. (Github issue 2939)
  • Passing Python class references through cython.inline() was broken. (Github issue 2936)

0.29.7 (2019-04-14)

Bugs fixed

  • Crash when the shared Cython config module gets unloaded and another Cython module reports an exceptions. Cython now makes sure it keeps an owned reference to the module. (Github issue 2885)
  • Resolved a C89 compilation problem when enabling the fast-gil sharing feature.
  • Coverage reporting did not include the signature line of cdef functions. (Github issue 1461)
  • Casting a GIL-requiring function into a nogil function now issues a warning. (Github issue 2879)
  • Generators and coroutines were missing their return type annotation. (Github issue 2884)

0.29.6 (2019-02-27)

Bugs fixed

  • Fix a crash when accessing the __kwdefaults__ special attribute of fused functions. (Github issue 1470)
  • Fix the parsing of buffer format strings that contain numeric sizes, which could lead to incorrect input rejections. (Github issue 2845)
  • Avoid a C #pragma in old gcc versions that was only added in GCC 4.6. Patch by Michael Anselmi. (Github issue 2838)
  • Auto-encoding of Unicode strings to UTF-8 C/C++ strings failed in Python 3, even though the default encoding there is UTF-8. (Github issue 2819)

0.29.5 (2019-02-09)

Bugs fixed

  • Crash when defining a Python subclass of an extension type and repeatedly calling a cpdef method on it. (Github issue 2823)
  • Compiler crash when prange() loops appear inside of with-statements. (Github issue 2780)
  • Some C compiler warnings were resolved. Patches by Christoph Gohlke. (Github issues 2815, 2816, 2817, 2822)
  • Python conversion of C++ enums failed in 0.29. Patch by Orivej Desh. (Github issue 2767)

0.29.4 (2019-02-01)

Bugs fixed

  • Division of numeric constants by a runtime value of 0 could fail to raise a ZeroDivisionError. (Github issue 2820)

0.29.3 (2019-01-19)

Bugs fixed

  • Some C code for memoryviews was generated in a non-deterministic order. Patch by Martijn van Steenbergen. (Github issue 2779)
  • C89 compatibility was accidentally lost since 0.28. Patches by gastineau and true-pasky. (Github issues 2778, 2801)
  • A C compiler cast warning was resolved. Patch by Michael Buesch. (Github issue 2774)
  • An compilation failure with complex numbers under MSVC++ was resolved. (Github issue 2797)
  • Coverage reporting could fail when modules were moved around after the build. Patch by Wenjun Si. (Github issue 2776)

0.29.2 (2018-12-14)

Bugs fixed

  • The code generated for deduplicated constants leaked some references. (Github issue 2750)
  • The declaration of sigismember() in libc.signal was corrected. (Github issue 2756)
  • Crashes in compiler and test runner were fixed. (Github issue 2736, 2755)
  • A C compiler warning about an invalid safety check was resolved. (Github issue 2731)

0.29.1 (2018-11-24)

Bugs fixed

  • Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue 2670)
  • Cython no longer requires the source to be writable when copying its data into a memory view slice. Patch by Andrey Paramonov. (Github issue 2644)
  • Line tracing of try-statements generated invalid C code. (Github issue 2274)
  • When using the warn.undeclared directive, Cython's own code generated warnings that are now fixed. Patch by Nicolas Pauss. (Github issue 2685)
  • Cython's memoryviews no longer require strides for setting the shape field but only the PyBUF_ND flag to be set. Patch by John Kirkham. (Github issue 2716)
  • Some C compiler warnings about unused memoryview code were fixed. Patch by Ho Cheuk Ting. (Github issue 2588)
  • A C compiler warning about implicit signed/unsigned conversion was fixed. (Github issue 2729)
  • Assignments to C++ references returned by operator[] could fail to compile. (Github issue 2671)
  • The power operator and the support for NumPy math functions were fixed in Pythran expressions. Patch by Serge Guelton. (Github issues 2702, 2709)
  • Signatures with memory view arguments now show the expected type when embedded in docstrings. Patch by Matthew Chan and Benjamin Weigel. (Github issue 2634)
  • Some from ... cimport ... constructs were not correctly considered when searching modified dependencies in cythonize() to decide whether to recompile a module. Patch by Kryštof Pilnáček. (Github issue 2638)
  • A struct field type in the cpython.array declarations was corrected. Patch by John Kirkham. (Github issue 2712)

0.29 (2018-10-14)

Features added

  • PEP-489 multi-phase module initialisation has been enabled again. Module reloads in other subinterpreters raise an exception to prevent corruption of the static module state.
  • A set of mypy compatible PEP-484 declarations were added for Cython's C data types to integrate with static analysers in typed Python code. They are available in the Cython/Shadow.pyi module and describe the types in the special cython module that can be used for typing in Python code. Original patch by Julian Gethmann. (Github issue 1965)
  • Memoryviews are supported in PEP-484/526 style type declarations. (Github issue 2529)
  • @cython.nogil is supported as a C-function decorator in Python code. (Github issue 2557)
  • Raising exceptions from nogil code will automatically acquire the GIL, instead of requiring an explicit with gil block.
  • C++ functions can now be declared as potentially raising both C++ and Python exceptions, so that Cython can handle both correctly. (Github issue 2615)
  • cython.inline() supports a direct language_level keyword argument that was previously only available via a directive.
  • A new language level name 3str was added that mostly corresponds to language level 3, but keeps unprefixed string literals as type 'str' in both Py2 and Py3, and the builtin 'str' type unchanged. This will become the default in the next Cython release and is meant to help user code a) transition more easily to this new default and b) migrate to Python 3 source code semantics without making support for Python 2.x difficult.
  • In CPython 3.6 and later, looking up globals in the module dict is almost as fast as looking up C globals. (Github issue 2313)
  • For a Python subclass of an extension type, repeated method calls to non-overridden cpdef methods can avoid the attribute lookup in Py3.6+, which makes them 4x faster. (Github issue 2313)
  • (In-)equality comparisons of objects to integer literals are faster. (Github issue 2188)
  • Some internal and 1-argument method calls are faster.
  • Modules that cimport many external extension types from other Cython modules execute less import requests during module initialisation.
  • Constant tuples and slices are deduplicated and only created once per module. (Github issue 2292)
  • The coverage plugin considers more C file extensions such as .cc and .cxx. (Github issue 2266)
  • The cythonize command accepts compile time variable values (as set by DEF) through the new -E option. Patch by Jerome Kieffer. (Github issue 2315)
  • pyximport can import from namespace packages. Patch by Prakhar Goel. (Github issue 2294)
  • Some missing numpy and CPython C-API declarations were added. Patch by John Kirkham. (Github issues 2523, 2520, 2537)
  • Declarations for the pylifecycle C-API functions were added in a new .pxd file cpython.pylifecycle.
  • The Pythran support was updated to work with the latest Pythran 0.8.7. Original patch by Adrien Guinet. (Github issue 2600)
  • %a is included in the string formatting types that are optimised into f-strings. In this case, it is also automatically mapped to %r in Python 2.x.
  • New C macro CYTHON_HEX_VERSION to access Cython's version in the same style as PY_VERSION_HEX.
  • Constants in libc.math are now declared as const to simplify their handling.
  • An additional check_size clause was added to the ctypedef class name specification to allow suppressing warnings when importing modules with backwards-compatible PyTypeObject size changes. Patch by Matti Picus. (Github issue 2627)

Bugs fixed

  • The exception handling in generators and coroutines under CPython 3.7 was adapted to the newly introduced exception stack. Users of Cython 0.28 who want to support Python 3.7 are encouraged to upgrade to 0.29 to avoid potentially incorrect error reporting and tracebacks. (Github issue 1958)
  • Crash when importing a module under Stackless Python that was built for CPython. Patch by Anselm Kruis. (Github issue 2534)
  • 2-value slicing of typed sequences failed if the start or stop index was None. Patch by Christian Gibson. (Github issue 2508)
  • Multiplied string literals lost their factor when they are part of another constant expression (e.g. 'x' * 10 + 'y' => 'xy').
  • String formatting with the '%' operator didn't call the special __rmod__() method if the right side is a string subclass that implements it. (Python issue 28598)
  • The directive language_level=3 did not apply to the first token in the source file. (Github issue 2230)
  • Overriding cpdef methods did not work in Python subclasses with slots. Note that this can have a performance impact on calls from Cython code. (Github issue 1771)
  • Fix declarations of builtin or C types using strings in pure python mode. (Github issue 2046)
  • Generator expressions and lambdas failed to compile in @cfunc functions. (Github issue 459)
  • Global names with const types were not excluded from star-import assignments which could lead to invalid C code. (Github issue 2621)
  • Several internal function signatures were fixed that lead to warnings in gcc-8. (Github issue 2363)
  • The numpy helper functions set_array_base() and get_array_base() were adapted to the current numpy C-API recommendations. Patch by Matti Picus. (Github issue 2528)
  • Some NumPy related code was updated to avoid deprecated API usage. Original patch by jbrockmendel. (Github issue 2559)
  • Several C++ STL declarations were extended and corrected. Patch by Valentin Valls. (Github issue 2207)
  • C lines of the module init function were unconditionally not reported in exception stack traces. Patch by Jeroen Demeyer. (Github issue 2492)
  • When PEP-489 support is enabled, reloading the module overwrote any static module state. It now raises an exception instead, given that reloading is not actually supported.
  • Object-returning, C++ exception throwing functions were not checking that the return value was non-null. Original patch by Matt Wozniski (Github issue 2603)
  • The source file encoding detection could get confused if the c_string_encoding directive appeared within the first two lines. (Github issue 2632)
  • Cython generated modules no longer emit a warning during import when the size of the NumPy array type is larger than what was found at compile time. Instead, this is assumed to be a backwards compatible change on NumPy side.

Other changes

  • Cython now emits a warning when no language_level (2, 3 or '3str') is set explicitly, neither as a cythonize() option nor as a compiler directive. This is meant to prepare the transition of the default language level from currently Py2 to Py3, since that is what most new users will expect these days. The future default will, however, not enforce unicode literals, because this has proven a major obstacle in the support for both Python 2.x and 3.x. The next major release is intended to make this change, so that it will parse all code that does not request a specific language level as Python 3 code, but with str literals. The language level 2 will continue to be supported for an indefinite time.
  • The documentation was restructured, cleaned up and examples are now tested. The NumPy tutorial was also rewritten to simplify the running example. Contributed by Gabriel de Marmiesse. (Github issue 2245)
  • Cython compiles less of its own modules at build time to reduce the installed package size to about half of its previous size. This makes the compiler slightly slower, by about 5-7%.

0.28.6 (2018-11-01)

Bugs fixed

  • Extensions compiled with MinGW-64 under Windows could misinterpret integer objects larger than 15 bit and return incorrect results. (Github issue 2670)
  • Multiplied string literals lost their factor when they are part of another constant expression (e.g. 'x' * 10 + 'y' => 'xy').

0.28.5 (2018-08-03)

Bugs fixed

  • The discouraged usage of GCC's attribute optimize("Os") was replaced by the similar attribute cold to reduce the code impact of the module init functions. (Github issue 2494)
  • A reference leak in Py2.x was fixed when comparing str to unicode for equality.

0.28.4 (2018-07-08)

Bugs fixed

  • Reallowing tp_clear() in a subtype of an @no_gc_clear extension type generated an invalid C function call to the (non-existent) base type implementation. (Github issue 2309)
  • Exception catching based on a non-literal (runtime) tuple could fail to match the exception. (Github issue 2425)
  • Compile fix for CPython 3.7.0a2. (Github issue 2477)

0.28.3 (2018-05-27)

Bugs fixed

  • Set iteration was broken in non-CPython since 0.28.
  • UnicodeEncodeError in Py2 when %s formatting is optimised for unicode strings. (Github issue 2276)
  • Work around a crash bug in g++ 4.4.x by disabling the size reduction setting of the module init function in this version. (Github issue 2235)
  • Crash when exceptions occur early during module initialisation. (Github issue 2199)

0.28.2 (2018-04-13)

Features added

  • abs() is faster for Python long objects.
  • The C++11 methods front() and end() were added to the declaration of libcpp.string. Patch by Alex Huszagh. (Github issue 2123)
  • The C++11 methods reserve() and bucket_count() are declared for libcpp.unordered_map. Patch by Valentin Valls. (Github issue 2168)

Bugs fixed

  • The copy of a read-only memoryview was considered read-only as well, whereas a common reason to copy a read-only view is to make it writable. The result of the copying is now a writable buffer by default. (Github issue 2134)
  • The switch statement generation failed to apply recursively to the body of converted if-statements.
  • NULL was sometimes rejected as exception return value when the returned type is a fused pointer type. Patch by Callie LeFave. (Github issue 2177)
  • Fixed compatibility with PyPy 5.11. Patch by Matti Picus. (Github issue 2165)

Other changes

  • The NumPy tutorial was rewritten to use memoryviews instead of the older buffer declaration syntax. Contributed by Gabriel de Marmiesse. (Github issue 2162)

0.28.1 (2018-03-18)

Bugs fixed

  • PyFrozenSet_New() was accidentally used in PyPy where it is missing from the C-API.
  • Assignment between some C++ templated types were incorrectly rejected when the templates mix const with ctypedef. (Github issue 2148)
  • Undeclared C++ no-args constructors in subclasses could make the compilation fail if the base class constructor was declared without nogil. (Github issue 2157)
  • Bytes %-formatting inferred basestring (bytes or unicode) as result type in some cases where bytes would have been safe to infer. (Github issue 2153)
  • None was accidentally disallowed as typed return value of dict.pop(). (Github issue 2152)

0.28 (2018-03-13)

Features added

  • Cdef classes can now multiply inherit from ordinary Python classes. (The primary base must still be a c class, possibly object, and the other bases must not be cdef classes.)
  • Type inference is now supported for Pythran compiled NumPy expressions. Patch by Nils Braun. (Github issue 1954)
  • The const modifier can be applied to memoryview declarations to allow read-only buffers as input. (Github issues 1605, 1869)
  • C code in the docstring of a cdef extern block is copied verbatimly into the generated file. Patch by Jeroen Demeyer. (Github issue 1915)
  • When compiling with gcc, the module init function is now tuned for small code size instead of whatever compile flags were provided externally. Cython now also disables some code intensive optimisations in that function to further reduce the code size. (Github issue 2102)
  • Decorating an async coroutine with @cython.iterable_coroutine changes its type at compile time to make it iterable. While this is not strictly in line with PEP-492, it improves the interoperability with old-style coroutines that use yield from instead of await.
  • The IPython magic has preliminary support for JupyterLab. (Github issue 1775)
  • The new TSS C-API in CPython 3.7 is supported and has been backported. Patch by Naotoshi Seo. (Github issue 1932)
  • Cython knows the new Py_tss_t type defined in PEP-539 and automatically initialises variables declared with that type to Py_tss_NEEDS_INIT, a value which cannot be used outside of static assignments.
  • The set methods .remove() and .discard() are optimised. Patch by Antoine Pitrou. (Github issue 2042)
  • dict.pop() is optimised. Original patch by Antoine Pitrou. (Github issue 2047)
  • Iteration over sets and frozensets is optimised. (Github issue 2048)
  • Safe integer loops (< range(2^30)) are automatically optimised into C loops.
  • alist.extend([a,b,c]) is optimised into sequential list.append() calls for short literal sequences.
  • Calls to builtin methods that are not specifically optimised into C-API calls now use a cache that avoids repeated lookups of the underlying C function. (Github issue 2054)
  • Single argument function calls can avoid the argument tuple creation in some cases.
  • Some redundant extension type checks are avoided.
  • Formatting C enum values in f-strings is faster, as well as some other special cases.
  • String formatting with the '%' operator is optimised into f-strings in simple cases.
  • Subscripting (item access) is faster in some cases.
  • Some bytearray operations have been optimised similar to bytes.
  • Some PEP-484/526 container type declarations are now considered for loop optimisations.
  • Indexing into memoryview slices with view[i][j] is now optimised into view[i, j].
  • Python compatible cython.* types can now be mixed with type declarations in Cython syntax.
  • Name lookups in the module and in classes are faster.
  • Python attribute lookups on extension types without instance dict are faster.
  • Some missing signals were added to libc/signal.pxd. Patch by Jeroen Demeyer. (Github issue 1914)
  • The warning about repeated extern declarations is now visible by default. (Github issue 1874)
  • The exception handling of the function types used by CPython's type slot functions was corrected to match the de-facto standard behaviour, so that code that uses them directly benefits from automatic and correct exception propagation. Patch by Jeroen Demeyer. (Github issue 1980)
  • Defining the macro CYTHON_NO_PYINIT_EXPORT will prevent the module init function from being exported as symbol, e.g. when linking modules statically in an embedding setup. Patch by AraHaan. (Github issue 1944)

Bugs fixed

  • If a module name is explicitly provided for an Extension() that is compiled via cythonize(), it was previously ignored and replaced by the source file name. It can now be used to override the target module name, e.g. for compiling prefixed accelerator modules from Python files. (Github issue 2038)
  • The arguments of the num_threads parameter of parallel sections were not sufficiently validated and could lead to invalid C code. (Github issue 1957)
  • Catching exceptions with a non-trivial exception pattern could call into CPython with a live exception set. This triggered incorrect behaviour and crashes, especially in CPython 3.7.
  • The signature of the special __richcmp__() method was corrected to recognise the type of the first argument as self. It was previously treated as plain object, but CPython actually guarantees that it always has the correct type. Note: this can change the semantics of user code that previously relied on self being untyped.
  • Some Python 3 exceptions were not recognised as builtins when running Cython under Python 2.
  • Some async helper functions were not defined in the generated C code when compiling simple async code. (Github issue 2075)
  • Line tracing did not include generators and coroutines. (Github issue 1949)
  • C++ declarations for unordered_map were corrected. Patch by Michael Schatzow. (Github issue 1484)
  • Iterator declarations in C++ deque and vector were corrected. Patch by Alex Huszagh. (Github issue 1870)
  • The const modifiers in the C++ string declarations were corrected, together with the coercion behaviour of string literals into C++ strings. (Github issue 2132)
  • Some declaration types in libc.limits were corrected. Patch by Jeroen Demeyer. (Github issue 2016)
  • @cython.final was not accepted on Python classes with an @cython.cclass decorator. (Github issue 2040)
  • Cython no longer creates useless and incorrect PyInstanceMethod wrappers for methods in Python 3. Patch by Jeroen Demeyer. (Github issue 2105)
  • The builtin bytearray type could not be used as base type of cdef classes. (Github issue 2106)

Other changes

0.27.3 (2017-11-03)

Bugs fixed

  • String forward references to extension types like @cython.locals(x="ExtType") failed to find the named type. (Github issue 1962)
  • NumPy slicing generated incorrect results when compiled with Pythran. Original patch by Serge Guelton (Github issue 1946).
  • Fix "undefined reference" linker error for generators on Windows in Py3.3-3.5. (Github issue 1968)
  • Adapt to recent C-API change of PyThreadState in CPython 3.7.
  • Fix signature of PyWeakref_GetObject() API declaration. Patch by Jeroen Demeyer (Github issue 1975).

0.27.2 (2017-10-22)

Bugs fixed

  • Comprehensions could incorrectly be optimised away when they appeared in boolean test contexts. (Github issue 1920)
  • The special methods __eq__, __lt__ etc. in extension types did not type their first argument as the type of the class but object. (Github issue 1935)
  • Crash on first lookup of "cline_in_traceback" option during exception handling. (Github issue 1907)
  • Some nested module level comprehensions failed to compile. (Github issue 1906)
  • Compiler crash on some complex type declarations in pure mode. (Github issue 1908)
  • std::unordered_map.erase() was declared with an incorrect void return type in libcpp.unordered_map. (Github issue 1484)
  • Invalid use of C++ fallthrough attribute before C++11 and similar issue in clang. (Github issue 1930)
  • Compiler crash on misnamed properties. (Github issue 1905)

0.27.1 (2017-10-01)

Features added

  • The Jupyter magic has a new debug option --verbose that shows details about the distutils invocation. Patch by Boris Filippov (Github issue 1881).

Bugs fixed

  • Py3 list comprehensions in class bodies resulted in invalid C code. (Github issue 1889)
  • Modules built for later CPython 3.5.x versions failed to import in 3.5.0/3.5.1. (Github issue 1880)
  • Deallocating fused types functions and methods kept their GC tracking enabled, which could potentially lead to recursive deallocation attempts.
  • Crash when compiling in C++ mode with old setuptools versions. (Github issue 1879)
  • C++ object arguments for the constructor of Cython implemented C++ are now passed by reference and not by value to allow for non-copyable arguments, such as unique_ptr.
  • API-exported C++ classes with Python object members failed to compile. (Github issue 1866)
  • Some issues with the new relaxed exception value handling were resolved.
  • Python classes as annotation types could prevent compilation. (Github issue 1887)
  • Cython annotation types in Python files could lead to import failures with a "cython undefined" error. Recognised types are now turned into strings.
  • Coverage analysis could fail to report on extension modules on some platforms.
  • Annotations could be parsed (and rejected) as types even with annotation_typing=False.

Other changes

  • PEP 489 support has been disabled by default to counter incompatibilities with import setups that try to reload or reinitialise modules.

0.27 (2017-09-23)

Features added

  • Extension module initialisation follows PEP 489 in CPython 3.5+, which resolves several differences with regard to normal Python modules. This makes the global names __file__ and __path__ correctly available to module level code and improves the support for module-level relative imports. (Github issues 1715, 1753, 1035)
  • Asynchronous generators (PEP 525) and asynchronous comprehensions (PEP 530) have been implemented. Note that async generators require finalisation support in order to allow for asynchronous operations during cleanup, which is only available in CPython 3.6+. All other functionality has been backported as usual.
  • Variable annotations are now parsed according to PEP 526. Cython types (e.g. cython.int) are evaluated as C type declarations and everything else as Python types. This can be disabled with the directive annotation_typing=False. Note that most complex PEP-484 style annotations are currently ignored. This will change in future releases. (Github issue 1850)
  • Extension types (also in pure Python mode) can implement the normal special methods __eq__, __lt__ etc. for comparisons instead of the low-level __richcmp__ method. (Github issue 690)
  • New decorator @cython.exceptval(x=None, check=False) that makes the signature declarations except x, except? x and except * available to pure Python code. Original patch by Antonio Cuni. (Github issue 1653)
  • Signature annotations are now included in the signature docstring generated by the embedsignature directive. Patch by Lisandro Dalcin (Github issue 1781).
  • The gdb support for Python code (libpython.py) was updated to the latest version in CPython 3.7 (git rev 5fe59f8).
  • The compiler tries to find a usable exception return value for cdef functions with except * if the returned type allows it. Note that this feature is subject to safety limitations, so it is still better to provide an explicit declaration.
  • C functions can be assigned to function pointers with a compatible exception declaration, not only with exact matches. A side-effect is that certain compatible signature overrides are now allowed and some more mismatches of exception signatures are now detected and rejected as errors that were not detected before.
  • The IPython/Jupyter magic integration has a new option %%cython --pgo for profile guided optimisation. It compiles the cell with PGO settings for the C compiler, executes it to generate a runtime profile, and then compiles it again using that profile for C compiler optimisation. Currently only tested with gcc.
  • len(memoryview) can be used in nogil sections to get the size of the first dimension of a memory view (shape[0]). (Github issue 1733)
  • C++ classes can now contain (properly refcounted) Python objects.
  • NumPy dtype subarrays are now accessible through the C-API. Patch by Gerald Dalley (Github issue 245).
  • Resolves several issues with PyPy and uses faster async slots in PyPy3. Patch by Ronan Lamy (Github issues 1871, 1878).

Bugs fixed

  • Extension types that were cimported from other Cython modules could disagree about the order of fused cdef methods in their call table. This could lead to wrong methods being called and potentially also crashes. The fix required changes to the ordering of fused methods in the call table, which may break existing compiled modules that call fused cdef methods across module boundaries, if these methods were implemented in a different order than they were declared in the corresponding .pxd file. (Github issue 1873)
  • The exception state handling in generators and coroutines could lead to exceptions in the caller being lost if an exception was raised and handled inside of the coroutine when yielding. (Github issue 1731)
  • Loops over range(enum) were not converted into C for-loops. Note that it is still recommended to use an explicit cast to a C integer type in this case.
  • Error positions of names (e.g. variables) were incorrectly reported after the name and not at the beginning of the name.
  • Compile time DEF assignments were evaluated even when they occur inside of falsy IF blocks. (Github issue 1796)
  • Disabling the line tracing from a trace function could fail. Original patch by Dmitry Trofimov. (Github issue 1769)
  • Several issues with the Pythran integration were resolved.
  • abs(signed int) now returns a signed rather than unsigned int. (Github issue 1837)
  • Reading frame.f_locals of a Cython function (e.g. from a debugger or profiler could modify the module globals. (Github issue 1836)
  • Buffer type mismatches in the NumPy buffer support could leak a reference to the buffer owner.
  • Using the "is_f_contig" and "is_c_contig" memoryview methods together could leave one of them undeclared. (Github issue 1872)
  • Compilation failed if the for-in-range loop target was not a variable but a more complex expression, e.g. an item assignment. (Github issue 1831)
  • Compile time evaluations of (partially) constant f-strings could show incorrect results.
  • Escape sequences in raw f-strings (fr'...') were resolved instead of passing them through as expected.
  • Some ref-counting issues in buffer error handling have been resolved.

Other changes

  • Type declarations in signature annotations are now parsed according to PEP 484 typing. Only Cython types (e.g. cython.int) and Python builtin types are currently considered as type declarations. Everything else is ignored, but this will change in a future Cython release. (Github issue 1672)
  • The directive annotation_typing is now True by default, which enables parsing type declarations from annotations.
  • This release no longer supports Python 3.2.

0.26.1 (2017-08-29)

Features added

Bugs fixed

  • cython.view.array was missing .__len__().
  • Extension types with a .pxd override for their __releasebuffer__ slot (e.g. as provided by Cython for the Python array.array type) could leak a reference to the buffer owner on release, thus not freeing the memory. (Github issue 1638)
  • Auto-decoding failed in 0.26 for strings inside of C++ containers. (Github issue 1790)
  • Compile error when inheriting from C++ container types. (Github issue 1788)
  • Invalid C code in generators (declaration after code). (Github issue 1801)
  • Arithmetic operations on const integer variables could generate invalid code. (Github issue 1798)
  • Local variables with names of special Python methods failed to compile inside of closures. (Github issue 1797)
  • Problem with indirect Emacs buffers in cython-mode. Patch by Martin Albrecht (Github issue 1743).
  • Extension types named result or PickleError generated invalid unpickling code. Patch by Jason Madden (Github issue 1786).
  • Bazel integration failed to compile .py files. Patch by Guro Bokum (Github issue 1784).
  • Some include directories and dependencies were referenced with their absolute paths in the generated files despite lying within the project directory.
  • Failure to compile in Py3.7 due to a modified signature of _PyCFunctionFast()

0.26 (2017-07-19)

Features added

  • Pythran can be used as a backend for evaluating NumPy array expressions. Patch by Adrien Guinet (Github issue 1607).
  • cdef classes now support pickling by default when possible. This can be disabled with the auto_pickle directive.
  • Speed up comparisons of strings if their hash value is available. Patch by Claudio Freire (Github issue 1571).
  • Support pyximport from zip files. Patch by Sergei Lebedev (Github issue 1485).
  • IPython magic now respects the __all__ variable and ignores names with leading-underscore (like import * does). Patch by Syrtis Major (Github issue 1625).
  • abs() is optimised for C complex numbers. Patch by David Woods (Github issue 1648).
  • The display of C lines in Cython tracebacks can now be enabled at runtime via import cython_runtime; cython_runtime.cline_in_traceback=True. The default has been changed to False.
  • The overhead of calling fused types generic functions was reduced.
  • "cdef extern" include files are now also searched relative to the current file. Patch by Jeroen Demeyer (Github issue 1654).
  • Optional optimization for re-acquiring the GIL, controlled by the fast_gil directive.

Bugs fixed

  • Item lookup/assignment with a unicode character as index that is typed (explicitly or implicitly) as Py_UCS4 or Py_UNICODE used the integer value instead of the Unicode string value. Code that relied on the previous behaviour now triggers a warning that can be disabled by applying an explicit cast. (Github issue 1602)
  • f-string processing was adapted to changes in PEP 498 and CPython 3.6.
  • Invalid C code when decoding from UTF-16(LE/BE) byte strings. (Github issue 1696)
  • Unicode escapes in 'ur' raw-unicode strings were not resolved in Py2 code. Original patch by Aaron Gallagher (Github issue 1594).
  • File paths of code objects are now relative. Original patch by Jelmer Vernooij (Github issue 1565).
  • Decorators of cdef class methods could be executed twice. Patch by Jeroen Demeyer (Github issue 1724).
  • Dict iteration using the Py2 iter* methods failed in PyPy3. Patch by Armin Rigo (Github issue 1631).
  • Several warnings in the generated code are now suppressed.

Other changes

  • The unraisable_tracebacks option now defaults to True.
  • Coercion of C++ containers to Python is no longer automatic on attribute access (Github issue 1521).
  • Access to Python attributes of cimported modules without the corresponding import is now a compile-time (rather than runtime) error.
  • Do not use special dll linkage for "cdef public" functions. Patch by Jeroen Demeyer (Github issue 1687).
  • cdef/cpdef methods must match their declarations. See Github issue 1732. This is now a warning and will be an error in future releases.

0.25.2 (2016-12-08)

Bugs fixed

  • Fixes several issues with C++ template deduction.
  • Fixes a issue with bound method type inference (Github issue 551).
  • Fixes a bug with cascaded tuple assignment (Github issue 1523).
  • Fixed or silenced many Clang warnings.
  • Fixes bug with powers of pure real complex numbers (Github issue 1538).

0.25.1 (2016-10-26)

Bugs fixed

  • Fixes a bug with isinstance(o, Exception) (Github issue 1496).
  • Fixes bug with cython.view.array missing utility code in some cases (Github issue 1502).

Other changes

  • The distutils extension Cython.Distutils.build_ext has been reverted, temporarily, to be old_build_ext to give projects time to migrate. The new build_ext is available as new_build_ext.

0.25 (2016-10-25)

Features added

  • def/cpdef methods of cdef classes benefit from Cython's internal function implementation, which enables introspection and line profiling for them. Implementation sponsored by Turbostream (www.turbostream-cfd.com).
  • Calls to Python functions are faster, following the recent "FastCall" optimisations that Victor Stinner implemented for CPython 3.6. See https://bugs.python.org/issue27128 and related issues.
  • The new METH_FASTCALL calling convention for PyCFunctions is supported in CPython 3.6. See https://bugs.python.org/issue27810
  • Initial support for using Cython modules in Pyston. Patch by Boxiang Sun.
  • Dynamic Python attributes are allowed on cdef classes if an attribute cdef dict __dict__ is declared in the class. Patch by empyrical.
  • Cython implemented C++ classes can make direct calls to base class methods. Patch by empyrical.
  • C++ classes can now have typedef members. STL containers updated with value_type.
  • New directive cython.no_gc to fully disable GC for a cdef class. Patch by Claudio Freire.
  • Buffer variables are no longer excluded from locals(). Patch by David Woods.
  • Building f-strings is faster, especially when formatting C integers.
  • for-loop iteration over "std::string".
  • libc/math.pxd provides e and pi as alias constants to simplify usage as a drop-in replacement for Python's math module.
  • Speed up cython.inline().
  • Binary lshift operations with small constant Python integers are faster.
  • Some integer operations on Python long objects are faster in Python 2.7.
  • Support for the C++ typeid operator.
  • Support for bazel using a the pyx_library rule in //Tools:rules.bzl.

Significant Bugs fixed

  • Division of complex numbers avoids overflow by using Smith's method.
  • Some function signatures in libc.math and numpy.pxd were incorrect. Patch by Michael Seifert.

Other changes

  • The "%%cython" IPython/jupyter magic now defaults to the language level of the current jupyter kernel. The language level can be set explicitly with "%%cython -2" or "%%cython -3".
  • The distutils extension Cython.Distutils.build_ext has now been updated to use cythonize which properly handles dependencies. The old extension can still be found in Cython.Distutils.old_build_ext and is now deprecated.
  • directive_defaults is no longer available in Cython.Compiler.Options, use get_directive_defaults() instead.

0.24.1 (2016-07-15)

Bugs fixed

  • IPython cell magic was lacking a good way to enable Python 3 code semantics. It can now be used as "%%cython -3".
  • Follow a recent change in PEP 492 and CPython 3.5.2 that now requires the __aiter__() method of asynchronous iterators to be a simple def method instead of an async def method.
  • Coroutines and generators were lacking the __module__ special attribute.
  • C++ std::complex values failed to auto-convert from and to Python complex objects.
  • Namespaced C++ types could not be used as memory view types due to lack of name mangling. Patch by Ivan Smirnov.
  • Assignments between identical C++ types that were declared with differently typedefed template types could fail.
  • Rebuilds could fail to evaluate dependency timestamps in C++ mode. Patch by Ian Henriksen.
  • Macros defined in the distutils compiler option do not require values anymore. Patch by Ian Henriksen.
  • Minor fixes for MSVC, Cygwin and PyPy.

0.24 (2016-04-04)

Features added

  • PEP 498: Literal String Formatting (f-strings). Original patch by Jelle Zijlstra.
  • PEP 515: Underscores as visual separators in number literals.
  • Parser was adapted to some minor syntax changes in Py3.6, e.g. https://bugs.python.org/issue9232
  • The embedded C code comments that show the original source code can be discarded with the new directive emit_code_comments=False.
  • Cpdef enums are now first-class iterable, callable types in Python.
  • Ctuples can now be declared in pure Python code.
  • Posix declarations for DLL loading and stdio extensions were added. Patch by Lars Buitinck.
  • The Py2-only builtins unicode(), xrange(), reduce() and long are now also available in compile time DEF expressions when compiling with Py3.
  • Exception type tests have slightly lower overhead. This fixes ticket 868.
  • @property syntax fully supported in cdef classes, old syntax deprecated.
  • C++ classes can now be declared with default template parameters.

Bugs fixed

  • C++ exceptions raised by overloaded C++ operators were not always handled. Patch by Ian Henriksen.
  • C string literals were previously always stored as non-const global variables in the module. They are now stored as global constants when possible, and otherwise as non-const C string literals in the generated code that uses them. This improves compatibility with strict C compiler options and prevents non-const strings literals with the same content from being incorrectly merged.
  • Compile time evaluated str expressions (DEF) now behave in a more useful way by turning into Unicode strings when compiling under Python 3. This allows using them as intermediate values in expressions. Previously, they always evaluated to bytes objects.
  • isinf() declarations in libc/math.pxd and numpy/math.pxd now reflect the actual tristate int return value instead of using bint.
  • Literal assignments to ctuples avoid Python tuple round-trips in some more corner cases.
  • Iteration over dict(...).items() failed to get optimised when dict arguments included keyword arguments.
  • cProfile now correctly profiles cpdef functions and methods.

0.23.5 (2016-03-26)

  • Compile errors and warnings in integer type conversion code. This fixes ticket 877. Patches by Christian Neukirchen, Nikolaus Rath, Ian Henriksen.
  • Reference leak when *args argument was reassigned in closures.
  • Truth-testing Unicode strings could waste time and memory in Py3.3+.
  • Return values of async functions could be ignored and replaced by None.
  • Compiler crash in CPython 3.6.
  • Fix prange() to behave identically to range(). The end condition was miscalculated when the range was not exactly divisible by the step.
  • Optimised all(genexpr)/any(genexpr) calls could warn about unused code. This fixes ticket 876.

0.23.4 (2015-10-10)

Bugs fixed

  • Memory leak when calling Python functions in PyPy.
  • Compilation problem with MSVC in C99-ish mode.
  • Warning about unused values in a helper macro.

0.23.3 (2015-09-29)

Bugs fixed

  • Invalid C code for some builtin methods. This fixes ticket 856 again.
  • Incorrect C code in helper functions for PyLong conversion and string decoding. This fixes ticket 863, ticket 864 and ticket 865. Original patch by Nikolaus Rath.
  • Large folded or inserted integer constants could use too small C integer types and thus trigger a value wrap-around.

Other changes

  • The coroutine and generator types of Cython now also register directly with the Coroutine and Generator ABCs in the backports_abc module if it can be imported. This fixes ticket 870.

0.23.2 (2015-09-11)

Bugs fixed

  • Compiler crash when analysing some optimised expressions.
  • Coverage plugin was adapted to coverage.py 4.0 beta 2.
  • C++ destructor calls could fail when '&' operator is overwritten.
  • Incorrect C literal generation for large integers in compile-time evaluated DEF expressions and constant folded expressions.
  • Byte string constants could end up as Unicode strings when originating from compile-time evaluated DEF expressions.
  • Invalid C code when caching known builtin methods. This fixes ticket 860.
  • ino_t in posix.types was not declared as unsigned.
  • Declarations in libcpp/memory.pxd were missing operator!(). Patch by Leo Razoumov.
  • Static cdef methods can now be declared in .pxd files.

0.23.1 (2015-08-22)

Bugs fixed

  • Invalid C code for generators. This fixes ticket 858.
  • Invalid C code for some builtin methods. This fixes ticket 856.
  • Invalid C code for unused local buffer variables. This fixes ticket 154.
  • Test failures on 32bit systems. This fixes ticket 857.
  • Code that uses from xyz import * and global C struct/union/array variables could fail to compile due to missing helper functions. This fixes ticket 851.
  • Misnamed PEP 492 coroutine property cr_yieldfrom renamed to cr_await to match CPython.
  • Missing deallocation code for C++ object attributes in certain extension class hierarchies.
  • Crash when async coroutine was not awaited.
  • Compiler crash on yield in signature annotations and default argument values. Both are forbidden now.
  • Compiler crash on certain constructs in finally clauses.
  • Cython failed to build when CPython's pgen is installed.

0.23 (2015-08-08)

Features added

  • PEP 492 (async/await) was implemented.
  • PEP 448 (Additional Unpacking Generalizations) was implemented.
  • Support for coverage.py 4.0+ can be enabled by adding the plugin "Cython.Coverage" to the ".coveragerc" config file.
  • Annotated HTML source pages can integrate (XML) coverage reports.
  • Tracing is supported in nogil functions/sections and module init code.
  • When generators are used in a Cython module and the module imports the modules "inspect" and/or "asyncio", Cython enables interoperability by patching these modules during the import to recognise Cython's internal generator and coroutine types. This can be disabled by C compiling the module with "-D CYTHON_PATCH_ASYNCIO=0" or "-D CYTHON_PATCH_INSPECT=0"
  • When generators or coroutines are used in a Cython module, their types are registered with the Generator and Coroutine ABCs in the collections or collections.abc stdlib module at import time to enable interoperability with code that needs to detect and process Python generators/coroutines. These ABCs were added in CPython 3.5 and are available for older Python versions through the backports_abc module on PyPI. See https://bugs.python.org/issue24018
  • Adding/subtracting/dividing/modulus and equality comparisons with constant Python floats and small integers are faster.
  • Binary and/or/xor/rshift operations with small constant Python integers are faster.
  • When called on generator expressions, the builtins all(), any(), dict(), list(), set(), sorted() and unicode.join() avoid the generator iteration overhead by inlining a part of their functionality into the for-loop.
  • Keyword argument dicts are no longer copied on function entry when they are not being used or only passed through to other function calls (e.g. in wrapper functions).
  • The PyTypeObject declaration in cpython.object was extended.
  • The builtin type type is now declared as PyTypeObject in source, allowing for extern functions taking type parameters to have the correct C signatures. Note that this might break code that uses type just for passing around Python types in typed variables. Removing the type declaration provides a backwards compatible fix.
  • wraparound() and boundscheck() are available as no-ops in pure Python mode.
  • Const iterators were added to the provided C++ STL declarations.
  • Smart pointers were added to the provided C++ STL declarations. Patch by Daniel Filonik.
  • NULL is allowed as default argument when embedding signatures. This fixes ticket 843.
  • When compiling with --embed, the internal module name is changed to __main__ to allow arbitrary program names, including those that would be invalid for modules. Note that this prevents reuse of the generated C code as an importable module.
  • External C++ classes that overload the assignment operator can be used. Patch by Ian Henriksen.
  • Support operator bool() for C++ classes so they can be used in if statements.

Bugs fixed

  • Calling "yield from" from Python on a Cython generator that returned a value triggered a crash in CPython. This is now being worked around. See https://bugs.python.org/issue23996
  • Language level 3 did not enable true division (a.k.a. float division) for integer operands.
  • Functions with fused argument types that included a generic 'object' fallback could end up using that fallback also for other explicitly listed object types.
  • Relative cimports could accidentally fall back to trying an absolute cimport on failure.
  • The result of calling a C struct constructor no longer requires an intermediate assignment when coercing to a Python dict.
  • C++ exception declarations with mapping functions could fail to compile when pre-declared in .pxd files.
  • cpdef void methods are now permitted.
  • abs(cint) could fail to compile in MSVC and used sub-optimal code in C++. Patch by David Vierra, original patch by Michael Enßlin.
  • Buffer index calculations using index variables with small C integer types could overflow for large buffer sizes. Original patch by David Vierra.
  • C unions use a saner way to coerce from and to Python dicts.
  • When compiling a module foo.pyx, the directories in sys.path are no longer searched when looking for foo.pxd. Patch by Jeroen Demeyer.
  • Memory leaks in the embedding main function were fixed. Original patch by Michael Enßlin.
  • Some complex Python expressions could fail to compile inside of finally clauses.
  • Unprefixed 'str' literals were not supported as C varargs arguments.
  • Fixed type errors in conversion enum types to/from Python. Note that this imposes stricter correctness requirements on enum declarations.

Other changes

  • Changed mangling scheme in header files generated by cdef api declarations.
  • Installation under CPython 3.3+ no longer requires a pass of the 2to3 tool. This also makes it possible to run Cython in Python 3.3+ from a source checkout without installing it first. Patch by Petr Viktorin.
  • jedi-typer.py (in Tools/) was extended and renamed to jedityper.py (to make it importable) and now works with and requires Jedi 0.9. Patch by Tzer-jen Wei.

0.22.1 (2015-06-20)

Bugs fixed

  • Crash when returning values on generator termination.
  • In some cases, exceptions raised during internal isinstance() checks were not propagated.
  • Runtime reported file paths of source files (e.g for profiling and tracing) are now relative to the build root directory instead of the main source file.
  • Tracing exception handling code could enter the trace function with an active exception set.
  • The internal generator function type was not shared across modules.
  • Comparisons of (inferred) ctuples failed to compile.
  • Closures inside of cdef functions returning void failed to compile.
  • Using const C++ references in intermediate parts of longer expressions could fail to compile.
  • C++ exception declarations with mapping functions could fail to compile when pre-declared in .pxd files.
  • C++ compilation could fail with an ambiguity error in recent MacOS-X Xcode versions.
  • C compilation could fail in pypy3.
  • Fixed a memory leak in the compiler when compiling multiple modules.
  • When compiling multiple modules, external library dependencies could leak into later compiler runs. Fix by Jeroen Demeyer. This fixes ticket 845.

0.22 (2015-02-11)

Features added

  • C functions can coerce to Python functions, which allows passing them around as callable objects.
  • C arrays can be assigned by value and auto-coerce from Python iterables and to Python lists (and tuples).
  • Extern C functions can now be declared as cpdef to export them to the module's Python namespace. Extern C functions in pxd files export their values to their own module, iff it exists.
  • Anonymous C tuple types can be declared as (ctype1, ctype2, ...).
  • PEP 479: turn accidental StopIteration exceptions that exit generators into a RuntimeError, activated with future import "generator_stop".
  • Looping over reversed(range()) is optimised in the same way as range(). Patch by Favian Contreras.

Bugs fixed

  • Mismatching 'except' declarations on signatures in .pxd and .pyx files failed to produce a compile error.
  • Failure to find any files for the path pattern(s) passed into cythonize() is now an error to more easily detect accidental typos.
  • The logaddexp family of functions in numpy.math now has correct declarations.
  • In Py2.6/7 and Py3.2, simple Cython memory views could accidentally be interpreted as non-contiguous by CPython, which could trigger a CPython bug when copying data from them, thus leading to data corruption. See CPython issues 12834 and 23349.

Other changes

  • Preliminary support for defining the Cython language with a formal grammar. To try parsing your files against this grammar, use the --formal_grammar directive. Experimental.
  • _ is no longer considered a cacheable builtin as it could interfere with gettext.
  • Cythonize-computed metadata now cached in the generated C files.
  • Several corrections and extensions in numpy, cpython, and libcpp pxd files.

0.21.2 (2014-12-27)

Bugs fixed

  • Crash when assigning a C value to both a Python and C target at the same time.
  • Automatic coercion from C++ strings to str generated incomplete code that failed to compile.
  • Declaring a constructor in a C++ child class erroneously required a default constructor declaration in the super class.
  • resize_smart() in cpython.array was broken.
  • Functions in libcpp.cast are now declared as nogil.
  • Some missing C-API declarations were added.
  • Py3 main code in embedding program code was lacking casts.
  • Exception related to distutils "Distribution" class type in pyximport under latest CPython 2.7 and 3.4 releases when setuptools is being imported later.

0.21.1 (2014-10-18)

Features added

  • New cythonize option -a to generate the annotated HTML source view.
  • Missing C-API declarations in cpython.unicode were added.
  • Passing language='c++' into cythonize() globally enables C++ mode for all modules that were not passed as Extension objects (i.e. only source files and file patterns).
  • Py_hash_t is a known type (used in CPython for hash values).
  • PySlice_*() C-API functions are available from the cpython.slice module.
  • Allow arrays of C++ classes.

Bugs fixed

  • Reference leak for non-simple Python expressions in boolean and/or expressions.
  • To fix a name collision and to reflect availability on host platforms, standard C declarations [ clock(), time(), struct tm and tm* functions ] were moved from posix/time.pxd to a new libc/time.pxd. Patch by Charles Blake.
  • Rerunning unmodified modules in IPython's cython support failed. Patch by Matthias Bussonier.
  • Casting C++ std::string to Python byte strings failed when auto-decoding was enabled.
  • Fatal exceptions in global module init code could lead to crashes if the already created module was used later on (e.g. through a stale reference in sys.modules or elsewhere).
  • cythonize.py script was not installed on MS-Windows.

Other changes

  • Compilation no longer fails hard when unknown compilation options are passed. Instead, it raises a warning and ignores them (as it did silently before 0.21). This will be changed back to an error in a future release.

0.21 (2014-09-10)

Features added

  • C (cdef) functions allow inner Python functions.
  • Enums can now be declared as cpdef to export their values to the module's Python namespace. Cpdef enums in pxd files export their values to their own module, iff it exists.
  • Allow @staticmethod decorator to declare static cdef methods. This is especially useful for declaring "constructors" for cdef classes that can take non-Python arguments.
  • Taking a char* from a temporary Python string object is safer in more cases and can be done inside of non-trivial expressions, including arguments of a function call. A compile time error is raised only when such a pointer is assigned to a variable and would thus exceed the lifetime of the string itself.
  • Generators have new properties __name__ and __qualname__ that provide the plain/qualified name of the generator function (following CPython 3.5). See https://bugs.python.org/issue21205
  • The inline function modifier is available as a decorator @cython.inline in pure mode.
  • When cygdb is run in a virtualenv, it enables the same virtualenv inside of the debugger. Patch by Marc Abramowitz.
  • PEP 465: dedicated infix operator for matrix multiplication (A @ B).
  • HTML output of annotated code uses Pygments for code highlighting and generally received a major overhaul by Matthias Bussonier.
  • IPython magic support is now available directly from Cython with the command "%load_ext cython". Cython code can directly be executed in a cell when marked with "%%cython". Code analysis is available with "%%cython -a". Patch by Martín Gaitán.
  • Simple support for declaring Python object types in Python signature annotations. Currently requires setting the compiler directive annotation_typing=True.
  • New directive use_switch (defaults to True) to optionally disable the optimization of chained if statement to C switch statements.
  • Defines dynamic_cast et al. in libcpp.cast and C++ heap data structure operations in libcpp.algorithm.
  • Shipped header declarations in posix.* were extended to cover more of the POSIX API. Patches by Lars Buitinck and Mark Peek.

Optimizations

  • Simple calls to C implemented Python functions/methods are faster. This also speeds up many operations on builtins that Cython cannot otherwise optimise.
  • The "and"/"or" operators try to avoid unnecessary coercions of their arguments. They now evaluate the truth value of each argument independently and only coerce the final result of the whole expression to the target type (e.g. the type on the left side of an assignment). This also avoids reference counting overhead for Python values during evaluation and generally improves the code flow in the generated C code.
  • The Python expression "2 ** N" is optimised into bit shifting. See https://bugs.python.org/issue21420
  • Cascaded assignments (a = b = ...) try to minimise the number of type coercions.
  • Calls to slice() are translated to a straight C-API call.

Bugs fixed

  • Crash when assigning memory views from ternary conditional expressions.
  • Nested C++ templates could lead to unseparated ">>" characters being generated into the C++ declarations, which older C++ compilers could not parse.
  • Sending SIGINT (Ctrl-C) during parallel cythonize() builds could hang the child processes.
  • No longer ignore local setup.cfg files for distutils in pyximport. Patch by Martin Teichmann.
  • Taking a char* from an indexed Python string generated unsafe reference counting code.
  • Set literals now create all of their items before trying to add them to the set, following the behaviour in CPython. This makes a difference in the rare case that the item creation has side effects and some items are not hashable (or if hashing them has side effects, too).
  • Cython no longer generates the cross product of C functions for code that uses memory views of fused types in function signatures (e.g. cdef func(floating[:] a, floating[:] b)). This is considered the expected behaviour by most users and was previously inconsistent with other structured types like C arrays. Code that really wants all type combinations can create the same fused memoryview type under different names and use those in the signature to make it clear which types are independent.
  • Names that were unknown at compile time were looked up as builtins at runtime but not as global module names. Trying both lookups helps with globals() manipulation.
  • Fixed stl container conversion for typedef element types.
  • obj.pop(x) truncated large C integer values of x to Py_ssize_t.
  • __init__.pyc is recognised as marking a package directory (in addition to .py, .pyx and .pxd).
  • Syntax highlighting in cython-mode.el for Emacs no longer incorrectly highlights keywords found as part of longer names.
  • Correctly handle from cython.submodule cimport name.
  • Fix infinite recursion when using super with cpdef methods.
  • No-args dir() was not guaranteed to return a sorted list.

Other changes

  • The header line in the generated C files no longer contains the timestamp but only the Cython version that wrote it. This was changed to make builds more reproducible.
  • Removed support for CPython 2.4, 2.5 and 3.1.
  • The licensing implications on the generated code were clarified to avoid legal constraints for users.

0.20.2 (2014-06-16)

Features added

  • Some optimisations for set/frozenset instantiation.
  • Support for C++ unordered_set and unordered_map.

Bugs fixed

  • Access to attributes of optimised builtin methods (e.g. [].append.__name__) could fail to compile.
  • Memory leak when extension subtypes add a memory view as attribute to those of the parent type without having Python object attributes or a user provided dealloc method.
  • Compiler crash on readonly properties in "binding" mode.
  • Auto-encoding with c_string_encoding=ascii failed in Py3.3.
  • Crash when subtyping freelist enabled Cython extension types with Python classes that use __slots__.
  • Freelist usage is restricted to CPython to avoid problems with other Python implementations.
  • Memory leak in memory views when copying overlapping, contiguous slices.
  • Format checking when requesting non-contiguous buffers from cython.array objects was accidentally omitted in Py3.
  • C++ destructor calls in extension types could fail to compile in clang.
  • Buffer format validation failed for sequences of strings in structs.
  • Docstrings on extension type attributes in .pxd files were rejected.

0.20.1 (2014-02-11)

Bugs fixed

  • Build error under recent MacOS-X versions where isspace() could not be resolved by clang.
  • List/Tuple literals multiplied by more than one factor were only multiplied by the last factor instead of all.
  • Lookups of special methods (specifically for context managers) could fail in Python <= 2.6/3.1.
  • Local variables were erroneously appended to the signature introspection of Cython implemented functions with keyword-only arguments under Python 3.
  • In-place assignments to variables with inferred Python builtin/extension types could fail with type errors if the result value type was incompatible with the type of the previous value.
  • The C code generation order of cdef classes, closures, helper code, etc. was not deterministic, thus leading to high code churn.
  • Type inference could fail to deduce C enum types.
  • Type inference could deduce unsafe or inefficient types from integer assignments within a mix of inferred Python variables and integer variables.

0.20 (2014-01-18)

Features added

  • Support for CPython 3.4.
  • Support for calling C++ template functions.
  • yield is supported in finally clauses.
  • The C code generated for finally blocks is duplicated for each exit case to allow for better optimisations by the C compiler.
  • Cython tries to undo the Python optimisationism of assigning a bound method to a local variable when it can generate better code for the direct call.
  • Constant Python float values are cached.
  • String equality comparisons can use faster type specific code in more cases than before.
  • String/Unicode formatting using the '%' operator uses a faster C-API call.
  • bytearray has become a known type and supports coercion from and to C strings. Indexing, slicing and decoding is optimised. Note that this may have an impact on existing code due to type inference.
  • Using cdef basestring stringvar and function arguments typed as basestring is now meaningful and allows assigning exactly str and unicode objects, but no subtypes of these types.
  • Support for the __debug__ builtin.
  • Assertions in Cython compiled modules are disabled if the running Python interpreter was started with the "-O" option.
  • Some types that Cython provides internally, such as functions and generators, are now shared across modules if more than one Cython implemented module is imported.
  • The type inference algorithm works more fine granular by taking the results of the control flow analysis into account.
  • A new script in bin/cythonize provides a command line frontend to the cythonize() compilation function (including distutils build).
  • The new extension type decorator @cython.no_gc_clear prevents objects from being cleared during cyclic garbage collection, thus making sure that object attributes are kept alive until deallocation.
  • During cyclic garbage collection, attributes of extension types that cannot create reference cycles due to their type (e.g. strings) are no longer considered for traversal or clearing. This can reduce the processing overhead when searching for or cleaning up reference cycles.
  • Package compilation (i.e. __init__.py files) now works, starting with Python 3.3.
  • The cython-mode.el script for Emacs was updated. Patch by Ivan Andrus.
  • An option common_utility_include_dir was added to cythonize() to save oft-used utility code once in a separate directory rather than as part of each generated file.
  • unraisable_tracebacks directive added to control printing of tracebacks of unraisable exceptions.

Bugs fixed

  • Abstract Python classes that subtyped a Cython extension type failed to raise an exception on instantiation, and thus ended up being instantiated.
  • set.add(a_tuple) and set.discard(a_tuple) failed with a TypeError in Py2.4.
  • The PEP 3155 __qualname__ was incorrect for nested classes and inner classes/functions declared as global.
  • Several corner cases in the try-finally statement were fixed.
  • The metaclass of a Python class was not inherited from its parent class(es). It is now extracted from the list of base classes if not provided explicitly using the Py3 metaclass keyword argument. In Py2 compilation mode, a __metaclass__ entry in the class dict will still take precedence if not using Py3 metaclass syntax, but only after creating the class dict (which may have been done by a metaclass of a base class, see PEP 3115). It is generally recommended to use the explicit Py3 syntax to define metaclasses for Python types at compile time.
  • The automatic C switch statement generation behaves more safely for heterogeneous value types (e.g. mixing enum and char), allowing for a slightly wider application and reducing corner cases. It now always generates a 'default' clause to avoid C compiler warnings about unmatched enum values.
  • Fixed a bug where class hierarchies declared out-of-order could result in broken generated code.
  • Fixed a bug which prevented overriding const methods of C++ classes.
  • Fixed a crash when converting Python objects to C++ strings fails.

Other changes

  • In Py3 compilation mode, Python2-style metaclasses declared by a __metaclass__ class dict entry are ignored.
  • In Py3.4+, the Cython generator type uses tp_finalize() for safer cleanup instead of tp_del().

0.19.2 (2013-10-13)

Features added

Bugs fixed

  • Some standard declarations were fixed or updated, including the previously incorrect declaration of PyBuffer_FillInfo() and some missing bits in libc.math.
  • Heap allocated subtypes of type used the wrong base type struct at the C level.
  • Calling the unbound method dict.keys/value/items() in dict subtypes could call the bound object method instead of the unbound supertype method.
  • "yield" wasn't supported in "return" value expressions.
  • Using the "bint" type in memory views lead to unexpected results. It is now an error.
  • Assignments to global/closure variables could catch them in an illegal state while deallocating the old value.

Other changes

0.19.1 (2013-05-11)

Features added

  • Completely empty C-API structs for extension type slots (protocols like number/mapping/sequence) are no longer generated into the C code.
  • Docstrings that directly follow a public/readonly attribute declaration in a cdef class will be used as docstring of the auto-generated property. This fixes ticket 206.
  • The automatic signature documentation tries to preserve more semantics of default arguments and argument types. Specifically, bint arguments now appear as type bool.
  • A warning is emitted when negative literal indices are found inside of a code section that disables wraparound handling. This helps with fixing invalid code that might fail in the face of future compiler optimisations.
  • Constant folding for boolean expressions (and/or) was improved.
  • Added a build_dir option to cythonize() which allows one to place the generated .c files outside the source tree.

Bugs fixed

  • isinstance(X, type) failed to get optimised into a call to PyType_Check(), as done for other builtin types.
  • A spurious from datetime cimport * was removed from the "cpython" declaration package. This means that the "datetime" declarations (added in 0.19) are no longer available directly from the "cpython" namespace, but only from "cpython.datetime". This is the correct way of doing it because the declarations refer to a standard library module, not the core CPython C-API itself.
  • The C code for extension types is now generated in topological order instead of source code order to avoid C compiler errors about missing declarations for subtypes that are defined before their parent.
  • The memoryview type name no longer shows up in the module dict of modules that use memory views. This fixes trac ticket 775.
  • Regression in 0.19 that rejected valid C expressions from being used in C array size declarations.
  • In C++ mode, the C99-only keyword restrict could accidentally be seen by the GNU C++ compiler. It is now specially handled for both GCC and MSVC.
  • Testing large (> int) C integer values for their truth value could fail due to integer wrap-around.

Other changes

0.19 (2013-04-19)

Features added

  • New directives c_string_type and c_string_encoding to more easily and automatically convert between C strings and the different Python string types.
  • The extension type flag Py_TPFLAGS_HAVE_VERSION_TAG is enabled by default on extension types and can be disabled using the type_version_tag compiler directive.
  • EXPERIMENTAL support for simple Cython code level line tracing. Enabled by the "linetrace" compiler directive.
  • Cython implemented functions make their argument and return type annotations available through the __annotations__ attribute (PEP 3107).
  • Access to non-cdef module globals and Python object attributes is faster.
  • Py_UNICODE* coerces from and to Python unicode strings. This is helpful when talking to Windows APIs, which use compatible wchar_t arrays for strings. Note that the Py_UNICODE type is otherwise deprecated as of CPython 3.3.
  • isinstance(obj, basestring) is optimised. In Python 3 it only tests for instances of str (i.e. Py2 unicode).
  • The basestring builtin is mapped to str (i.e. Py2 unicode) when compiling the generated C code under Python 3.
  • Closures use freelists, which can speed up their creation quite substantially. This is also visible for short running generator expressions, for example.
  • A new class decorator @cython.freelist(N) creates a static freelist of N instances for an extension type, thus avoiding the costly allocation step if possible. This can speed up object instantiation by 20-30% in suitable scenarios. Note that freelists are currently only supported for base types, not for types that inherit from others.
  • Fast extension type instantiation using the Type.__new__(Type) idiom has gained support for passing arguments. It is also a bit faster for types defined inside of the module.
  • The Python2-only dict methods .iter*() and .view*() (requires Python 2.7) are automatically mapped to the equivalent keys/values/items methods in Python 3 for typed dictionaries.
  • Slicing unicode strings, lists and tuples is faster.
  • list.append() is faster on average.
  • raise Exception() from None suppresses the exception context in Py3.3.
  • Py3 compatible exec(tuple) syntax is supported in Py2 code.
  • Keyword arguments are supported for cdef functions.
  • External C++ classes can be declared nogil. Patch by John Stumpo. This fixes trac ticket 805.

Bugs fixed

  • 2-value slicing of unknown objects passes the correct slice when the getitem protocol is used instead of the getslice protocol (especially in Python 3), i.e. None values for missing bounds instead of [0,maxsize]. It is also a bit faster in some cases, e.g. for constant bounds. This fixes trac ticket 636.
  • Cascaded assignments of None values to extension type variables failed with a TypeError at runtime.
  • The __defaults__ attribute was not writable for Cython implemented functions.
  • Default values of keyword-only arguments showed up in __defaults__ instead of __kwdefaults__ (which was not implemented). Both are available for Cython implemented functions now, as specified in Python 3.x.
  • yield works inside of with gil sections. It previously lead to a crash. This fixes trac ticket 803.
  • Static methods without explicitly named positional arguments (e.g. having only *args) crashed when being called. This fixes trac ticket 804.
  • dir() without arguments previously returned an unsorted list, which now gets sorted as expected.
  • dict.items(), dict.keys() and dict.values() no longer return lists in Python 3.
  • Exiting from an except-as clause now deletes the exception in Python 3 mode.
  • The declarations of frexp() and ldexp() in math.pxd were incorrect.

Other changes

0.18 (2013-01-28)

Features added

  • Named Unicode escapes ("N{...}") are supported.
  • Python functions/classes provide the special attribute "__qualname__" as defined by PEP 3155.
  • Added a directive overflowcheck which raises an OverflowException when arithmetic with C ints overflow. This has a modest performance penalty, but is much faster than using Python ints.
  • Calls to nested Python functions are resolved at compile time.
  • Type inference works across nested functions.
  • py_bytes_string.decode(...) is optimised.
  • C const declarations are supported in the language.

Bugs fixed

  • Automatic C++ exception mapping didn't work in nogil functions (only in "with nogil" blocks).

Other changes

0.17.4 (2013-01-03)

Bugs fixed

  • Garbage collection triggered during deallocation of container classes could lead to a double-deallocation.

0.17.3 (2012-12-14)

Features added

Bugs fixed

  • During final interpreter cleanup (with types cleanup enabled at compile time), extension types that inherit from base types over more than one level that were cimported from other modules could lead to a crash.
  • Weak-reference support in extension types (with a cdef __weakref__ attribute) generated incorrect deallocation code.
  • In CPython 3.3, converting a Unicode character to the Py_UNICODE type could fail to raise an overflow for non-BMP characters that do not fit into a wchar_t on the current platform.
  • Negative C integer constants lost their longness suffix in the generated C code.

Other changes

0.17.2 (2012-11-20)

Features added

  • cythonize() gained a best effort compile mode that can be used to simply ignore .py files that fail to compile.

Bugs fixed

  • Replacing an object reference with the value of one of its cdef attributes could generate incorrect C code that accessed the object after deleting its last reference.
  • C-to-Python type coercions during cascaded comparisons could generate invalid C code, specifically when using the 'in' operator.
  • "obj[1,]" passed a single integer into the item getter instead of a tuple.
  • Cyclic imports at module init time did not work in Py3.
  • The names of C++ destructors for template classes were built incorrectly.
  • In pure mode, type casts in Cython syntax and the C ampersand operator are now rejected. Use the pure mode replacements instead.
  • In pure mode, C type names and the sizeof() function are no longer recognised as such and can be used as normal Python names.
  • The extended C level support for the CPython array type was declared too late to be used by user defined classes.
  • C++ class nesting was broken.
  • Better checking for required nullary constructors for stack-allocated C++ instances.
  • Remove module docstring in no-docstring mode.
  • Fix specialization for varargs function signatures.
  • Fix several compiler crashes.

Other changes

  • An experimental distutils script for compiling the CPython standard library was added as Tools/cystdlib.py.

0.17.1 (2012-09-26)

Features added

Bugs fixed

  • A reference leak was fixed in the new dict iteration code when the loop target was not a plain variable but an unpacked tuple.
  • Memory views did not handle the special case of a NULL buffer strides value, as allowed by PEP3118.

Other changes

0.17 (2012-09-01)

Features added

  • Alpha quality support for compiling and running Cython generated extension modules in PyPy (through cpyext). Note that this requires at least PyPy 1.9 and in many cases also adaptations in user code, especially to avoid borrowed references when no owned reference is being held directly in C space (a reference in a Python list or dict is not enough, for example). See the documentation on porting Cython code to PyPy.
  • "yield from" is supported (PEP 380) and a couple of minor problems with generators were fixed.
  • C++ STL container classes automatically coerce from and to the equivalent Python container types on typed assignments and casts. Note that the data in the containers is copied during this conversion.
  • C++ iterators can now be iterated over using "for x in cpp_container" whenever cpp_container has begin() and end() methods returning objects satisfying the iterator pattern (that is, it can be incremented, dereferenced, and compared (for non-equality)).
  • cdef classes can now have C++ class members (provided a zero-argument constructor exists)
  • A new cpython.array standard cimport file allows to efficiently talk to the stdlib array.array data type in Python 2. Since CPython does not export an official C-API for this module, it receives special casing by the compiler in order to avoid setup overhead on user side. In Python 3, both buffers and memory views on the array type already worked out of the box with earlier versions of Cython due to the native support for the buffer interface in the Py3 array module.
  • Fast dict iteration is now enabled optimistically also for untyped variables when the common iteration methods are used.
  • The unicode string processing code was adapted for the upcoming CPython 3.3 (PEP 393, new Unicode buffer layout).
  • Buffer arguments and memory view arguments in Python functions can be declared "not None" to raise a TypeError on None input.
  • c(p)def functions in pure mode can specify their return type with "@cython.returns()".
  • Automatic dispatch for fused functions with memoryview arguments
  • Support newaxis indexing for memoryviews
  • Support decorators for fused functions

Bugs fixed

  • Old-style Py2 imports did not work reliably in Python 3.x and were broken in Python 3.3. Regardless of this fix, it's generally best to be explicit about relative and global imports in Cython code because old-style imports have a higher overhead. To this end, "from __future__ import absolute_import" is supported in Python/Cython 2.x code now (previous versions of Cython already used it when compiling Python 3 code).
  • Stricter constraints on the "inline" and "final" modifiers. If your code does not compile due to this change, chances are these modifiers were previously being ignored by the compiler and can be removed without any performance regression.
  • Exceptions are always instantiated while raising them (as in Python), instead of risking to instantiate them in potentially unsafe situations when they need to be handled or otherwise processed.
  • locals() properly ignores names that do not have Python compatible types (including automatically inferred types).
  • Some garbage collection issues of memory views were fixed.
  • numpy.pxd compiles in Python 3 mode.
  • Several C compiler warnings were fixed.
  • Several bugs related to memoryviews and fused types were fixed.
  • Several bug-fixes and improvements related to cythonize(), including ccache-style caching.

Other changes

  • libc.string provides a convenience declaration for const uchar in addition to const char.
  • User declared char* types are now recognised as such and auto-coerce to and from Python bytes strings.
  • callable() and next() compile to more efficient C code.
  • list.append() is faster on average.
  • Modules generated by @cython.inline() are written into the directory pointed to by the environment variable CYTHON_CACHE_DIR if set.

0.16 (2012-04-21)

Features added

  • Enhancements to Cython's function type (support for weak references, default arguments, code objects, dynamic attributes, classmethods, staticmethods, and more)
  • Fused Types - Template-like support for functions and methods CEP 522 (docs)
  • Typed views on memory - Support for efficient direct and indirect buffers (indexing, slicing, transposing, ...) CEP 517 (docs)
  • super() without arguments
  • Final cdef methods (which translate into direct calls on known instances)

Bugs fixed

  • fix alignment handling for record types in buffer support

Other changes

  • support default arguments for closures
  • search sys.path for pxd files
  • support C++ template casting
  • faster traceback building and faster generator termination
  • support inplace operators on indexed buffers
  • allow nested prange sections

0.15.1 (2011-09-19)

Features added

Bugs fixed

Other changes

0.15 (2011-08-05)

Features added

  • Generators (yield) - Cython has full support for generators, generator expressions and PEP 342 coroutines.
  • The nonlocal keyword is supported.
  • Re-acquiring the gil: with gil - works as expected within a nogil context.
  • OpenMP support: prange.
  • Control flow analysis prunes dead code and emits warnings and errors about uninitialised variables.
  • Debugger command cy set to assign values of expressions to Cython variables and cy exec counterpart $cy_eval().
  • Exception chaining PEP 3134.
  • Relative imports PEP 328.
  • Improved pure syntax including cython.cclass, cython.cfunc, and cython.ccall.
  • The with statement has its own dedicated and faster C implementation.
  • Support for del.
  • Boundschecking directives implemented for builtin Python sequence types.
  • Several updates and additions to the shipped standard library .pxd files.
  • Forward declaration of types is no longer required for circular references.

Bugs fixed

Other changes

  • Uninitialized variables are no longer initialized to None and accessing them has the same semantics as standard Python.
  • globals() now returns a read-only dict of the Cython module's globals, rather than the globals of the first non-Cython module in the stack
  • Many C++ exceptions are now special cased to give closer Python counterparts. This means that except+ functions that formerly raised generic RuntimeErrors may raise something else such as ArithmeticError.
  • The inlined generator expressions (introduced in Cython 0.13) were disabled in favour of full generator expression support. This breaks code that previously used them inside of cdef functions (usage in def functions continues to work) and induces a performance regression for cases that continue to work but that were previously inlined. We hope to reinstate this feature in the near future.

0.14.1 (2011-02-04)

Features added

  • The gdb debugging support was extended to include all major Cython features, including closures.
  • raise MemoryError() is now safe to use as Cython replaces it with the correct C-API call.

Bugs fixed

Other changes

  • Decorators on special methods of cdef classes now raise a compile time error rather than being ignored.
  • In Python 3 language level mode (-3 option), the 'str' type is now mapped to 'unicode', so that cdef str s declares a Unicode string even when running in Python 2.

0.14 (2010-12-14)

Features added

  • Python classes can now be nested and receive a proper closure at definition time.
  • Redefinition is supported for Python functions, even within the same scope.
  • Lambda expressions are supported in class bodies and at the module level.
  • Metaclasses are supported for Python classes, both in Python 2 and Python 3 syntax. The Python 3 syntax (using a keyword argument in the type declaration) is preferred and optimised at compile time.
  • "final" extension classes prevent inheritance in Python space. This feature is available through the new "cython.final" decorator. In the future, these classes may receive further optimisations.
  • "internal" extension classes do not show up in the module dictionary. This feature is available through the new "cython.internal" decorator.
  • Extension type inheritance from builtin types, such as "cdef class MyUnicode(unicode)", now works without further external type redeclarations (which are also strongly discouraged now and continue to issue a warning).
  • GDB support. https://docs.cython.org/src/userguide/debugging.html
  • A new build system with support for inline distutils directives, correct dependency tracking, and parallel compilation. https://github.com/cython/cython/wiki/enhancements-distutils_preprocessing
  • Support for dynamic compilation at runtime via the new cython.inline function and cython.compile decorator. https://github.com/cython/cython/wiki/enhancements-inline
  • "nogil" blocks are supported when compiling pure Python code by writing "with cython.nogil".
  • Iterating over arbitrary pointer types is now supported, as is an optimized version of the in operator, e.g. x in ptr[a:b].

Bugs fixed

  • In parallel assignments, the right side was evaluated in reverse order in 0.13. This could result in errors if it had side effects (e.g. function calls).
  • In some cases, methods of builtin types would raise a SystemError instead of an AttributeError when called on None.

Other changes

  • Constant tuples are now cached over the lifetime of an extension module, just like CPython does. Constant argument tuples of Python function calls are also cached.
  • Closures have tightened to include exactly the names used in the inner functions and classes. Previously, they held the complete locals of the defining function.
  • The builtin "next()" function in Python 2.6 and later is now implemented internally and therefore available in all Python versions. This makes it the preferred and portable way of manually advancing an iterator.
  • In addition to the previously supported inlined generator expressions in 0.13, "sorted(genexpr)" can now be used as well. Typing issues were fixed in "sum(genexpr)" that could lead to invalid C code being generated. Other known issues with inlined generator expressions were also fixed that make upgrading to 0.14 a strong recommendation for code that uses them. Note that general generators and generator expressions continue to be not supported.
  • Inplace arithmetic operators now respect the cdivision directive and are supported for complex types.
  • Typing a variable as type "complex" previously gave it the Python object type. It now uses the appropriate C/C++ double complex type. A side-effect is that assignments and typed function parameters now accept anything that Python can coerce to a complex, including integers and floats, and not only complex instances.
  • Large integer literals pass through the compiler in a safer way. To prevent truncation in C code, non 32-bit literals are turned into Python objects if not used in a C context. This context can either be given by a clear C literal suffix such as "UL" or "LL" (or "L" in Python 3 code), or it can be an assignment to a typed variable or a typed function argument, in which case it is up to the user to take care of a sufficiently large value space of the target.
  • Python functions are declared in the order they appear in the file, rather than all being created at module creation time. This is consistent with Python and needed to support, for example, conditional or repeated declarations of functions. In the face of circular imports this may cause code to break, so a new --disable-function-redefinition flag was added to revert to the old behavior. This flag will be removed in a future release, so should only be used as a stopgap until old code can be fixed.

0.13 (2010-08-25)

Features added

  • Closures are fully supported for Python functions. Cython supports inner functions and lambda expressions. Generators and generator expressions are not supported in this release.
  • Proper C++ support. Cython knows about C++ classes, templates and overloaded function signatures, so that Cython code can interact with them in a straight forward way.
  • Type inference is enabled by default for safe C types (e.g. double, bint, C++ classes) and known extension types. This reduces the need for explicit type declarations and can improve the performance of untyped code in some cases. There is also a verbose compile mode for testing the impact on user code.
  • Cython's for-in-loop can iterate over C arrays and sliced pointers. The type of the loop variable will be inferred automatically in this case.
  • The Py_UNICODE integer type for Unicode code points is fully supported, including for-loops and 'in' tests on unicode strings. It coerces from and to single character unicode strings. Note that untyped for-loop variables will automatically be inferred as Py_UNICODE when iterating over a unicode string. In most cases, this will be much more efficient than yielding sliced string objects, but can also have a negative performance impact when the variable is used in a Python context multiple times, so that it needs to coerce to a unicode string object more than once. If this happens, typing the loop variable as unicode or object will help.
  • The built-in functions any(), all(), sum(), list(), set() and dict() are inlined as plain for loops when called on generator expressions. Note that generator expressions are not generally supported apart from this feature. Also, tuple(genexpr) is not currently supported - use tuple([listcomp]) instead.
  • More shipped standard library declarations. The python* and stdlib/stdio .pxd files have been deprecated in favor of clib.* and cpython[.*] and may get removed in a future release.
  • Pure Python mode no longer disallows non-Python keywords like 'cdef', 'include' or 'cimport'. It also no longer recognises syntax extensions like the for-from loop.
  • Parsing has improved for Python 3 syntax in Python code, although not all features are correctly supported. The missing Python 3 features are being worked on for the next release.
  • from __future__ import print_function is supported in Python 2.6 and later. Note that there is currently no emulation for earlier Python versions, so code that uses print() with this future import will require at least Python 2.6.
  • New compiler directive language_level (valid values: 2 or 3) with corresponding command line options -2 and -3 requests source code compatibility with Python 2.x or Python 3.x respectively. Language level 3 currently enforces unicode literals for unprefixed string literals, enables the print function (requires Python 2.6 or later) and keeps loop variables in list comprehensions from leaking.
  • Loop variables in set/dict comprehensions no longer leak into the surrounding scope (following Python 2.7). List comprehensions are unchanged in language level 2.
  • print >> stream

Bugs fixed

Other changes

  • The availability of type inference by default means that Cython will also infer the type of pointers on assignments. Previously, code like this:

    cdef char* s = ...
untyped_variable = s

    would convert the char* to a Python bytes string and assign that. This is no longer the case and no coercion will happen in the example above. The correct way of doing this is through an explicit cast or by typing the target variable, i.e.

    cdef char* s = ...
untyped_variable1 = <bytes>s
untyped_variable2 = <object>s

cdef object py_object = s
cdef bytes  bytes_string = s
  • bool is no longer a valid type name by default. The problem is that it's not clear whether bool should refer to the Python type or the C++ type, and expecting one and finding the other has already led to several hard-to-find bugs. Both types are available for importing: you can use from cpython cimport bool for the Python bool type, and from libcpp cimport bool for the C++ type. bool is still a valid object by default, so one can still write bool(x).
  • __getsegcount__ is now correctly typed to take a Py_size_t* rather than an int*.

0.12.1 (2010-02-02)

Features added

  • Type inference improvements.
    • There have been several bug fixes and improvements to the type inferencer.
    • Notably, there is now a "safe" mode enabled by setting the infer_types directive to None. (The None here refers to the "default" mode, which will be the default in 0.13.) This safe mode limits inference to Python object types and C doubles, which should speed up execution without affecting any semantics such as integer overflow behavior like infer_types=True might. There is also an infer_types.verbose option which allows one to see what types are inferred.
  • The boundscheck directive works for lists and tuples as well as buffers.
  • len(s) and s.decode("encoding") are efficiently supported for char* s.
  • Cython's INLINE macro has been renamed to CYTHON_INLINE to reduce conflict and has better support for the MSVC compiler on Windows. It is no longer clobbered if externally defined.
  • Revision history is now omitted from the source package, resulting in a 85% size reduction. Running make repo will download the history and turn the directory into a complete Mercurial working repository.
  • Cython modules don't need to be recompiled when the size of an external type grows. (A warning, rather than an error, is produced.) This should be helpful for binary distributions relying on NumPy.

Bugs fixed

  • Several other bugs and minor improvements have been made. This release should be fully backwards compatible with 0.12.

Other changes

0.12 (2009-11-23)

Features added

  • Type inference with the infer_types directive
  • Seamless C++ complex support
  • Fast extension type instantiation using the normal Python meme obj = MyType.__new__(MyType)
  • Improved support for Py3.1
  • Cython now runs under Python 3.x using the 2to3 tool
  • unittest support for doctests in Cython modules
  • Optimised handling of C strings (char*): for c in cstring[2:50] and cstring.decode()
  • Looping over c pointers: for i in intptr[:50].
  • pyximport improvements
  • cython_freeze improvements

Bugs fixed

  • Many bug fixes

Other changes

  • Many other optimisation, e.g. enumerate() loops, parallel swap assignments (a,b = b,a), and unicode.encode()
  • More complete numpy.pxd

0.11.2 (2009-05-20)

Features added

  • There's now native complex floating point support! C99 complex will be used if complex.h is included, otherwise explicit complex arithmetic working on all C compilers is used. [Robert Bradshaw]

    cdef double complex a = 1 + 0.3j
cdef np.ndarray[np.complex128_t, ndim=2] arr = \
   np.zeros(10, np.complex128)
  • Cython can now generate a main()-method for embedding of the Python interpreter into an executable (see 289) [Robert Bradshaw]
  • @wraparound directive (another way to disable arr[idx] for negative idx) [Dag Sverre Seljebotn]
  • Correct support for NumPy record dtypes with different alignments, and "cdef packed struct" support [Dag Sverre Seljebotn]
  • @callspec directive, allowing custom calling convention macros [Lisandro Dalcin]

Bugs fixed

Other changes

  • Bug fixes and smaller improvements. For the full list, see [1].