AttributeError in 3.11 on repr() of enum member if the enum has a non-Enum EnumType parent

[vashek]

Bug report

In CPython 3.11.0 - 3.11.2 (but not 3.10.10), I get a weird AttributeError when repr() is called on an Enum member of a class that was defined using multiple inheritance. Minimal code to reproduce:

from enum import Enum, EnumMeta

class _EnumSuperClass(metaclass=EnumMeta):
    pass

class E(_EnumSuperClass, Enum):
    A=1

print(repr(E.A))

With Python up to 3.10, the output is:

<E.A: 1>

With Python 3.11, the output is:

Traceback (most recent call last):
  File "C:\devel\tmp\api\e.py", line 9, in <module>
    print(repr(E.A))
          ^^^^^^^^^
  File "C:\Program Files\Python311\Lib\enum.py", line 1169, in __repr__
    return "<%s.%s: %s>" % (self.__class__.__name__, self._name_, v_repr(self._value_))
                                                                  ^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python311\Lib\enum.py", line 1168, in __repr__
    v_repr = self.__class__._value_repr_ or repr
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: type object 'int' has no attribute '_value_repr_'

Your environment

Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32
(But reproduced also on 3.11.2)

Linked PRs

• gh-102558: Fix AttributeError or repr() of enum member #102601
• [3.11] gh-102558: [Enum] fix AttributeError during member repr() (GH-102601) #102977
• gh-102558: [Enum] better handling of non-Enum EnumType classes #103060
• [3.11] gh-102558: [Enum] better handling of non-Enum EnumType classes (GH-103060) #103064

[vashek]

Reproduced also on Linux in case it's important: Python 3.11.2 (main, Mar 1 2023, 14:46:02) [GCC 10.2.1 20210110] on linux

[vashek]

Wow, this must be the fastest fix I've ever seen implemented in response to a random dude's complaint in the history of paid SLA contracts. Oh wait, I don't have any contract. Kudos and thanks.

[corona10]

@ethanfurman
I submitted the patch but not sure it is the correct fix(closer to work around)
So please let me know if you have a better fix. (or you can direct fix this)

[ethanfurman]

Merging in the work-around; will investigate further as time allows.

[ethanfurman]

@vashek What is your actual use-case for that coding style? Making a non-Enum class with EnumMeta as the type is not the intended usage.

[vashek]

@ethanfurman Now I feel a bit silly, because it seems like I brought it upon myself completely needlessly and wasted your time. Sorry.

What I'm doing is I have a class with some class methods for enums, and then I'm mixing it into the actual enums. I guess when I did that, my thought process was "if I'm going to mix in another class into the enum, and the enum has a special metaclass, surely I can't just use an ordinary class with its ordinary metaclass -- surely the mixed-in classes must have a common metaclass". Now that I googled and read up on the subject, I think I now understand that this would have only been a problem if my base class used a different metaclass. I don't remember whether I had ever tried it without the metaclass -- maybe I haven't. I tried now and it seems to work fine.

I mean the fix is still nice, but I suppose the "bug" was only ever encountered by me and completely unnecessarily anyway, apparently.

[ethanfurman]

No worries, glad it ended up being an easy fix for us both.

[hauntsaninja]

Thanks, looks like this was fixed and backported!