René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"BUG: matplotlib 3.4.0 -- Scatter with colormap and legend gives TypeError: object of type 'NoneType' has no len()","articleBody":"\u003c!--To help us understand and resolve your issue, please fill out the form to the best of your ability.--\u003e\r\n\u003c!--You can feel free to delete the sections that do not apply.--\u003e\r\n\r\n### Bug report\r\n\r\n**Bug summary**\r\n\r\nWith `matplotlib` 3.4.0, scatter plot with colormap and legend gives `TypeError: object of type 'NoneType' has no len()`.\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug.\r\nPlease make sure to minimize the number of dependencies required, and provide\r\nany necessary plotted data.\r\nAvoid using threads, as Matplotlib is (explicitly) not thread-safe.--\u003e\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\ny = [1, 2, 3, 4, 5]\r\nplt.scatter(y, y, label='Y', lw=0, s=8, c=y, cmap='viridis')\r\nplt.legend()\r\nplt.show()\r\n```\r\n\r\n**Actual outcome**\r\n\r\n\u003c!--The output produced by the above code, which may be a screenshot, console output, etc.--\u003e\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \".../matplotlib/backends/backend_qt5.py\", line 475, in _draw_idle\r\n    self.draw()\r\n  File \".../matplotlib/backends/backend_agg.py\", line 406, in draw\r\n    self.figure.draw(self.renderer)\r\n  File \".../matplotlib/artist.py\", line 74, in draw_wrapper\r\n    result = draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/artist.py\", line 51, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/figure.py\", line 2734, in draw\r\n    mimage._draw_list_compositing_images(\r\n  File \".../matplotlib/image.py\", line 132, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \".../matplotlib/artist.py\", line 51, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/_api/deprecation.py\", line 431, in wrapper\r\n    return func(*inner_args, **inner_kwargs)\r\n  File \".../matplotlib/axes/_base.py\", line 2925, in draw\r\n    mimage._draw_list_compositing_images(renderer, self, artists)\r\n  File \".../matplotlib/image.py\", line 132, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \".../matplotlib/artist.py\", line 51, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/legend.py\", line 614, in draw\r\n    self._legend_box.draw(renderer)\r\n  File \".../matplotlib/offsetbox.py\", line 368, in draw\r\n    c.draw(renderer)\r\n  File \".../matplotlib/offsetbox.py\", line 368, in draw\r\n    c.draw(renderer)\r\n  File \".../matplotlib/offsetbox.py\", line 368, in draw\r\n    c.draw(renderer)\r\n  [Previous line repeated 1 more time]\r\n  File \".../matplotlib/offsetbox.py\", line 694, in draw\r\n    c.draw(renderer)\r\n  File \".../matplotlib/artist.py\", line 51, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/collections.py\", line 1009, in draw\r\n    super().draw(renderer)\r\n  File \".../matplotlib/artist.py\", line 51, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \".../matplotlib/collections.py\", line 380, in draw\r\n    len(facecolors) == 1 and len(edgecolors) == 1 and\r\nTypeError: object of type 'NoneType' has no len()\r\n```\r\n\r\n**Expected outcome**\r\n\r\n\u003c!--A description of the expected outcome from the code snippet--\u003e\r\n\u003c!--If this used to work in an earlier version of Matplotlib, please note the version it used to work on--\u003e\r\n\r\nWith matplotlib 3.3.4, I get this (no warning or error):\r\n\r\n![Screenshot 2021-03-26 141815](https://user-images.githubusercontent.com/2090236/112675923-28e2c980-8e3e-11eb-9954-9eda46cbb6ca.jpg)\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: Red Hat Enterprise Linux Server release 7.9 (Maipo)\r\n  * Matplotlib version (`import matplotlib; print(matplotlib.__version__)`): 3.4.0\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): Qt5Agg\r\n  * Python version: 3.8.3\r\n  * Jupyter version (if applicable): N/A\r\n  * Other libraries: Not sure what else you need, just let me know.\r\n\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\u003c!--If you installed from conda, please specify which channel you used if not the default--\u003e\r\n\r\n","author":{"url":"https://github.com/pllim","@type":"Person","name":"pllim"},"datePublished":"2021-03-26T18:19:04.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/19779/matplotlib/issues/19779"}