René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Matplotlib \u003e= v3.3.3 breaks with pandas.plotting.register_matplotlib_converters(), ax.pcolormesh(), and datetime objects","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nMatplotlib \u003e= v3.3.3 breaks when using `pandas.plotting.register_matplotlib_converters()`, `ax.pcolormesh()`, and and array of `datetime.datetime()` objects as coordinates.\r\n\r\nCode was tested using clean conda environments only differing by Matplotlib version. Versions tested:\r\n\r\n- mpl v3.3.2: Code works\r\n- mpl v3.3.3: Code breaks\r\n- mpl v3.4.1: Code breaks\r\n\r\n**Code for reproduction**\r\nThe code below will work if the following lines are commented/removed:\r\n```\r\nfrom pandas.plotting import register_matplotlib_converters\r\nregister_matplotlib_converters()\r\n```\r\n\r\n```\r\n#!/usr/bin/env python3\r\nfrom matplotlib import pyplot as plt\r\nimport numpy as np\r\nimport datetime\r\n\r\nfrom pandas.plotting import register_matplotlib_converters\r\nregister_matplotlib_converters()\r\n\r\nfig = plt.figure()\r\nax  = fig.add_subplot(111)\r\n\r\ntimes   = [datetime.datetime(2021,1,1)]\r\nwhile len(times) \u003c 721:\r\n    times.append(times[-1]+datetime.timedelta(seconds=120))\r\n\r\ny_vals  = np.arange(101)\r\n\r\ntime_axis, y_axis   = np.meshgrid(times,y_vals)\r\nshape               = (len(y_vals)-1,len(times)-1)\r\nz_data              = np.arange(shape[0]*shape[1])\r\nz_data.shape        = shape\r\n\r\nim = ax.pcolormesh(time_axis, y_axis, z_data)\r\nfig.savefig('bug_report.png')\r\n```\r\n\r\n**Actual outcome**\r\n\r\nThis traceback comes from my Matplotlib 3.4.1 conda environment:\r\n```\r\nTraceback (most recent call last):\r\n  File \"./bug_report.py\", line 23, in \u003cmodule\u003e\r\n    im = ax.pcolormesh(time_axis, y_axis, z_data)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.4.1/lib/python3.7/site-packages/matplotlib/__init__.py\", line 1352, in inner\r\n    return func(ax, *map(sanitize_sequence, args), **kwargs)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.4.1/lib/python3.7/site-packages/matplotlib/axes/_axes.py\", line 6163, in pcolormesh\r\n    shading=shading, kwargs=kwargs)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.4.1/lib/python3.7/site-packages/matplotlib/axes/_axes.py\", line 5655, in _pcolorargs\r\n    Nx = X.shape[-1]\r\nAttributeError: 'list' object has no attribute 'shape'\r\n```\r\nThis traceback comes from my Matplotlib 3.3.3 conda environment:\r\n```\r\nTraceback (most recent call last):\r\n  File \"./bug_report.py\", line 23, in \u003cmodule\u003e\r\n    im = ax.pcolormesh(time_axis, y_axis, z_data)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.3.3/lib/python3.7/site-packages/matplotlib/__init__.py\", line 1447, in inner\r\n    return func(ax, *map(sanitize_sequence, args), **kwargs)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.3.3/lib/python3.7/site-packages/matplotlib/axes/_axes.py\", line 6093, in pcolormesh\r\n    shading=shading, kwargs=kwargs)\r\n  File \"/home/w2naf/anaconda3/envs/mpl3.3.3/lib/python3.7/site-packages/matplotlib/axes/_axes.py\", line 5590, in _pcolorargs\r\n    Nx = X.shape[-1]\r\nAttributeError: 'list' object has no attribute 'shape'\r\n```\r\n\r\n**Expected outcome**\r\nOutput from my Matplotlib 3.3.2 conda environment:\r\n![bug_report](https://user-images.githubusercontent.com/1831182/113606904-9a78ff80-9616-11eb-9dab-fdf8f093681c.png)\r\n\r\n**Matplotlib version**\r\n\u003c!--Please specify your platform and versions of the relevant libraries you are using:--\u003e\r\n  * Operating system: Ubuntu 18.04.5 LTS\r\n  * Matplotlib version: Code breaks in v3.3.3 and v3.4.1; Code works in v3.3.2\r\n  * Matplotlib backend: Qt5Agg\r\n  * Python version: 3.7.7\r\n  * Other libraries: Pandas v1.2.3\r\n\r\nMatplotlib and python were installed with Anaconda for Linux 64 Bit. (conda 4.9.2)\r\n\r\n","author":{"url":"https://github.com/w2naf","@type":"Person","name":"w2naf"},"datePublished":"2021-04-05T18:02:15.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/19871/matplotlib/issues/19871"}