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[3.8] bpo-40398: Fix typing.get_args() for special generic aliases. (GH-19720) #19857

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Merged
merged 1 commit into from
May 2, 2020
Merged

[3.8] bpo-40398: Fix typing.get_args() for special generic aliases. (GH-19720) #19857

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9 changes: 8 additions & 1 deletion Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2913,6 +2913,9 @@ class C(Generic[T]): pass
self.assertIs(get_origin(Generic), Generic)
self.assertIs(get_origin(Generic[T]), Generic)
self.assertIs(get_origin(List[Tuple[T, T]][int]), list)
self.assertIs(get_origin(List), list)
self.assertIs(get_origin(Tuple), tuple)
self.assertIs(get_origin(Callable), collections.abc.Callable)

def test_get_args(self):
T = TypeVar('T')
Expand All @@ -2928,11 +2931,15 @@ class C(Generic[T]): pass
(int, Tuple[str, int]))
self.assertEqual(get_args(typing.Dict[int, Tuple[T, T]][Optional[int]]),
(int, Tuple[Optional[int], Optional[int]]))
self.assertEqual(get_args(Callable[[], T][int]), ([], int,))
self.assertEqual(get_args(Callable[[], T][int]), ([], int))
self.assertEqual(get_args(Callable[..., int]), (..., int))
self.assertEqual(get_args(Union[int, Callable[[Tuple[T, ...]], str]]),
(int, Callable[[Tuple[T, ...]], str]))
self.assertEqual(get_args(Tuple[int, ...]), (int, ...))
self.assertEqual(get_args(Tuple[()]), ((),))
self.assertEqual(get_args(List), ())
self.assertEqual(get_args(Tuple), ())
self.assertEqual(get_args(Callable), ())


class CollectionsAbcTests(BaseTestCase):
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2 changes: 1 addition & 1 deletion Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1300,7 +1300,7 @@ def get_args(tp):
get_args(Union[int, Tuple[T, int]][str]) == (int, Tuple[str, int])
get_args(Callable[[], T][int]) == ([], int)
"""
if isinstance(tp, _GenericAlias):
if isinstance(tp, _GenericAlias) and not tp._special:
res = tp.__args__
if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
res = (list(res[:-1]), res[-1])
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2020-04-26-22-25-36.bpo-40398.OdXnR3.rst
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@@ -0,0 +1,2 @@
:func:`typing.get_args` now always returns an empty tuple for special
generic aliases.