Summary

This was reported on Discord:

import abc
import typing
from typing import Generic

import typing_extensions

_Caps = typing_extensions.TypeVar("_Caps", bound=int | str, contravariant=True, default=int | str)


class CameraConnection(typing.Generic[_Caps]):  # okay
    pass


class Camera(Generic[_Caps], metaclass=abc.ABCMeta):  # UP046 false positive
    pass

In short, UP046 was suggesting to use PEP-695 type parameters in the second class on Python versions before 3.13 despite _Caps using a default, which is only supported in PEP-695 type parameters on 3.13 and later.

The fix looks unrelated at first glance, but this early return was preventing the diagnostic from being defused later for having a default.

Test Plan

New test derived from the report