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Non-overlapping identity check error for typing.get_origin #10405
Description
The following example produces an error in mypy --strict mode:
import typing
TypeSpec = typing.Any
def is_union(spec: TypeSpec) -> bool:
return typing.get_origin(spec) is typing.Union(it does work without the type alias).
This gives:
$ mypy --strict t.py
t.py:6: error: Non-overlapping identity check (left operand type: "type", right operand type: "<typing special form>") [comparison-overlap]
It looks like get_origin() is declared to return type, but it can actually return some other things, notably Union and Literal.
mypy versions 1.4.1.
Activity
JelleZijlstra commentedon Jul 5, 2023
We already have a series of overloads for different cases, and the
typereturn is only forGenericAliasarguments:typeshed/stdlib/typing.pyi
Line 812 in 7646d38
I think this might be better seen as a bug in mypy, or at least an unfortunate overload resolution.
AlexWaygood commentedon Jul 8, 2023
My (untested) guess would be that because
TypeSpecis an alias forAny, any of theget_originoverloads are a valid match for the code snippet above. So mypy just blindly picks the first overload, and infers that the object returned by theget_origincall is an instance ofParamSpec.typeshed/stdlib/typing.pyi
Lines 813 to 814 in 7646d38
This is indeed slightly unfortunate, but I'm not sure what we can do about it.
eltoder commentedon Jul 9, 2023
Alright, opened a mypy bug: python/mypy#15630
AlexWaygood commentedon Jul 22, 2023
Going to close this, as I don't think there's anything actionable for typeshed here; this is a mypy bug