Specifying the return type of `__abs__` to be a `TypeVar` causes `expected "SupportsAbs[<nothing>]` error

Specifying the return type of __abs__ to be a TypeVar causes expected "SupportsAbs[<nothing>] error

The following works fine:

from typing import TypeVar


T = TypeVar("T", bound="Number")


class Number:
    def __abs__(self: T):
        return self

    def square(self: T) -> T:
        return self


def myabs(x: T) -> T:
    return abs(x)


x = myabs(Number())
x.square()

But this produces an error:

from typing import TypeVar


T = TypeVar("T", bound="Number")


class Number:
    def __abs__(self: T) -> T:
        return self

    def square(self: T) -> T:
        return self


def myabs(x: T) -> T:
    return abs(x)


x = myabs(Number())
x.square()

• What is the actual behavior/output?

error: Argument 1 to "abs" has incompatible type "T"; expected "SupportsAbs[<nothing>]"

• What is the behavior/output you expect?

No error, like in the first example.

• What are the versions of mypy and Python you are using?

Python 3.6 and MyPy 0.761

Empieza reproduciendo ambos fragmentos de Python con mypy 0.761 y compara cómo afectan las dos anotaciones de retorno de abs a la llamada abs(x). Sigue el recorrido de comprobación de tipos para SupportsAbs y los límites de TypeVar; estará hecho cuando la versión anotada no produzca ningún error incompatible-argument como la versión sin anotar.