NumPy master failed to build on Python 3.10.beta.1

[fangchenli]

pandas started testing against Python 3.10 dev. We use pip install git+https://github.com/numpy/numpy.git to install NumPy in the CI. NumPy built successfully on Python 3.10.alpha.7, but it started failing on Python 3.10.beta.1, which was released yesterday.

CI link: https://github.com/pandas-dev/pandas/runs/2502353399

xref pandas-dev/pandas#41313

[seberg]

Oh, that double hash changes landed in CPython now, so we have to address gh-18833. But I guess the report also says which python version to condition that on, so should be quick.

[seberg]

@fangchenli I am a bit confused, I just tried locally and Python reports a7, although I guess I tried off the dev branch, so a7 definitely works without modification? Otherwise, I will go with >a6 for now and if someone notices (unlikely...) we can change it to >a7...

[fangchenli]

@seberg Yes, a7 works without modification. And we pined it to a7 for now.
For reference: https://github.com/pandas-dev/pandas/blob/master/.github/workflows/python-dev.yml

[seberg]

Oh, the tag didn't work, I updated it, the next nightly will be fine (I think they are bi-weekly, so it will be soon).

[charris]

(I think they are bi-weekly, so it will be soon)

There were two builds, travis (arm64) and azure (the rest), running on different days. I set both to run early Sunday mornings UTC.