[Bug]: ValueError: The truth value... when an ndarray is passed to the color kwarg of axes3d.scatter

[joshuacwnewton]

Bug summary

Passing a numpy array to the color argument of ax.scatter results in a ValueError when ax is initialized with projection='3d'. This error began occurring in our CI after the release of matplotlib 3.8.0.

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
ax.scatter(1, 0, 0, color=np.array([0, 0, 0, 1]))
plt.show()

Actual outcome

Traceback from our CI suite:

  File "/home/runner/sct_6.1.dev0/testing/cli/test_cli_sct_dmri_display_bvecs.py", line 17, in test_sct_dmri_display_bvecs_png_exists
    sct_dmri_display_bvecs.main(argv=['-bvec', sct_test_path('dmri', 'bvecs.txt')])
  File "/home/runner/sct_6.1.dev0/spinalcordtoolbox/scripts/sct_dmri_display_bvecs.py", line 176, in main
    ax.scatter(x[i], y[i], z[i], color=shell_colors[bvals[i]], alpha=0.7)
  File "/home/runner/sct_6.1.dev0/python/envs/venv_sct/lib/python3.9/site-packages/matplotlib/__init__.py", line 1465, in inner
    return func(ax, *map(sanitize_sequence, args), **kwargs)
  File "/home/runner/sct_6.1.dev0/python/envs/venv_sct/lib/python3.9/site-packages/mpl_toolkits/mplot3d/axes3d.py", line 2377, in scatter
    if kwargs.get('color', None):
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Expected outcome

No error.

Additional information

NB: This is legacy code I'm maintaining but haven't actually written myself -- I only began looking at it after our CI threw an error after the upgrade from matplotlib 3.7.3 to 3.8.0.

• If I remove projection='3d', the code does not error out.
• If I pass a list ([0, 0, 0, 1]) rather than an ndarray, the code does not error out, and displays a black, opaque point:

Operating system

Ubuntu 22.04

Matplotlib Version

3.8.0

Matplotlib Backend

module://backend_interagg

Python version

3.9.17, 3.10.12

Jupyter version

N/A

Installation

pip

[ksunden]

This behavior was changed in #26249

I think that the conditional should actually be:

if "color" in kwargs:

as it is using .get really only to determine if it is present or not.

[timhoffm]

I think the condition actually should be

If kwargs.get("color") is not Nonr:

To make explicit color=None work and comply with

c Defaults to None. In that case the marker color is determined by the value of color, facecolor or facecolors. In case those are not specified or None, the marker color is determined by the next color of the Axes' current "shape and fill" color cycle.

from https://matplotlib.org/devdocs/api/_as_gen/matplotlib.axes.Axes.scatter.html#matplotlib.axes.Axes.scatter

[github-actions]

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