replace-str-enum (UP042)

Derived from the pyupgrade linter.

Fix is sometimes available.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for classes that inherit from both str and enum.Enum.

Python 3.11 introduced enum.StrEnum, which is preferred over inheriting from both str and enum.Enum.

import enum


class Foo(str, enum.Enum): ...

Use instead:

import enum


class Foo(enum.StrEnum): ...

Python 3.11 introduced a breaking change for enums that inherit from both str and enum.Enum. Consider the following enum:

from enum import Enum


class Foo(str, Enum):
    BAR = "bar"

In Python 3.11, the formatted representation of Foo.BAR changed as follows:

# Python 3.10
f"{Foo.BAR}"  # > bar
# Python 3.11
f"{Foo.BAR}"  # > Foo.BAR

Migrating from str and enum.Enum to enum.StrEnum will restore the previous behavior, such that:

from enum import StrEnum


class Foo(StrEnum):
    BAR = "bar"


f"{Foo.BAR}"  # > bar

As such, migrating to enum.StrEnum will introduce a behavior change for code that relies on the Python 3.11 behavior.