[Python] functools.singledispatchmethod with own class as arg type

I would like to use functools.singledispatchmethod to overload the binary arithmetic operator methods of a class called Polynomial. The problem I have is that I can't find a way to register method calls where other is a Polynomial.

Perhaps better explained with a simple example:

from __future__ import annotations
from functools import singledispatchmethod


class Polynomial:
@singledispatchmethod
def __add__(self, other):
return NotImplemented

@__add__.register
def _(self, other: Polynomial):
return NotImplemented


The code above raises a NameError:

NameError: name 'Polynomial' is not defined


This NameError is not caused by the annotation but is raised inside functools. Also, annotating using a string 'Polynomial' instead without the need of __future__.annotations doesn't work either. This behavior is not documented in the documentation for functools.singledispatchmethod.

I can make it work by making Polynomial inherit from another class, and then using that class in the type annotation:

from functools import singledispatchmethod


class _Polynomial:
pass


class Polynomial(_Polynomial):
@singledispatchmethod
def __add__(self, other):
return NotImplemented

@__add__.register
def _(self, other: _Polynomial):
return NotImplemented


..but I am not overly fond of this solution.

How can I make this work without needing the useless intermediate class?

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