enum.IntFlag (un)pickles incorrectly on Python 3.12 (and differently on Python 3.11)

[da-woods]

Bug report

Run the following code:

import enum
import pickle

class PxdEnum(enum.IntFlag):
    RANK_0 = 11
    RANK_1 = 37
    RANK_2 = 389

print(pickle.loads(pickle.dumps(PxdEnum.RANK_2)))

On Python 3.10.10 I get PxdEnum.RANK_2
On Python 3.11.2 I get 389 (which is probably also acceptable)
On Python 3.12 (0aaef83351473e8f4eb774f8f999bbe87a4866d7) I get

Traceback (most recent call last):
  File "<path>/enumpickle.py", line 9, in <module>
    print(pickle.loads(pickle.dumps(PxdEnum.RANK_2)))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unsupported operand type(s) for |: 'PxdEnum' and 'NoneType'

Your environment

Tested as described on Python 3.10, 3.11, and 3.12.
Linux

Linked PRs

• gh-105332: [Enum] Fix unpickling flags in edge-cases #105348
• [3.11] gh-105332: [Enum] Fix unpickling flags in edge-cases (GH-105348) #105519
• [3.12] gh-105332: [Enum] Fix unpickling flags in edge-cases (GH-105348) #105520

[sobolevn]

The same also happens with Flag as well:

import enum
import pickle

class PxdEnum(enum.Flag):
    RANK_0 = 11
    RANK_1 = 37
    RANK_2 = 389

d = pickle.dumps(PxdEnum.RANK_2)
print('--')
print(pickle.loads(d))

The offending commit is 5369858

I am working on a fix! Thanks for the report.

[sobolevn]

@da-woods in 3.11 only the representation was changed, it still gives Enum back:

Python 3.11.3 (main, May 27 2023, 12:23:35) [Clang 14.0.3 (clang-1403.0.22.14.1)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import enum
>>> import pickle
>>> 
>>> class PxdEnum(enum.IntFlag):
...     RANK_0 = 11
...     RANK_1 = 37
...     RANK_2 = 389
... 
>>> print(pickle.loads(pickle.dumps(PxdEnum.RANK_2)))
389
>>> print(type(pickle.loads(pickle.dumps(PxdEnum.RANK_2))))
<flag 'PxdEnum'>

[da-woods]

Thanks for the quick PR.

The change in representation wasn't a big worry - it didn't break anything for me. It was just something I spotted while preparing the checking the example and wasn't sure if it was relevant or not.