Support for Python 3.9

Dear @FrancescAlted, @robbmcleod and @pydata,

first things first: Thank you so much for conceiving and maintaining NumExpr.

Binary wheels for Python 3.9 for all of lxml, h5py, Pandas and Numpy are already available on PyPI these days. At @earthobservations, we just have been able to upgrade to their most recent releases on Wetterdienst and it works like a charm, see https://github.com/earthobservations/wetterdienst/pull/202#issuecomment-727190718.

For PyTables, we also just outlined the situation at https://github.com/PyTables/PyTables/issues/823.

It would be awesome if you could also build and upload cp39 artefacts to PyPI to make it easier for downstream packages and their users to upgrade to Python 3.9.

With kind regards, Andreas.

[mattip]

A couple of hints: cibuildwheel is a nice way to build wheels, they support github actions among other options. You may want to think about an arm64 wheel: github actions is x86-only. NumPy uses travis-ci.com (since they also have ppc64 and s390x) and shippable.com (for arm64 only). And if you end up using cibuildwheel, a pypy wheel should JustWork. If not, please report a bug to pypy at https://foss.heptapod.net/pypy/pypy/-/issues

[robbmcleod]

After looking into it further I’m quite keen to switch to GitHub Actions instead of using Appveyor/Travis. I’ll probably figure out how to do it first for my cpufeature package (so I don’t spam all the watchers here with commits). If you want to follow along I’ve made a new issue to track it:

https://github.com/robbmcleod/cpufeature/issues/7

It looks like we’ll be able to have separate actions for pushes versus releases, so tests and wheel builds all in this repo should be possible (making numexpr-wheels defunct).