Pickling is losing some fields on exceptions

[csm10495]

Bug report

Say we have an AttributeError with some fields on it (like name). When we pickle and unpickle it, we can see that .name (at least) is lost (and set to None). Optimally those fields should still be in-tact on the unpickled instance.

C:\Users\csm10495\Desktop>python
Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> a = AttributeError("test text", name="test name", obj="test obj")
>>> a.name
'test name'
>>> pickle.loads(pickle.dumps(a)).name
>>> pickle.loads(pickle.dumps(a))
AttributeError('test text')

Your environment

C:\Users\csm10495\Desktop>python --version
Python 3.11.0

C:\Users\csm10495\Desktop>ver

Microsoft Windows [Version 10.0.19045.2364]

C:\Users\csm10495\Desktop>

Same thing seems to happen on 3.10.7 and 3.11.3 as well.

Linked PRs

• gh-103333: Pickle the keyword attributes of AttributeError #103352

[csm10495]

Why don't values like name/obj appear in __dict__ for exceptions? I see that if that were the case, BaseException's default reduce should have worked out here.

[sobolevn]

It looks very related to #73652
If you agree, let's move there :)

[csm10495]

I think its the same overall problem, but i'm not really fit to come up with the be-all-end-all solution to the problem for all exceptions and their fields. (Which is where that issues seems to point).

For now I'd like to just try to fix this for AttributeError (if that's ok)... i've raised #103352 if you could check it.

[gpshead]

Thanks for the contribution, merged! I'm considering this a feature and doing it for 3.12 only as it can be seen as an API enhancement otherwise so doing this mid-cycle in 3.11 unless it were a regression from past releases doesn't feel right.

@sobolevn is right that there is a larger all Exceptions issue that could be dealt with, but this is still a meaningful improvement in the interim.