Replace use of build/bin/sage-python23 by just python3

[mkoeppe]

After the removal of python2 support, this script always calls $SAGE_LOCAL/bin/python3.

This simplification will help with implementing #29013.

[mkoeppe]

​https://trac.sagemath.org/ticket/30899#comment:55 explains why replacing it with plain python3 is correct.

[gh-tobiasdiez]

New commits:

​218fe09	Use system python for generation of conway_polynomials and elliptic_curves
​9f15544	Use python3 instead of system-python

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​f7323ee	Merge branch 'develop' of git://github.com/sagemath/sage into public/build/sharedSystemPython
​7cb43a5	Remove other instances of sage-python23

[gh-tobiasdiez]

I've now replaced all instances of sage-python23, and deleted the script itself. Ready for review.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​df2822c

Update documentation regarding use of python3 vs. sage-bootstrap-python

[mkoeppe]

I've revised the documentation a bit.

[gh-tobiasdiez]

Thanks, LGTM!

[mkoeppe]

This works well for me, but as this ticket removes the safety check that would stop a python package that forgot to include $(PYTHON) in dependencies from picking up the wrong python3 from somewhere else in the path, other developers should take a look if this is acceptable to them

[gh-tobiasdiez]

I would appreciate if this ticket could be reviewed. Thanks!

[jhpalmieri]

In the ​installation guide, do we need to remove the option to use Python 2.7? Or is that not related to this ticket?

[mkoeppe]

The minimal build requirements listed there are regarding sage-bootstrap-python, which is unrelated to this ticket.

[mkoeppe]

Update of this line of the installation guide now in #31192.

[jhpalmieri]

In principle it looks fine to me. How widely has it been tested?

• with Sage's Python 3?
• on systems with Python 3 (linux, OS X, OS X + homebrew)?
• on systems with only Python 2? (Should not be an issue, but should be tested anyway.)
• are there other configurations that need testing?

[gh-tobiasdiez]

I've tested it on Ubunut 20.10 (via WSL) and python 3 system.

[jhpalmieri]

Unfortunately I am currently unable to build Sage on my OS X Catalina machine using homebrew's Python, and this makes it hard for me to test this. As I said before, in principle it looks fine, so if others have tested it on a variety of platforms, I would be happy with a positive review.

[dimpase]

lgtm

[gh-tobiasdiez]

Thanks!