René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"plt.scatter crashes because overwrites the colors to an empty list","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\nWhen doing scatter plot of `nan` values it crashes because the list of colors gets overwriten to an empty list by this line:\r\n\r\nhttps://github.com/matplotlib/matplotlib/blob/c921e2ead5a9b8ea3dabf74c9aee3958eecfc01e/lib/mpl_toolkits/mplot3d/axes3d.py#L2317\r\n\r\n**Code for reproduction**\r\nWe hit this bug in https://github.com/mne-tools/mne-python/pull/5676, but here is a MWE. Most probably this is a duplicated of #12641. In which case, this can be used as a test.\r\n\r\n```py\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\nn_points = 4\r\nxs = ys = zs = np.full(n_points, np.nan)\r\ncolors = list(np.full(2, 'k'))\r\nplt.scatter(xs, ys, zs, c=colors)\r\nplt.show()\r\n```\r\n\r\n**Expected outcome**\r\n\r\n(As in matplotlib 2.2.2) we would expect an empty plot with no error\r\n```sh\r\nIn [25]: matplotlib.__version__\r\nOut[25]: '2.2.2'\r\n\r\nIn [26]: %paste\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\nn_points = 4\r\nxs = ys = zs = np.full(n_points, np.nan)\r\ncolors = list(np.full(2, 'k'))\r\nplt.scatter(xs, ys, zs, c=colors)\r\nplt.show()\r\n## -- End pasted text --\r\n\r\nIn [27]: \r\n```\r\n\r\n**Actual outcome**\r\nIt breaks because cannot iterate over `c`\r\n\r\n```sh\r\nIn [9]: matplotlib.__version__\r\nOut[9]: '3.0.1'\r\n\r\nIn [10]: %paste\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\nn_points = 4\r\nxs = ys = zs = np.full(n_points, np.nan)\r\ncolors = list(np.full(2, 'k'))\r\nplt.scatter(xs, ys, zs, c=colors)\r\nplt.show()\r\n## -- End pasted text --\r\nTraceback (most recent call last):\r\n  File \"\u003cipython-input-10-f59e87d45c38\u003e\", line 7, in \u003cmodule\u003e\r\n    plt.scatter(xs, ys, zs, c=colors)\r\n  File \"/home/sik/miniconda3/envs/mne/lib/python3.6/site-packages/matplotlib/pyplot.py\", line 2864, in scatter\r\n    is not None else {}), **kwargs)\r\n  File \"/home/sik/miniconda3/envs/mne/lib/python3.6/site-packages/matplotlib/__init__.py\", line 1805, in inner\r\n    return func(ax, *args, **kwargs)\r\n  File \"/home/sik/miniconda3/envs/mne/lib/python3.6/site-packages/matplotlib/axes/_axes.py\", line 4234, in scatter\r\n    .format(nc=n_elem, xs=x.size, ys=y.size)\r\nValueError: 'c' argument has 2 elements, which is not acceptable for use with 'x' with size 4, 'y' with size 4.\r\n```\r\n","author":{"url":"https://github.com/massich","@type":"Person","name":"massich"},"datePublished":"2018-10-29T17:55:06.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/12664/matplotlib/issues/12664"}