singledispatchmethod.register fails with typing.Self annotation

[bvolkmer]

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-130827: Support typing.Self annotations in singledispatchmethod() #130829

[ZeroIntensity]

Presumably, we want to:

• Disallow Self on singledispatch.
• But allow it on singledispatchmethod.

That seems easy enough, but we'll probably need a new internal helper to hide any talking between singledispatch and singledispatchmethod. I'll submit a fix.