Parametrization with Variables Unexpectedly Changes Fixture Scope from Class-Level to Function-Level

[yogendrasinghx]

I have a setup fixture that I've parameterized with class-level scope. When I directly specify the argument values as [("chrome", "windows", "latest")], it works fine, maintaining the class-level scope. However, when I try to use variables to set these argument values, I've noticed that the scope unexpectedly shifts to function-level.

tests/test_app.py

import pytest


@pytest.mark.usefixtures("setup")
class TestSmoke:
    def test_1(self):
        assert True

    def test_2(self):
        assert True

Scenario 1 with hardcoded values

tests/conftest.py

import pytest

def pytest_generate_tests(metafunc):
    if 'setup' in metafunc.fixturenames:
        metafunc.parametrize("setup",argvalues=[("chrome", "windows", "latest")], indirect=True, scope='class')


@pytest.fixture
def setup(request):
    print(f"\nSetting up")
    print(f"Param {request.param}")
    print(f"fixture (scope={request.scope})")

    yield
    print(f"\nTearing down")

Output

python -m pytest -s -v -k "TestSmoke" tests
======================================================================================================= test session starts =======================================================================================================
platform darwin -- Python 3.12.2, pytest-8.1.1, pluggy-1.4.0 -- /Volumes/T7/mywork/pythonProject/dynamic_parameter/venv/bin/python
cachedir: .pytest_cache
rootdir: /Volumes/T7/mywork/pythonProject/dynamic_parameter
collected 2 items                                                                                                                                                                                                                 

tests/test_app.py::TestSmoke::test_1[setup0] 
Setting up
Param ('chrome', 'windows', 'latest')
fixture (scope=class)
PASSED
tests/test_app.py::TestSmoke::test_2[setup0] PASSED
Tearing down

Scenario 2 with variable values

tests/conftest.py

import pytest


def pytest_generate_tests(metafunc):
    browser_name = "chrome"
    os_name = "windows"
    browser_version = "latest"

    if 'setup' in metafunc.fixturenames:
        metafunc.parametrize("setup", argvalues=[(os_name, browser_name, browser_version)], indirect=True, scope='class')


@pytest.fixture
def setup(request):
    print(f"\nSetting up")
    print(f"Param {request.param}")
    yield
    print(f"\nTearing down")

Output

python -m pytest -s -v -k "TestSmoke" tests
======================================================================================================= test session starts =======================================================================================================
platform darwin -- Python 3.12.2, pytest-7.4.4, pluggy-1.4.0 -- /Volumes/T7/mywork/pythonProject/dynamic_parameter/venv/bin/python
cachedir: .pytest_cache
rootdir: /Volumes/T7/mywork/pythonProject/dynamic_parameter
collected 2 items                                                                                                                                                                                                                 

tests/test_app.py::TestSmoke::test_1[setup0] 
Setting up
Param ('windows', 'chrome', 'latest')
PASSED
tests/test_app.py::TestSmoke::test_2[setup0] 
Tearing down

Setting up
Param ('windows', 'chrome', 'latest')
PASSED
Tearing down

(venv) yogen@Mac-mini dynamic_parameter % pip list
Package        Version
-------------- -------
attrs          23.2.0
iniconfig      2.0.0
more-itertools 10.2.0
packaging      24.0
pip            24.0
pluggy         1.4.0
py             1.11.0
pytest         8.1.1
toml           0.10.2
wcwidth        0.2.13

[The-Compiler]

Slightly simpler example:

import pytest


@pytest.mark.usefixtures("fixt")
class TestSmoke:
    def test_1(self):
        assert True

    def test_2(self):
        assert True

import pytest


def pytest_generate_tests(metafunc):
    if "fixt" in metafunc.fixturenames:
        arg = "latest"
        metafunc.parametrize(
            "fixt",
            argvalues=[
                (
                    arg,
                    # "latest",
                )
            ],
            indirect=True,
            scope="class",
        )


@pytest.fixture
def fixt(request):
    yield

with --setup-show:

tests/test_app.py 
        SETUP    F fixt[('latest',)]
        tests/test_app.py::TestSmoke::test_1[fixt0] (fixtures used: fixt, request).
        TEARDOWN F fixt[('latest',)]
        SETUP    F fixt[('latest',)]
        tests/test_app.py::TestSmoke::test_2[fixt0] (fixtures used: fixt, request).
        TEARDOWN F fixt[('latest',)]

but when commenting out arg, and using "latest", instead:

tests/test_app.py 
        SETUP    F fixt[('latest',)]
        tests/test_app.py::TestSmoke::test_1[fixt0] (fixtures used: fixt, request).
        tests/test_app.py::TestSmoke::test_2[fixt0] (fixtures used: fixt, request).
        TEARDOWN F fixt[('latest',)]

I'm... completely flabbergasted. How is this even possible‽

[RonnyPfannschmidt]

@The-Compiler i suspect/fear we somewhere match object identities

when the string is passed as a constant, its likely the python interpreter render it as single tuple value instead of creating it

if that suspicion holds true, then can expect the behaviour as you observe

[RonnyPfannschmidt]

i jsut made a small test in ipython on python 3.12

In [1]: import dis

In [2]: def fun():
   ...:     a = ""
   ...:     return (a,)
   ...: 

In [3]: print(dis.dis(fun))
  1           0 RESUME                   0

  2           2 LOAD_CONST               1 ('')
              4 STORE_FAST               0 (a)

  3           6 LOAD_FAST                0 (a)
              8 BUILD_TUPLE              1
             10 RETURN_VALUE
None

In [4]: def fun2():
   ...:     return ("",)
   ...: 

In [5]: print(dis.dis(fun2))
  1           0 RESUME                   0

  2           2 RETURN_CONST             1 (('',))
None

[RonnyPfannschmidt]

its possible #11257 fixes this