Generic class with ParamSpec isn't callable as far as partial is concerned

from collections.abc import Callable
from functools import partial
from typing import Generic, TypeVar

from typing_extensions import ParamSpec

R_co = TypeVar('R_co', covariant=True)
P = ParamSpec('P')

class X(Generic[P, R_co]):
    def __init__(self, f: Callable[P, R_co]):
        super().__init__()
        self.f = f

    def __call__(self, /, *args: P.args, **kwargs: P.kwargs) -> R_co:
        return self.f(*args, **kwargs)

@partial(X)  # error: Argument 1 to "partial" has incompatible type "Type[X[Any, Any]]"; expected "Callable[..., X[P, R_co]]"  [arg-type]
def f() -> int:
    return 2

print(f())

oddly, Mypy accepts X as a Callable[P, T_co] here—it's specifically Callable[..., T_co] that it's rejecting:

class X(Generic[P, T_co]):
    def __init__(self, func: Callable[P, T_co], /) -> None:
        self._func = func

    def __call__(self, *args: P.args, **kwargs: P.kwargs) -> T_co:
        return self._func(*args, **kwargs)


class badX(Generic[T_co]):
    # the same wrapper thing, but "typed" (really, half-typed) like :class:`~functools.partial`.
    def __init__(self, func: Callable[..., T_co], /) -> None:
        self._func = func

    def __call__(self, *args: Any, **kwargs: Any) -> T_co:
        return self._func(*args, **kwargs)


X(X)
badX(X)  # error: Argument 1 to "badX" has incompatible type "Type[X[Any, Any]]"; expected "Callable[..., X[P, T_co]]"  [arg-type]

(https://mypy-play.net/?mypy=1.1.1&python=3.11&gist=75162691fee56d70787ee7a94896a081)

The original example works on master, likely fixed by #15837

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Generic class with ParamSpec isn't callable as far as partial is concerned #14802

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Generic class with ParamSpec isn't callable as far as partial is concerned #14802

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gschaffner commented on Mar 23, 2023

ilevkivskyi commented on Aug 16, 2023

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