Load entry points

The Python setup script provides entry points where objects can be assigned. In your main package, you can search for specific entry points and load them. Other package can also defined this entry point, so your main package will load them too. If you are interesting, I make a small video. Unfortunately, this video uses the old pkg_resources module.

With importlib.metadata, the new one:

>>> from importlib.metadata import entry_points
>>> for enp in entry_points()['axju.commands']:
...   print(enp.name)
...
django
info
show

The old one with pkg_resources:

>>> from pkg_resources import iter_entry_points
>>> for enp in iter_entry_points(group='axju.commands'):
...   print(enp.name)
...
django
info
show

Retrieving package version at run time

You can find this example on the readme file from setuptools-scm.

This is how you should do it, with importlib.metadata:

from importlib.metadata import version, PackageNotFoundError

try:
    __version__ = version("package-name")
except PackageNotFoundError:
    __version__ = 'Unknown'

And you'd better avoid that:

from pkg_resources import get_distribution, DistributionNotFound

try:
    __version__ = get_distribution("package-name").version
except DistributionNotFound:
    __version__ = 'Unknown'

However, this does place a runtime dependency on setuptools and can add up to a few 100ms overhead for the package import time.

Conclusion

As you can see, these are not major changes to the source code. So the problem are not the adjustments, but the fact you should read the release note. Shame on me, I don't read them very often. I only came across this while researching for my video. But even then I did get it after the video it was published.

The biggest source for my video was the post from Amir Rachum's Blog, which was written before the release of version 3.8. That's why he still used pkg_resources.