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bpo-46655: allow stringized TypeAlias with get_type_hints (GH-31156)

This commit is contained in:
Gregory Beauregard 2022-02-06 15:16:22 -08:00 committed by GitHub
parent 06b8f1615b
commit 77b025be4a
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 7 additions and 1 deletions
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5
Lib/test/test_typing.py
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@ -4866,6 +4866,11 @@ class TypeAliasTests(BaseTestCase):
with self.assertRaises(TypeError):
isinstance(42, TypeAlias)
def test_stringized_usage(self):
class A:
a: "TypeAlias"
self.assertEqual(get_type_hints(A), {'a': TypeAlias})
def test_no_issubclass(self):
with self.assertRaises(TypeError):
issubclass(Employee, TypeAlias)

2
Lib/typing.py
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@ -174,7 +174,7 @@ def _type_check(arg, msg, is_argument=True, module=None, *, allow_special_forms=
if (isinstance(arg, _GenericAlias) and
arg.__origin__ in invalid_generic_forms):
raise TypeError(f"{arg} is not valid as type argument")
if arg in (Any, NoReturn, ClassVar, Final):
if arg in (Any, NoReturn, ClassVar, Final, TypeAlias):
return arg
if isinstance(arg, _SpecialForm) or arg in (Generic, Protocol):
raise TypeError(f"Plain {arg} is not valid as type argument")

1
Misc/NEWS.d/next/Library/2022-02-06-08-54-03.bpo-46655.DiLzYv.rst Normal file
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@ -0,0 +1 @@
In :func:`typing.get_type_hints`, support evaluating bare stringified ``TypeAlias`` annotations. Patch by Gregory Beauregard.