Would it be possible to broaden classmethod to accept ParamSpec when MyPy's support is better?

[NeilGirdhar]

It could be something like:

P = ParamSpec('P')
class classmethod(Generic[P, _R_co]):
    @property
    def __func__(self) -> Callable[P, _R_co]: ...
    @property
    def __isabstractmethod__(self) -> bool: ...
    def __init__(self: classmethod[_R_co], __f: Callable[P, _R_co]) -> None: ...
    def __get__(self, __obj: _T, __type: type[_T] | None = ...) -> Callable[P, _R_co]: ...
    if sys.version_info >= (3, 10):
        __name__: str
        __qualname__: str
        __wrapped__: Callable[P, _R_co]

[AlexWaygood]

This is on my to-do list for as soon as mypy 0.950 is released 🙂

[JelleZijlstra]

Though I'm not sure how much of a difference this will make, considering how thoroughly type checkers special case classmethod (and staticmethod).

[AlexWaygood]

Also, staticmethod is quite a lot easier than classmethod. staticmethod doesn't change the signature of the function it wraps, but classmethod does -- it requires Concatenate. It would be something like this:

import sys
from typing import TypeVar, Callable, Generic
from typing_extensions import ParamSpec, Concatenate

_P = ParamSpec("_P")
_R_co = TypeVar("_R_co", covariant=True)
_T = TypeVar("_T")

class classmethod(Generic[_P, _R_co, _T]):
    @property
    def __func__(self) -> Callable[Concatenate[_T, _P], _R_co]: ...
    @property
    def __isabstractmethod__(self) -> bool: ...
    def __init__(self: classmethod[_P, _R_co, _T], __f: Callable[Concatenate[_T, _P], _R_co]) -> None: ...
    def __get__(self, __obj: _T | None, __type: type[_T] | None = ...) -> Callable[_P, _R_co]: ...
    if sys.version_info >= (3, 10):
        __name__: str
        __qualname__: str
        @property
        def __wrapped__(self) -> Callable[Concatenate[_T, _P], _R_co]: ...

[NeilGirdhar]

@JelleZijlstra Yup, I just learned about that here. It's not too big a deal since it's very rare that you decorate class methods, but maybe after classmethod is broadened they might consider producing a classmethod[P, R, T] instead of a Callable[Concatenate[type[T], P], R].

[AlexWaygood]

Mypy 0.950 is now out, but sadly we still cannot use ParamSpec in classmethod or staticmethod due to https://github.com/python/mypy/issues/12011. (abc.abstractclassmethod and abc.abstractstaticmethod inherit from classmethod and staticmethod respectively, so while that mypy issue is outstanding, we cannot make builtins.staticmethod or builtins.classmethod generic over a parameter specification without breaking those two classes.)