enum class cannot be generic (class creation fails with `TypeError`) - Ruff

What it does

Checks for enum classes that are also generic.

Why is this bad?

Enum classes cannot be generic. Python does not support generic enums: attempting to create one will either result in an immediate TypeError at runtime, or will create a class that cannot be specialized in the way that a normal generic class can.

Examples

toml

[environment]
python-version = "3.12"

python

from enum import Enum
from typing import Generic, TypeVar

T = TypeVar("T")


# enum class cannot be generic (class creation fails with `TypeError`)
class E[T](Enum):  # error
    A = 1


# enum class cannot be generic (class creation fails with `TypeError`)
class F(Enum, Generic[T]):  # error
    A = 1


# enum class cannot be generic -- the class creation does not immediately fail...
class G(Generic[T], Enum):  # error
    A = 1


# ...but this raises `KeyError`:
x: G[int]

References

Python documentation: Enum