Should `object.__hash__` be `Callable[[], int] | None` if `None` is a valid and common usage?

[KotlinIsland]

Currently you have to type: ignore it.

related: #3884

[srittau]

Everything we do about __hash__() is problematic, because of its Schrödinger's nature:

class Foo:
    pass
print(Foo().__hash__())  # prints an int

class Bar:
    def __eq__(self, other):
        return True
Bar().__hash__()  # `NoneType` object is not callable

I believe the best solution for this problem is to special-case type checkers so that __hash__: None is a valid construct in stubs and you don't need # type: ignore for that. I commented as such on python/mypy#11465.

[sobolevn]

Related python/mypy#11495