René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: plt.bar legend displays incorrect style for empty data","articleBody":"### Bug summary\r\n\r\nLegend items created from empty `plt/ax.bar` calls are displayed with the default style and the first color of the theme's cycle. This behavior contradicts the behavior of `plt/ax.plot` and `plt/ax.scatter`.\r\n\r\n### Code for reproduction\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\n# The bug happens with or without this import.\r\nimport numpy as np\r\n```\r\n\r\n```python\r\n# Actual outcome code\r\nplt.bar([], [], alpha=0.3, label=\"[], [], alpha=0.3\")\r\nplt.bar([], [], alpha=0.3, label=\"[], [], alpha=0.3\")\r\nplt.bar([np.nan], [np.nan], alpha=0.3, label=\"[np.nan], [np.nan], alpha=0.3\")\r\nplt.bar([], [], alpha=0.3, label=\"[], [], alpha=0.3\")\r\nplt.bar([1], [1], alpha=0.3, label=\"[1], [1], alpha=0.3\")\r\nplt.legend()\r\n```\r\n\r\n\r\n```python\r\n# Expected outcome code\r\nplt.plot([], [], alpha=0.5, label=\"[], [], alpha=0.5\")\r\nplt.plot([], [], alpha=0.5, label=\"[], [], alpha=0.5\")\r\nplt.plot([np.nan], [np.nan], alpha=0.5, label=\"[np.nan], [np.nan], alpha=0.5\")\r\nplt.plot([], [], alpha=0.5, label=\"[], [], alpha=0.5\")\r\nplt.plot([1], [1], alpha=0.5, label=\"[1], [1], alpha=0.5\")\r\nplt.legend()\r\n```\r\n\r\n### Actual outcome\r\n\r\nColor cycling and alpha are not respected for the `plt.bar([], [], ...)` calls.\r\n\r\n![image](https://user-images.githubusercontent.com/40036383/139554362-96079ce0-ab4a-4aea-9907-b4ad790b562d.png)\r\n\r\n\r\n### Expected outcome\r\n\r\nColor cycling and alpha are respected for the `plt.plot([], [], ...)` calls.\r\n\r\n![image](https://user-images.githubusercontent.com/40036383/139554641-e2371ab6-fae6-484c-8d50-91e1f2825adb.png)\r\n\r\n\r\n### Operating system\r\n\r\nLinux\r\n\r\n### Matplotlib Version\r\n\r\n3.2.2\r\n\r\n### Matplotlib Backend\r\n\r\nmodule://ipykernel.pylab.backend_inline\r\n\r\n### Python version\r\n\r\n3.7.12 (default, Sep 10 2021, 00:21:48)  [GCC 7.5.0]\r\n\r\n### Jupyter version\r\n\r\nColab\r\n\r\n### Other libraries\r\n\r\n_No response_\r\n\r\n### Installation\r\n\r\n_No response_\r\n\r\n### Conda channel\r\n\r\n_No response_","author":{"url":"https://github.com/phoenix-meadowlark","@type":"Person","name":"phoenix-meadowlark"},"datePublished":"2021-10-30T18:36:50.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/21506/matplotlib/issues/21506"}