Enum with str or int Mixin Breaking Change in Python 3.11

Bug report

Looks like there was a breaking change with the way str and int mixins work with Enums in Python 3.11:

from enum import Enum


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

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

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

The same goes for Enum classes with the int mixin.

In my project we were relying on Foo.BAR to return the enum value, so this change broke our code. We fixed it by replacing str Enum mixin with the newly added StrEnum class (thanks for that, it's exactly what we needed!).

I think reverting the breaking change would only introduce another breaking change so that's probably not the way to go. But maybe updating the whatsnew page and call out the change there could help people stumbling into this when doing the upgrade. I've found the existing point about this change in the release notes a little bit confusing and I have already opened a PR to try and clear it up a bit: #100387

I've also written a longer blog post about it here, and there has been some lively discussion in r/python.

Your environment

CPython versions tested on: 3.11.0, 3.11.1
Operating system and architecture: MacOS, Ubuntu 22.04

Linked PRs

@anze3db

@anze3db StrEnum was added in 3.11, does that work as a 'slot in' replacement for your use case?

docs: https://docs.python.org/3.11/library/enum.html#enum.StrEnum

@JosephSBoyle

@JosephSBoyle yes, we replaced the str mixin with StrEnum to fix this on our end. If we could let people know about this breaking change in the what's new docs it would save me a lot of head scratching, especially since the current note about this change seems wrong (see my attempt of at least making it a bit more accurate: #100387)

@anze3db

Coincidentally I've also used the mixin approach you describe in professional projects, which suggests that this use is at the very least not uncommon.

As such it makes sense that the docs also suggest a way to achieve the old behaviour, like you say @anze3db. I've added a small suggestion to your PR; hopefully that will help resolve things for others in the same position!

Thank you! The text that you added would have helped me a lot when I was figuring out how to fix this 👍

gh-100458: Clarify Enum.__format__() change of mixed-in types in the …

pythongh-100458: Clarify Enum.__format__() change of mixed-in types i…

[3.11] gh-100458: Clarify Enum.__format__() change of mixed-in types …

Merge branch 'main' into inlinecomp2

Tediously update all enum usages to use Enum.KEY.value instead of Enu…

Update and add support for 3.11 and 3.12 (#902)

Fix issue with enum test caused by breaking change in cpython

[dagster-helm] 3.11 str enum compat (#19113)

[dagster webserver] fix websockets on py3.11 (#19328)

Replace usage of Enum plus str mixin with StrEnum

Add support for Python 3.11

Update streams.py

📽️ Olive StrEnumBase IntEnumBase (#1290)

📽️ Olive StrEnumBase IntEnumBase (microsoft#1290)

fix breaking changes to new str-enum mixin behaviour in Py3.11

[buildkite] stop using str Enum (#25874)

fix(python 3.11): Python 3.11+ changed __str__ for enums

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Enum with `str` or `int` Mixin Breaking Change in Python 3.11 #100458

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Enum with str or int Mixin Breaking Change in Python 3.11 #100458

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JosephSBoyle commented on Dec 25, 2022

anze3db commented on Dec 27, 2022

JosephSBoyle commented on Dec 27, 2022

anze3db commented on Dec 27, 2022

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Enum with `str` or `int` Mixin Breaking Change in Python 3.11 #100458