[BUG] Unable to pickle cpdef enum values from pure python because of attribute lookup error

[tarasko]

Describe the bug

pickle.dumps throws an exception when attempted to serialize enum value

>>> pickle.dumps(ValEnum.val1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
_pickle.PicklingError: Can't pickle <enum 'ValEnum'>: attribute lookup ValEnum on importlib._bootstrap failed

Code to reproduce the behaviour:

cpdef enum ValEnum:
    val1 = 1
    val2 = 2

import pickle
pickle.dumps(ValEnum.val1)

Expected behaviour

pickle.dumps should return serialized value instead of throwing an exception

Environment

OS: Linux 5.4.0-124-generic #140-Ubuntu SMP Thu Aug 4 02:23:37 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
Python version [e.g. 3.10.6]
Cython version [e.g. 3.0.0a11]

Additional context

No response

[tarasko]

I wonder if there is any easy workaround for this?

[da-woods]

Thanks for the report. I suspect we just need to pass module and/or qualname arguments when we construct the enum.

The workaround probably involves casting it to int and pickling the int I suggest.