ValueError: A colormap named "cet_gray" is already registered

[yannikschaelte]

Software version info

colorcet 3.0.1 arviz 0.12.1 python 3.10/8 matplotlib 3.6.0/1 afaik introduced with recent colorcet/matplotlib release

Description of expected behavior and the observed behavior

When multiple libraries use mpl.colormaps.register(cmap, name=cmap_name) with the same cmap_name, a ValueError: A colormap named "cet_gray" is already registered. is raised. This happens e.g. for colorcet + arviz, both of which define cet_gray (see here for arviz, here for colorcet).

Arviz appears here to emulate the colorcet color.

Is this an issue/responsibility of colorcet/arviz/...?

Complete, minimal, self-contained example code that reproduces the issue

import arviz
import colorcet

or

import colorcet
import arviz

This prohibits the use of both simultaneously.

Stacktrace

Traceback (most recent call last):
 File "<string>", line 1, in <module>
 File "/home/yannik/env/env/lib/python3.10/site-packages/arviz/__init__.py", line 320, in <module>
   _mpl_cm("gray", _linear_grey_10_95_c0)
 File "/home/yannik/env/env/lib/python3.10/site-packages/arviz/__init__.py", line 317, in _mpl_cm
   register_cmap("cet_" + name, cmap=cmap)
 File "/home/yannik/env/env/lib/python3.10/site-packages/matplotlib/_api/deprecation.py", line 200, in wrapper
   return func(*args, **kwargs)
 File "/home/yannik/env/env/lib/python3.10/site-packages/matplotlib/cm.py", line 248, in register_cmap
   _colormaps.register(cmap, name=name, force=override_builtin)
 File "/home/yannik/env/env/lib/python3.10/site-packages/matplotlib/cm.py", line 149, in register
   raise ValueError(
ValueError: A colormap named "cet_gray" is already registered.

[OriolAbril]

Maybe we can add a check and only register the cmap if colorcet is not installed? (so that both import orders work as opposed to checking if the cmap is registered and requiring arviz to be imported second) cc @aloctavodia

[ColCarroll]

Maybe wrapping in a try/except ValueError right here? It doesn't "commute" with import order, but I'll pop over to the colorcet side and see if maybe that should just be a best practice.

[ahartikainen]

Why do we use same name as colorcet?

[ColCarroll]

It is the same colorscale, so it makes sense from that perspective.

[ColCarroll]

Sounds like they are suggesting something similar to you, @OriolAbril ! https://github.com/holoviz/colorcet/issues/96#issuecomment-1276576516