How to type annotate a binary operator?

[LeeeeT]

I have a code that defines a binary operator like this:

from __future__ import annotations

from dataclasses import dataclass


@dataclass
class MyClass:
    x: int

    def __add__(self, other: MyClass, /) -> MyClass:
        if isinstance(other, MyClass):
            return MyClass(self.x + other.x)
        return NotImplemented

Due to how binary operators work in python, I am forced to wrap the actual implementation in if isinstance block and return NotImplemented if the check fails.

This worked without errors prior to version 1.1.380. On version, 1.1.380 I'm getting this error:

file.py:11:12 - error: Unnecessary isinstance call; "MyClass" is always an instance of "MyClass"

So, my question is: how to properly type annotate __add__, given the special behavior of binary operators in python?

[erictraut]

Your code looks fine to me. You would need to suppress the reportUnnecessaryIsInstance error in this case.