fix usage of Matplotlib color maps

[mwageringel]

Matplotlib used to have a global dictionary of color maps. By now, it is considered internal API and does not contain newer color maps anymore, so some of them cannot be used in Sage:

sage: density_plot(x, (-1,1), (-1,1), cmap='turbo')
/usr/lib/python3.10/site-packages/sage/repl/rich_output/display_manager.py:608: RichReprWarning: Exception in _rich_repr_ while displaying object:
Color map turbo not known (type import matplotlib.cm; matplotlib.cm.datad.keys() for valid names)

CC: @tscrim @davidlowryduda

Component: graphics

Keywords: matplotlib

Author: Markus Wageringel

Branch: 2022ed6

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/33491

[mwageringel]

Branch: u/gh-mwageringel/33491

[mwageringel]

Commit: 2022ed6

[mwageringel]

Author: Markus Wageringel

[mwageringel]

comment:1

This branch obtains the colormaps from matplotlib.colormaps instead of matplotlib.cm.

I have removed the module-wide cm variable as I do not see a purpose of it. The code is more than 10 years old, so it is probably not related to modularization. My best guess is that it has to do with lazy imports in Python 2.

In the long run, we can also consider removing Sage's Colormaps collection and replace it by Matplotlib functionality, since Matplotlib already has support for registering new color maps.

---

New commits:

2022ed6

33491: fix usage of matplotlib colormaps

[tscrim]

comment:2

I agree that there is no reason to nail that in memory. This is a good step towards removing redundancy in Sage that can be achieved elsewhere. LGTM.

[tscrim]

Reviewer: Travis Scrimshaw

[mwageringel]

comment:3

Thank you.

[vbraun]

Changed branch from u/gh-mwageringel/33491 to 2022ed6

[tobiasdiez]

Changed commit from 2022ed6 to none

[tobiasdiez]

comment:5

On conda, one sees now the following error

sage.repl.rich_output.display_manager.RichReprWarning: Exception in _rich_repr_ while displaying object: cannot import name 'colormaps' from 'matplotlib' (/usr/share/miniconda/envs/sage-build/lib/python3.8/site-packages/matplotlib/__init__.py)

I think this may be introduced by this ticket, see https://github.com/sagemath/sage/runs/5800737359?check_suite_focus=true. (Not sure if it's only conda-related).

[mkoeppe]

comment:6

Sounds like build/pkgs/matplotlib/install-requires.txt should have been adjusted?
It says matplotlib >=3.3.1

[davidlowryduda]

comment:7

I think you're right. This seems to require matplotlib >= 3.5.0 (https://matplotlib.org/stable/users/prev_whats_new/whats_new_3.5.0.html#id13).

[mkoeppe]

comment:8

I've opened #33642 for this