Allow self: Self for backwards compatability

[SimpleArt]

Bug Report

Using self: Self or cls: type[Self] results in an error.

To Reproduce

from typing import Self


class A:

    def foo(self: Self) -> Self:
        return self

Expected Behavior

The behavior should be equivalent to the workaround explained in PEP 673 before we had typing.Self. Users which previously used the old code would otherwise have to change all of the code which used the previous workaround to work with the new change or continue to use the old workaround.

# Should be a simple change to `from typing import Self`.
from typing import TypeVar
Self = TypeVar("Self", bound="A")


class A:

    def foo(self: Self) -> Self:
        return self

Actual Behavior

main.py:6: error: Variable "typing.Self" is not valid as a type  [valid-type]
main.py:6: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases

Requires self: Self to be changed to just self everywhere.

Your Environment

mypy Playground

[AlexWaygood]

Are you using mypy master? Mypy doesn't support typing.Self yet in any released version, so if you're using mypy 0.991 or older, that's why you're seeing the error. It will support typing.Self in the way you'd like it to in the next release (mypy 1.0).

[AlexWaygood]

(Follow #13685 for updates on the release schedule.)

[SimpleArt]

Thanks, I was testing in the linked mypy Playground. Checking back on it with the other versions, you're right in that the master branch works as expected, while every other version failed.