MAINT: set Python version for 1.21.x to <3.11

[rgommers]

Note that SciPy has a more elaborate method here, using IS_RELEASE_BRANCH. Given that we're switching away from setup.py at some point and the ship kind of has sailed for 1.21.x already, I don't want to replicate that logic here.

[charris]

I plan on adding Python 3.10 to a future 1.21 release.

[rgommers]

I plan on adding Python 3.10 to a future 1.21 release.

This constraint is just meant to match whatever the release notes say. Which admittedly is a bit ambiguous right now:

The Python versions supported for this release are 3.7-3.9. Official
support for Python 3.10 will be added when it is released.

Did you mean for 1.21.0 upload wheels later, assuming they work without a patch? Or for 1.21.1 or up?

[charris]

I'll release 1.21.1 this weekend. Python 3.10 is scheduled for 10/04 + 1-3 weeks to be available on azure, so probably will be supported in NumPy 1.21.4-5. Given the offset in Python and NumPy release cycles, I expect that sort of timing will persist. I like to keep the Python support up to date in a given release cycle because I suspect that distros like fedora will update both python and numpy in their spring releases.

[rgommers]

I'll release 1.21.1 this weekend. Python 3.10 is scheduled for 10/04 + 1-3 weeks to be available on azure, so probably will be supported in NumPy 1.21.4-5.

Okay, then I think this is fine to merge. And it can be bumped to <3.11 for the first release in which we plan to support Python 3.10 - it's a minor thing in this case, but setting the upper limit matching the actual supported versions is a good habit.

[charris]

Is 3.10.0b3 < 3.10 ?

I'm not sure. It should be, but it depends on the version comparison function used. Let's see what CI says.

[charris]

Close/reopen to see if 3.10.0b3 tests run. That test was added after this PR was made.

[charris]

The 3.10.0b3 test runs. Thinking about it, how about using <= 3.10?

[rgommers]

Thinking about it, how about using <= 3.10?

All right, since we have CI for 3.10 we may as well lie a little bit and let people build these releases from source.

Making it <3.11, since < is better than <= here I think (3.10.1 may not be <= 3.10)

[rgommers]

Let's only add the trove classifier (Programming Language :: Python :: 3.10) for the version with wheels though.

[charris]

Thanks Ralf.