classonlymethod decorator/descriptor defined below is like the built-in classmethod, but you're not allowed to call the method on instances, only on the class itself. from typing import Concatenate, Self from collections.abc import Callable from functools import partial class classonlymethod[C, **P, R]: __slots__ = ( '_func', ) def __init__(self, func: Callable[Concatenate[type[C], P], R], /): self._func = func def __get__(self, instance: None, owner: type[C], /) -> Callable[P, R]: if instance is not None: raise AttributeError('class-only method') return partial(self._func, owner) class Foo: @classonlymethod def bar(cls: type[Self]) -> None: raise NotImplementedError() However, pyright complains on the definition of Foo.bar: Type of parameter "cls" must be a supertype of its class "Foo" (reportGeneralTypeIssues) Which is odd, since it matches annotations of classmethodin typeshed. I don't understand this error. Surely a Foo (denoted by Self) is a (non-strict) supertype of itself? I tried other ways to refer to Foo in the cls annotation, but they didn't work either. What's going on here and how do I fix it? Is it a pyright bug? Continue reading...
