How to include conditional installs -- namely for backports

[thorwhalen]

Let's start with a concrete example.

It often happens that I want to use from importlib.resources import files, but that only exists in 3.9+.

In my code, I end up doing:

try:
    from importlib.resources import files  # ... and any other things you want to get
except (ImportError, ModuleNotFoundError):
    from importlib_resources import files  # pip install importlib_resources

But I feel shame when copy/pasting this code everywhere. Additionally, it still doesn't solve my problem "completely".
The question is: Do I include importlib_resources, a third-party backport of importlib.resources, in my setup.cfg install_requires? If I don't, my code will fail on python < 3.9. If I do include it, I'm overkilling my dependencies.

Ideally, I'd like a solution where I can just do

from importlib_resources import files

in my code, and trust that the setup.cfg took care of doing two things:

• telling the install to only do a pip install importlib-resources if python version < 3.9
• telling it that importlib_resources is an alias for importlib.resources if in 3.9+, and of importlib_resources (the pip install backport) if not.

Trying to solve the first problem only, I did this.

install_requires =
    dol
    importlib_resources; python_version < '3.9'

But it doesn't condition the install at all (it's installed on both 3.8 and 3.10!).

Not sure how to even start with the second "aliasing" desire.

[thorwhalen]

Posted the question to this stackoverflow question.