Question: Partial callable signature

[mehdigmira]

Hello,

When using decorators, we often know that the function that will be decorated should take param x and y, but we don't care about the rest of the parameters. Is there currently a way to do this ?
Something like Callable[[str,...], Any] would be perfect. It would work for f(x: str) but also for f(x: str, y: int) and f(x: str, *args, **kwargs)

[JelleZijlstra]

You can do this with callable protocols (https://mypy.readthedocs.io/en/latest/protocols.html#callback-protocols).

[mehdigmira]

I was not able to make it work with callable protocols either

from typing import Any

from typing_extensions import Protocol


class DecoratedF(Protocol):
    def __call__(self, a: str, *args: Any) -> None: ...


def g(f: DecoratedF): ...


@g
def f(a: str, b: str) -> None: ...

Am I doing smth wrong ?

[ilevkivskyi]

This is actually very similar to #5876 (see also a decorator example there). Which is opposite to the idea of callback protocols in some sense. Callback protocols allow to express signatures that are impossible to express using Callable syntax. However, there is something that can be expressed using Callable that can't be expressed as a signature, for example Callable[..., int] (with literal ...).

Potentially we can just also allow special meaning for *args: Any, **kwds: Any at the end of a signature to mean "I don't care" instead of "Should allow all possible calls".

[JukkaL]

We don't want to support a non-standard extension to the callable syntax, so proposed changes should go through the typing issue tracker or typing-sig@.