Remove the ABC from Distribution. Fixes #422.

importlib_metadata/__init__.py

@@ -31,7 +31,7 @@
 from importlib import import_module
 from importlib.abc import MetaPathFinder
 from itertools import starmap
-from typing import List, Mapping, Optional
+from typing import List, Mapping, Optional, cast
 
 
 __all__ = [
@@ -348,23 +348,22 @@ def __repr__(self):
         return f'<FileHash mode: {self.mode} value: {self.value}>'
 
 
-class Distribution(metaclass=abc.ABCMeta):
+class Distribution:
     """A Python distribution package."""
 
-    @abc.abstractmethod
-    def read_text(self, filename):
+    def read_text(self, filename) -> Optional[str]:
         """Attempt to load metadata file given by the name.
 
         :param filename: The name of the file in the distribution info.
         :return: The text if found, otherwise None.
         """
 
-    @abc.abstractmethod
     def locate_file(self, path):
         """
         Given a path to a file in this distribution, return a path
         to it.
         """
+        raise NotImplementedError
 
     @classmethod
     def from_name(cls, name: str):
@@ -426,14 +425,15 @@ def metadata(self) -> _meta.PackageMetadata:
         The returned object will have keys that name the various bits of
         metadata.  See PEP 566 for details.
         """
-        text = (
+        opt_text = (
             self.read_text('METADATA')
             or self.read_text('PKG-INFO')
             # This last clause is here to support old egg-info files.  Its
             # effect is to just end up using the PathDistribution's self._path
             # (which points to the egg-info file) attribute unchanged.
             or self.read_text('')
         )
+        text = cast(str, opt_text)
         return _adapters.Message(email.message_from_string(text))
 
     @property

tests/test_main.py

@@ -44,10 +44,6 @@ def test_package_not_found_mentions_metadata(self):
 
         assert "metadata" in str(ctx.exception)
 
-    def test_abc_enforced(self):
-        with self.assertRaises(TypeError):
-            type('DistributionSubclass', (Distribution,), {})()
-
     @fixtures.parameterize(
         dict(name=None),
         dict(name=''),