Removed usage of deprecated pkg_resources

[sliverc]

Fixes #503

pkg_resources is deprecated and should not be used anymore. We encountered this in our CI see django-json-api/django-rest-framework-json-api#1146

The version is now defined in polymorphic/__init__.py and setup.py extracts it from there. This way, there is also no need for setuptools to be installed when using django polymorphic.

[markgras]

A few things:

1. Did you give the attr: directive a try in setup.cfg? I think that that would be a cleaner drop-in replacement, would be less prone to error than a custom regex, and would keep all project metadata in setup.cfg instead of splitting it up between that and setup.py. Reference.
2. PEP 396 has been rejected, so perhaps the best solution here is actually to make a breaking change and remove the __version__ attribute in __init__.py altogether.

[sliverc]

Thanks @markgras for the hinter. I wasn't aware of attr directive. I have updated it accordingly. Furthermore, I added a version synonym for backwards compatibility, but if the maintainers decide this is not needed I am happy to remove it as well.

[markgras]

Happy to help! The module attribute being accessed can have any name. In your new commit you could assign the version string to __version__ directly and then access that attribute in setup.cfg if you'd like. I believe that setuptools' example purposely doesn't use a dunder variable so as to not unintentionally imply that the rejected PEP 396 should be followed.

[sliverc]

Just as an update. Python 3.12 removed pkg_resources, so it is not possible to use django-polymorphic anymore with Python 3.12. This PR fixes this as well. Great if it could get merged.

[alphatownsman]

ran into this in python 3.12 as well. thanks for fixing it. hope we can get a release soon.

[martin-thoma]

polymorphic/init.py:9: DeprecationWarning: pkg_resources is deprecated as an API

The last release is from 2021: https://pypi.org/project/django-polymorphic/#history , but in this repository are many updates.

Is djanog-polymorphic dead (on pypi)?