`singledispatchmethod.register` fails with `typing.Self` annotation

Bug report

Bug description:

When using singledispatchmethod, the register decorator function raises an exception if self is annotated with typing.Self:

TypeError: Invalid annotation for 'self'. typing.Self is not a class.

Minimal example:

from functools import singledispatchmethod
from typing import Self


class Foo:
    @singledispatchmethod
    def bar(self: Self, arg: int | str) -> int | str: ...

    @bar.register
    def _(self: Self, arg: int) -> int:
        return arg


foo = Foo()

print(foo.bar(1))

The workaround is to remove the typing.Self annotation for the _ function.

(Same for singledispatch but that should not be used in that case anyway)

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-130829
• gh-143465

functools.singledispatchmethod.registerから始め、Python 3.13で報告にある最小限の例を再現してください。先に既存のリンク先の作業を確認してください。例に対するリグレッションカバレッジを追加し、typing.Selfを使用するメソッドを無効なアノテーションによるTypeErrorを発生させずに登録できれば完了です。