Update colormap usage documentation to prioritize string colormap names #29028

Kaustbh · 2024-10-27T20:04:11Z

This update suggests using string colormap names directly for cmap arguments due to their readability and ease of use. The update also recommends plt.colormaps[name] to retrieve colormap instances, offering a scalable approach that supports both built-in and user-registered colormaps.

timhoffm

@Kaustbh Sorry, I have not been clear on the intended change in #28915.

With the recommendation

So the recommendation would be:

Use str colormap names on cmap arguments.

Use plt.colormaps[name] to get the colormap instance.

I primarily intended to change the way we access colormaps in the documentation; i.e. demonstrate by example. The concrete action is: "Go through our docs and apply these rules."

I'm a bit torn whether it's worth to spell the recommendations out explicitly for the user. While it gives direction, it's one more think to read/learn. Also, there's no canonical place to put that recommendation. It certainly does not belong in the diverging_colormaps what's new entry - that link was only where I saw the plt.cm* use.

Kaustbh · 2024-10-28T03:42:59Z

Okay, I will give it a try.

Kaustbh · 2024-12-03T17:28:42Z

Hi @timhoffm while going through the documentation I saw an example, https://matplotlib.org/stable/gallery/mplot3d/imshow3d.html#sphx-glr-gallery-mplot3d-imshow3d-py, in this example code,
we are using colors = plt.get_cmap(cmap)(norm(array)), when I changed it to colors = plt.colormaps[cmap](norm(array)), I was getting the error,

raise KeyError(f"{item!r} is not a known colormap name") from None

KeyError: 'None is not a known colormap name'

which caused because we are having cmap=None in the imshow3d function, how should I solve this problem.
And should I work on changing all the occurences in the docs?

timhoffm · 2024-12-03T18:28:29Z

Please leave this as is for this PR - it’s off-topic.

(General note: plt.get_cmap() will continue to be valid and is an alias of matplotlib.colormaps.get_cmap(), which in contrast to item access resolves None to the default colormap.)

Kaustbh · 2024-12-03T20:10:00Z

Thank you for the clarification! I understand that plt.get_cmap() will remain valid and resolve None to the default colormap. I wanted to confirm: should I proceed with replacing all occurrences of plt.cm.* with the recommended syntax (cmap="name" or plt.colormaps[name]) as part of this PR?

timhoffm · 2024-12-03T20:32:42Z

should I proceed with replacing all occurrences of plt.cm.* with the recommended syntax (cmap="name" or plt.colormaps[name]) as part of this PR?

Yes.

Kaustbh · 2024-12-08T08:27:18Z

I have made the commit please review and suggest me any changes.

lib/matplotlib/tests/test_image.py

galleries/users_explain/colors/colorbar_only.py

galleries/examples/specialty_plots/leftventricle_bullseye.py

galleries/examples/specialty_plots/advanced_hillshading.py

galleries/examples/showcase/mandelbrot.py

galleries/examples/images_contours_and_fields/layer_images.py

galleries/examples/images_contours_and_fields/contourf_demo.py

doc/users/next_whats_new/diverging_colormaps.rst

timhoffm

Almost good to go. Please still fix the flake8/precommit errors. - The failing test on OSX is unrelated.

timhoffm · 2024-12-14T08:17:54Z

Pre commit isort fails. I don’t see directly what is wrong in the code. Can you please check what code changes it suggests?

QuLogic · 2024-12-17T00:20:09Z

Why are 132 files changed? Please don't changed unrelated files.

Kaustbh · 2024-12-17T05:04:54Z

I think it happened because of isort . command, can you please tell how can I fix this?

timhoffm · 2024-12-17T08:33:41Z

I assume, you have triggered isort locally and added all changes it has found? While I don't know why there are that many changes (maybe an update to isort?) these should not be part of this PR. We only want changes that are necessary in the context of this PR.

Before your last force-push there have been two or three isort errors in the precommit action. Please do the following:

go back to that state (use git reflog if necessary)
apply only the necessary isort changes for this PR. To do so, either:
- force push the old version again to see what the original error was, only run isort on the mentioned files
- run isort on the changed files in your commit. - Likely the simplest way to do this is to setup precommit locally https://matplotlib.org/devdocs/devel/development_setup.html#install-pre-commit-hooks

rcomer · 2024-12-17T12:49:10Z

pre-commit is configured to only run isort on three galleries

matplotlib/.pre-commit-config.yaml

Lines 63 to 68 in f8900ea

    
           - repo: https://github.com/pycqa/isort 
        
             rev: 5.13.2 
        
             hooks: 
        
               - id: isort 
        
                 name: isort (python) 
        
                 files: ^galleries/tutorials/|^galleries/examples/|^galleries/plot_types/

rcomer · 2024-12-19T16:59:46Z

If I have understood, all your deliberate changes are under galleries and all your non-deliberate changes are under lib. If that is correct, I think you can revert without resorting to reflogs:

git checkout HEAD~1 lib

This checks out the lib directory from the commit before the current one (HEAD~1).

QuLogic · 2024-12-24T00:01:56Z

galleries/examples/lines_bars_and_markers/multivariate_marker_plot.py

@@ -39,7 +39,7 @@
    t = Affine2D().scale(skill).rotate_deg(takeoff)
    m = MarkerStyle(SUCCESS_SYMBOLS[mood], transform=t)
    ax.plot(pos[0], pos[1], marker=m, color=cmap(thrust))
-fig.colorbar(plt.cm.ScalarMappable(norm=Normalize(0, 1), cmap=cmap),
+fig.colorbar(plt.cm.ScalarMappable(norm=Normalize(0, 1), cmap="plasma"),


Now the cmap variable in unused here, but still on the line above, so you should change cmap instead of this line.

QuLogic · 2024-12-24T00:05:45Z

galleries/examples/specialty_plots/leftventricle_bullseye.py

@@ -104,19 +104,19 @@ def bullseye_plot(ax, data, seg_bold=None, cmap="viridis", norm=None):

 # Set the colormap and norm to correspond to the data for which
 # the colorbar will be used.
-cmap = mpl.cm.viridis
+cmap = mpl.colormaps["viridis"]


cmap is now unused, and should be removed (as well as the comment about it.)

QuLogic · 2024-12-24T00:06:11Z

galleries/examples/specialty_plots/leftventricle_bullseye.py

             cax=axs[0].inset_axes([0, -.15, 1, .1]),
             orientation='horizontal', label='Some units')


 # And again for the second colorbar.
-cmap2 = mpl.cm.cool
+cmap2 = mpl.colormaps["cool"]


Also unused and should be deleted.

QuLogic · 2024-12-24T00:08:21Z

lib/matplotlib/tests/test_colors.py

@@ -108,7 +108,7 @@ def test_double_register_builtin_cmap():


 def test_colormap_copy():


This test is about the Colormap class; you should not be replacing it with strings.

timhoffm reviewed Oct 27, 2024

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Update colormap usage documentation to prioritize string colormap names

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Update colormap usage documentation to prioritize string colormap names #29028

Update colormap usage documentation to prioritize string colormap names #29028

Kaustbh commented Oct 27, 2024

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QuLogic Dec 24, 2024

		@@ -108,7 +108,7 @@ def test_double_register_builtin_cmap():


		def test_colormap_copy():

Update colormap usage documentation to prioritize string colormap names #29028

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Update colormap usage documentation to prioritize string colormap names #29028

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