Pass python_requires argument to setuptools

[jdufresne]

Helps pip decide what version of the library to install.

https://packaging.python.org/tutorials/distributing-packages/#python-requires

If your project only runs on certain Python versions, setting the
python_requires argument to the appropriate PEP 440 version specifier
string will prevent pip from installing the project on other Python
versions.

https://setuptools.readthedocs.io/en/latest/setuptools.html#new-and-changed-setup-keywords

python_requires

A string corresponding to a version specifier (as defined in PEP 440)
for the Python version, used to specify the Requires-Python defined in
PEP 345.

[carltongibson]

First thought on this is "Yep, 👍, why not?"

Then I think:

• I need to check the syntax, but is an opt-in list not shorter, especially as we go on?
• Blue-skies: can we combine this somehow with maintaining the list of trove classifiers below.

I have a pet peeve with forgetting to update the supported versions in ≈3 or 4 different places; it would be nice to do something about that. (As I say "Blue-skies")

[rpkilby]

Blue-skies: can we combine this somehow with maintaining the list of trove classifiers below.

Writing some code here seems like it would be overly complicated. Maybe we can just add it to the release process checklist? eg,

• Update supported versions:
  • setup.py python_requires list
  • setup.py Python & Django version trove classifiers
  • README Python & Django versions
  • docs Python & Django versions
  • ...

[carltongibson]

...would be overly complicated...

Well, would it? (Maybe, yes.)

I use bumpversion on django-filter and it's great. At the back of my mind I have the thought that something similar would be good here (and for the README, and anywhere we maintain the exact same list of supported versions — Oh, yes, I see you covered those in your checklist @rpkilby 🙂)

I think updating the Release Process checklist with this would be a good addition pending any super code solution.

[jdufresne]

I made the suggested docs edits. Please let me know if I interpreted the intentions correctly, that the change is in the right place, and is acceptable wording. Thanks.

[carltongibson]

OK. That's great. Lets have it! 👍