TypeIs and unions of Callable

[Viicos]

Code sample in pyright playground

from typing import Any, Callable, TypeIs


def is_single_callable(c: Callable[[], Any] | Callable[[int], Any]) -> TypeIs[Callable[[int], Any]]:
    ...


def test(c: Callable[[], Any] | Callable[[int], Any]):
    if is_single_callable(c):
        reveal_type(c)  # (int) -> Any
    else:
        reveal_type(c)  # (() -> Any) | ((int) -> Any)

I'm wondering if Pyright can safely narrow c to ((int) -> Any) in the else branch

[erictraut]

I think it would be type safe to narrow it further in the fall-through case. The question is whether such an enhancement is worthwhile. Pyright's current behavior is arguably correct, but the resulting type could be more precise (narrower). Mypy appears to over-narrow the type to Never in this case, which I would consider a bug.

[Viicos]

Yes I also noticed this in mypy, jus opened an issue.

The question is whether such an enhancement is worthwhile.

Honestly I can leave without it, implementing it might be a bit painful as callable signatures may overlap in some way. I mainly wanted to confirm this wasn't by design and could be safely narrowed. Thanks!