Wheel test broken

Hmm wheels_universal failure unrelated, investigating. @epassaro what do you think?

Seems Azure (the OA template to be precise) is installing and running Python 3.9 but poliastro is set ❤️.9. See this line.

_Originally posted by @epassaro in https://github.com/poliastro/poliastro/pull/1034#issuecomment-710503295_

[astrojuanlu]

@epassaro … I think we were only missing this! https://github.com/OpenAstronomy/azure-pipelines-templates/commit/0ba9adf763 (we were still using your fork, I amended this in gh-1060)

[astrojuanlu]

Hi @saintaardvark !

If there is anything we can do to help test poliastro on 3.9, please let me know

In principle, if you get Numba to install on Python 3.9, poliastro should work without problems. We were waiting for the project to provide manylinux wheels (that way we avoid having to compile llvmlite against LLVM), which should happen around mid-December as per https://github.com/numba/numba/issues/6345#issuecomment-721738251.

The other reason why we set poliastro to require Python 3.9 is… because people don’t know how to use pip 😃 They will install Python 3.9, try pip install poliastro, see a huge red wall of text, and complain here. I’ve seen this in other projects, and unfortunately pip (or numba, or llvmlite, whatever) do not provide a nice error message saying " ✨ Howdy! You are trying to install a package that requires compiling some binary extensions, but apparently you don’t have the necessary dependencies in your operative system, and this failed ✨ ".

I’m tracking 3.9 support here https://github.com/poliastro/poliastro/pull/1027 when this pull request passes, I will declare that poliastro is compatible with Python 3.9.

But again: if you care enough and have a lot of determination and you want to test poliastro on Python 3.9, you can help us by:

1. creating a new environment,
2. compiling numba in it,
3. removing the <3.9 requirement from poliastro pyproject.toml,
4. installing it from source, and
5. running the tests.

Let us know if you have any issues!