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| author | Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> | 2021-08-28 18:09:45 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2021-08-28 18:09:45 (GMT) |
| commit | 81fa08c5ea2cf15254b951034b9d6c7358f96d79 (patch) | |
| tree | fc4d745be06f471fda1ccdf71555a4fe19077f23 | |
| parent | cd986e903176d28ed795f65ba14e6fcbf2a65e3d (diff) | |
| download | cpython-81fa08c5ea2cf15254b951034b9d6c7358f96d79.zip cpython-81fa08c5ea2cf15254b951034b9d6c7358f96d79.tar.gz cpython-81fa08c5ea2cf15254b951034b9d6c7358f96d79.tar.bz2 | |
bpo-44524: Fix cryptic TypeError message when trying to subclass special forms in `typing` (GH-27710)
This was a Python 3.9 regression.
(cherry picked from commit a3a4d20d6798aa2975428d51f3a4f890248810cb)
Co-authored-by: Yurii Karabas <1998uriyyo@gmail.com>
| -rw-r--r-- | Lib/test/test_typing.py | 16 | ||||
| -rw-r--r-- | Lib/typing.py | 3 | ||||
| -rw-r--r-- | Misc/NEWS.d/next/Library/2021-08-10-16-57-10.bpo-44524.dk9QX4.rst | 2 |
3 files changed, 21 insertions, 0 deletions
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py index 7b2fd69..459af25 100644 --- a/Lib/test/test_typing.py +++ b/Lib/test/test_typing.py @@ -2418,6 +2418,22 @@ class GenericTests(BaseTestCase): self.assertEqual(c.from_b, 'b') self.assertEqual(c.from_c, 'c') + def test_subclass_special_form(self): + for obj in ( + ClassVar[int], + Final[int], + Union[int, float], + Optional[int], + Literal[1, 2], + Concatenate[int, ParamSpec("P")], + TypeGuard[int], + ): + with self.subTest(msg=obj): + with self.assertRaisesRegex( + TypeError, f'^{re.escape(f"Cannot subclass {obj!r}")}$' + ): + class Foo(obj): + pass class ClassVarTests(BaseTestCase): diff --git a/Lib/typing.py b/Lib/typing.py index 423329a..4c2d9fc 100644 --- a/Lib/typing.py +++ b/Lib/typing.py @@ -1081,6 +1081,9 @@ class _GenericAlias(_BaseGenericAlias, _root=True): return operator.getitem, (origin, args) def __mro_entries__(self, bases): + if isinstance(self.__origin__, _SpecialForm): + raise TypeError(f"Cannot subclass {self!r}") + if self._name: # generic version of an ABC or built-in class return super().__mro_entries__(bases) if self.__origin__ is Generic: diff --git a/Misc/NEWS.d/next/Library/2021-08-10-16-57-10.bpo-44524.dk9QX4.rst b/Misc/NEWS.d/next/Library/2021-08-10-16-57-10.bpo-44524.dk9QX4.rst new file mode 100644 index 0000000..bc3659f --- /dev/null +++ b/Misc/NEWS.d/next/Library/2021-08-10-16-57-10.bpo-44524.dk9QX4.rst @@ -0,0 +1,2 @@ +Make exception message more useful when subclass from typing special form +alias. Patch provided by Yurii Karabas. |