A slightly more straightforward way to repro:

from typing import Any

class A:
    def f(self, o: Any) -> None:
        if isinstance(o, self.__class__):
            reveal_type(o)  # builtins.object

It should be fixable by changing typeshed:

class object:
    @property
    def __class__(self: _T) -> Type[_T]: ...

Seems to work (at least for this particular case).

    reveal_type(o)  # Revealed type is 'tmp.A*'

@elazarg I think that's a good fix. It should probably be combined with #3056.

@elazarg's proposed typeshed change isn't quite right because __class__ is writable. Though I suppose if you assign to __class__ there's little hope for typechecking your code. I'll try adding a setter.

This should be reopened since python/typeshed#1549 was reverted in python/typeshed#1632.

@gvanrossum I think the original PR can be simply re-applied, since the issue that caused reverting it should be fixed now.

Here is the PR python/typeshed#1951. I checked manually that it doesn't cause problems you mentioned in python/typeshed#1549 (comment) (will run testpr tomorrow).

@gvanrossum Unfortunately, there are still some problems with python/typeshed#1951, I will investigate next week.

Any luck with this one?

It would be great to have the insurance that __class__(self: _T) -> Type[_T]: ...

@mlhamel Unfortunately core mypy team is overloaded with other tasks plus two team members are on vacation now.

@ilevkivskyi no worries i was mostly just wondering if there was anything new but if i can help in any way I would be pleased to give a try

@mlhamel TBH I don't remember now what exactly was the problem with python/typeshed#1951 that should fix this. I just remember that there was some weird interaction with classes that have an Any base class. One thing you can help with is if you have some large code bases could you try locally applying python/typeshed#1951 and checking if there are any problems with it.