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

首先使用 mypy 0.761 重现两个 Python 代码片段，并比较两个 abs 返回注解如何影响 abs(x) 调用。跟踪 SupportsAbs 和 TypeVar 边界的类型检查路径；当带注解的版本不再像未带注解的版本一样产生 incompatible-argument 错误时即完成。