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

Inizia riproducendo entrambi gli snippet Python con mypy 0.761 e confronta l’effetto delle due annotazioni del valore restituito di abs sulla chiamata abs(x). Segui il percorso del controllo dei tipi per SupportsAbs e i bound di TypeVar; il lavoro è completato quando la versione annotata non produce alcun errore incompatible-argument come la versione non annotata.