Non-overlapping identity check error for typing.get_origin

[eltoder]

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.

[JelleZijlstra]

We already have a series of overloads for different cases, and the type return is only for GenericAlias arguments:

typeshed/stdlib/typing.pyi

Line 812 in 7646d38

if sys.version_info >= (3, 10):

I think this might be better seen as a bug in mypy, or at least an unfortunate overload resolution.

[AlexWaygood]

or at least an unfortunate overload resolution.

My (untested) guess would be that because TypeSpec is an alias for Any, any of the get_origin overloads are a valid match for the code snippet above. So mypy just blindly picks the first overload, and infers that the object returned by the get_origin call is an instance of ParamSpec.

typeshed/stdlib/typing.pyi

Lines 813 to 814 in 7646d38

	@overload
	def get_origin(tp: ParamSpecArgs | ParamSpecKwargs) -> ParamSpec: ...

This is indeed slightly unfortunate, but I'm not sure what we can do about it.

[eltoder]

Alright, opened a mypy bug: python/mypy#15630

[AlexWaygood]

Going to close this, as I don't think there's anything actionable for typeshed here; this is a mypy bug