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isinstance can take typing.Union as second arg in 3.10 and newer #12137
Description
Currently it allows for types.UnionType but not typing.Union
if sys.version_info >= (3, 10):
_ClassInfo: TypeAlias = type | types.UnionType | tuple[_ClassInfo, ...]
else:
_ClassInfo: TypeAlias = type | tuple[_ClassInfo, ...]
def isinstance(obj: object, class_or_tuple: _ClassInfo, /) -> bool: ...
I think mypy currently assumes that whatever typeshed says for isinstance has no false positives
Activity
JelleZijlstra commentedon Jun 13, 2024
I'm not sure we could express this in typeshed.
Union[int, str]is not an instance oftyping.Union.AlexWaygood commentedon Jun 13, 2024
(I don't object to revisiting this, but this is a duplicate of #7505)
hauntsaninja commentedon Jun 13, 2024
Thanks, looks like most of the relevant discussion is on #7508. Sounds like most people are surprised that isinstance works at all with old Union / think that type checkers should special case this even more than they currently do