Attempt to fix issue #43

[erocarrera]

This PR successfully silences the error so autoclass works with Python 3.9. I have not investigated the code in depth to be cable to guarantee it as a full solution.

[smarie]

This removal makes the python 2 test fail since this if/else statement is specifically for python 2. We should not modify this branch but rather try to understand why the main path fails lines 234-239

try:
            cls.__bases__ = new_bases
        except TypeError:
            try:
                # maybe a metaclass issue, we can try this
cls.__bases__ = with_metaclass(type(cls), *new_bases)
``

[erocarrera]

Thanks for pointing me in the right direction.
Under Python3.9, the code: cls.__bases__ = new_bases throws TypeError: __bases__ assignment: 'Mapping' deallocator differs from 'object' which I'm guessing might be the exception you're trying to catch.

The cls.__bases__ = with_metaclass(type(cls), *new_bases) throws TypeError: can only assign tuple to Experiment.__bases__, not metaclass (Experiment is the name of my class where I'm using autoclass)

I naively tried to make it a tuple as cls.__bases__ = (with_metaclass(type(cls), *new_bases),) and I get the exception TypeError: __bases__ assignment: 'temporary_class' deallocator differs from 'object'

I don't know what to try next, but maybe this gives you some information?

[smarie]

Thanks a lot for providing this ! Well this does not look good. I understand why you ended up fixing the last part of the try/except.

Not sure that I can fix this very soon. I'll have a look in the upcoming weeks.

If you wish to have a stab at it in between, you can try to

• revert the changes you did,
• create a boolean version flag (PY38 = sys.version_info >= (3, 8))
• use that flag in the last "except" (just where you did your first mod) to skip the method names that are not relevant anymore, and to not use .im_func.

Also note that a more recent lib that I consider better than autoclass for my personal use is https://smarie.github.io/python-pyfields/ . It also provides an @autoclass decorator. Instead of fiddling with the class bases, this decorator adds to_dict and from_dict methods.

Still of course I try to maintain both when possible

[erocarrera]

Hi Sylvain, I've moved to pyfields as you suggested, that solved the issue for me. I will not grapple with trying to address the issue in autoclass. Feel free to close the PR if you want.

[smarie]

Thanks a lot @erocarrera ! Sorry for not spotting your PR sooner.

As commented above, it seems that you modified a try/except branch that was dedicated to a special case of python 2... So the issue is rather to understand why the code on python 3.8+ enters this branch at all, in other words to understand why

cls.__bases__ = new_bases

fails in the first place.

[smarie]

(replying to #44 (comment) )

Perfect @erocarrera thanks for the feedback ! Indeed moving to pyfields when possible is probably a better choice. I did not yet found time to fix this autoclass issue, sorry :( we'll see if many users are interested or if they all move away to pyfields, attrs, dataclasses and the like