Consider making staticmethod and classmethod generic

[sobolevn]

Feature or enhancement

Typeshed defines staticmethod and classmethod as generics:

1. https://github.com/python/typeshed/blob/f6216ec6230aa51fe7e23afca30a8f5b18ace476/stdlib/builtins.pyi#L137
2. https://github.com/python/typeshed/blob/f6216ec6230aa51fe7e23afca30a8f5b18ace476/stdlib/builtins.pyi#L154

It makes sense, because they are very callable-like. However:

>>> staticmethod[int]
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    staticmethod[int]
    ~~~~~~~~~~~~^^^^^
TypeError: type 'staticmethod' is not subscriptable
>>> classmethod[int]
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    classmethod[int]
    ~~~~~~~~~~~^^^^^
TypeError: type 'classmethod' is not subscriptable

We should consider making them generics in runtime as well.

@AlexWaygood @JelleZijlstra thoughts?
If you agree, I have a PR ready.

Linked PRs

• gh-132457: make staticmethod and classmethod generic #132460

[IvanKirpichnikov]

Another thing I noticed is that some generics in typeshed are not actually generics.
For example, almost all objects in itertools.pyi and functools.pyi are generics, but only a few of them are actually generics.

I can provide a list of such objects. I am also ready to undertake this correction if it is approved.