python@3.8 3.8.0 (new formula)

[bayandin]

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• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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This PR adds python@3.8 formula and migrates 10 most popular depending on python formulae (but glib)

[Bo98]

Hmm might need to be careful and think about dependency trees here.

If a Python 3.7 formula depends on a Python 3.8 formula (or vice versa), there's gonna be problems. I'm not sure how many forumlae are in that situation.

One thing for sure is Cython. If we don't migrate everything depending on Cython together, we're gonna have to have two Cython formulae - one for Python 3.7 and one for Python 3.8. How many formulae are there depending on Cython?

[Bo98]

There's actually a lot less depending on Cython than I thought. We'll need to migrate that and their dependants (recursively) together, either now or later on.

[bayandin]

Here it is, the list of formulae recursively depending on cython as a formula or as a resource:

adios2
apache-arrow
apache-arrow-glib
arcade-learning-environment
astrometry-net
aubio
boost-python3
breezy
btfs
caffe
cassandra
cassandra@2.2
csound
dvc
gdal
gmt
gmt@5
graph-tool
liblas
libtorrent-rasterbar
mapnik
mapserver
mpi4py
numpy
ola
opencv
opencv@3
openimageio
osm2pgrouting
pdal
pgrouting
points2grid
postgis
scipy
simple-tiles
siril
urh
virtualpg
visp
wxpython

numpy@1.16
pytouhou
urh
vapoursynth
gnuradio
gr-osmosdr
opencv@2
mpv
mvtools
vapoursynth-imwri
vapoursynth-ocr
vapoursynth-sub

[Bo98]

As a resource doesn't really matter since updating the Cython formula won't mandate updating those that use Cython as a resource at the same time. As a formula it does matter. And it needs to be done recursively (except in cases where a formula doesn't use any Python at all): brew uses --include-build --include-test --recursive cython.

You then need to watch out if anything on that list depends on another Python formula that doesn't itself depend on Cython - that too will need to be updated. Not sure of a nice way to get such list.

Cython is just an example of course - there's others too.

[bayandin]

This PR will land python@3.8 formula only (because bumping the first 10 formulae from the list has eaten all the space on CI again)

[michaelblyons]

Can an owner add the [python] label to this PR?

[SMillerDev]

It doesn't really change anything but here you go

[OJFord]

Is there anything still needed here? I understand it's just step 1 in a larger effort to get to python being at 3.8, but this PR alone is helpful for people that want to use it directly, keeping old python around for any dependencies.

[iMichka]

I think we should add the caveats back (and adapt the paths in the caveat). Except that, everything looks good for me.

[bayandin]

Thanks @iMichka, added caveats back

[iMichka]

As this is keg_only, I guess that the pip3 path should also be something like #{HOMEBREW_PREFIX/"bin/pip3"} ?

[iMichka]

Let's merge this as-is once the build is done and green :)

[iMichka]

I'll open another PR to fix the caveats, I noticed that some information in there is wrong.

[iMichka]

Here is the PR to update the caveat: #47984

[bayandin]

Thanks @iMichka!

[chenrui333]

Good to see this move forward!!