"Callable | Callable" not callable [misc]

[jolaf]

The following code:

from collections.abc import Callable, Sequence
from functools import partial, reduce
from typing import cast, Any

CA = Callable[[Any], Any]
CB = Callable[[Callable[..., Any], Any], Any]

def f(s: Sequence[CA | CB]) -> CA:
    return cast(CA, reduce(lambda a, b: partial(b, a), s))

produces the following output:

test.py: note: In function "f":
test.py:9:41: error: "Callable[[Any], Any] | Callable[[Callable[..., Any], Any], Any]" not callable  [misc]
        return cast(CA, reduce(lambda a, b: partial(b, a), s))
                                            ^

This looks like a false positive to me.

$ mypy --version
mypy 1.11.1 (compiled: yes)

$ python --version
Python 3.12.3

$ lsb_release -d
No LSB modules are available.
Description:	Ubuntu 24.04 LTS

[hauntsaninja]

This is the same as many other issues, where mypy computes join between callables to builtins.function. In this case join of [def (Any) -> Any and def (def (*Any, **Any) -> Any, Any) -> Any]. Happens to shows up in 1.11 because we now type check functools.partial more closely, but underlying issue is old. Seems tricky to turn the callsite in extract_callable_type to return a union

[bswck]

I've taken on the challenge of fixing this. It's my first time working with mypy, so bear with me or let me know if someone else fixes it.

[jolaf]

I've taken on the challenge of fixing this. It's my first time working with mypy, so bear with me or let me know if someone else fixes it.

Thanks!!

[hauntsaninja]

This was fixed in #17903