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bpo-46655: allow stringized TypeAlias with get_type_hints #31156

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Merged
merged 3 commits into from
Feb 6, 2022
+7 −1
Merged

bpo-46655: allow stringized TypeAlias with get_type_hints #31156

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64f45a7
allow stringized TypeAlias with get_type_hints
GBeauregard Feb 6, 2022
7b425d9
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 6, 2022
2c36c6c
Merge branch 'python:main' into fix-typealias
GBeauregard Feb 6, 2022
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5 changes: 5 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4854,6 +4854,11 @@ def test_no_isinstance(self):
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)
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2 changes: 1 addition & 1 deletion Lib/typing.py
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Expand Up @@ -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")
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-02-06-08-54-03.bpo-46655.DiLzYv.rst
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@@ -0,0 +1 @@
In :func:`typing.get_type_hints`, support evaluating bare stringified ``TypeAlias`` annotations. Patch by Gregory Beauregard.