René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"UserWarning thrown when all values are \"bad\", but not when only some are","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\nIf all values passed as colors are \"bad\" (`np.nan`), a warning is thrown from numpy about converting masked values to null. If some of the values are \"bad\", this does not happen.\r\n\r\n**Code for reproduction**\r\n\r\n```python\r\nimport numpy as np, matplotlib.pyplot as plt\r\n```\r\n\r\nThis does not warn:\r\n\r\n```python\r\nc = np.full(10, np.nan)\r\nc[0] = 1.\r\nplt.scatter(np.ones(10), np.ones(10), c=c)\r\nplt.show()\r\n```\r\n\r\nThis does:\r\n\r\n```python\r\nplt.scatter(np.ones(10), np.ones(10), c=np.full(10, np.nan))\r\nplt.show()\r\n```\r\n\r\n```pytb\r\n\u003c__array_function__ internals\u003e:5: UserWarning: Warning: converting a masked element to nan.\r\n/usr/local/lib/python3.8/site-packages/numpy/core/_asarray.py:85: UserWarning: Warning: converting a masked element to nan.\r\n  return array(a, dtype, copy=False, order=order)\r\n```\r\n\r\nThis is difficult to hide since since the warning is not thrown when the figure is being constructed, but when it is shown. Here's a full traceback to show this:\r\n\r\n\u003cdetails\u003e\r\n\u003csummary\u003e Full traceback \u003c/summary\u003e\r\n\r\n```pytb\r\n  File \"\u003cstdin\u003e\", line 1, in \u003cmodule\u003e\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/pyplot.py\", line 337, in show\r\n    return _backend_mod.show(*args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backend_bases.py\", line 3544, in show\r\n    cls.mainloop()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backends/backend_macosx.py\", line 171, in mainloop\r\n    _macosx.show()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backends/backend_macosx.py\", line 61, in _draw\r\n    self.figure.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/figure.py\", line 1863, in draw\r\n    mimage._draw_list_compositing_images(\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/image.py\", line 131, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/cbook/deprecation.py\", line 411, in wrapper\r\n    return func(*inner_args, **inner_kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/axes/_base.py\", line 2748, in draw\r\n    mimage._draw_list_compositing_images(renderer, self, artists)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/image.py\", line 131, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 931, in draw\r\n    Collection.draw(self, renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 346, in draw\r\n    self.update_scalarmappable()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 855, in update_scalarmappable\r\n    self._facecolors = self.to_rgba(self._A, self._alpha)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/cm.py\", line 332, in to_rgba\r\n    x = self.norm(x)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/colors.py\", line 1048, in __call__\r\n    (vmin,), _ = self.process_value(self.vmin)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/colors.py\", line 1012, in process_value\r\n    dtype = np.min_scalar_type(value)\r\n  File \"\u003c__array_function__ internals\u003e\", line 5, in min_scalar_type\r\n  File \"/usr/local/lib/python3.8/site-packages/numpy/ma/core.py\", line 4331, in __float__\r\n    warnings.warn(\"Warning: converting a masked element to nan.\", stacklevel=2)\r\n  File \"/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/warnings.py\", line 109, in _showwarnmsg\r\n    sw(msg.message, msg.category, msg.filename, msg.lineno,\r\n  File \"\u003cstdin\u003e\", line 3, in warn_with_traceback\r\n\u003c__array_function__ internals\u003e:5: UserWarning: Warning: converting a masked element to nan.\r\n  File \"\u003cstdin\u003e\", line 1, in \u003cmodule\u003e\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/pyplot.py\", line 337, in show\r\n    return _backend_mod.show(*args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backend_bases.py\", line 3544, in show\r\n    cls.mainloop()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backends/backend_macosx.py\", line 171, in mainloop\r\n    _macosx.show()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/backends/backend_macosx.py\", line 61, in _draw\r\n    self.figure.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/figure.py\", line 1863, in draw\r\n    mimage._draw_list_compositing_images(\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/image.py\", line 131, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/cbook/deprecation.py\", line 411, in wrapper\r\n    return func(*inner_args, **inner_kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/axes/_base.py\", line 2748, in draw\r\n    mimage._draw_list_compositing_images(renderer, self, artists)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/image.py\", line 131, in _draw_list_compositing_images\r\n    a.draw(renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 931, in draw\r\n    Collection.draw(self, renderer)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/artist.py\", line 41, in draw_wrapper\r\n    return draw(artist, renderer, *args, **kwargs)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 346, in draw\r\n    self.update_scalarmappable()\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/collections.py\", line 855, in update_scalarmappable\r\n    self._facecolors = self.to_rgba(self._A, self._alpha)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/cm.py\", line 332, in to_rgba\r\n    x = self.norm(x)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/colors.py\", line 1048, in __call__\r\n    (vmin,), _ = self.process_value(self.vmin)\r\n  File \"/usr/local/lib/python3.8/site-packages/matplotlib/colors.py\", line 1019, in process_value\r\n    data = np.asarray(value)\r\n  File \"/usr/local/lib/python3.8/site-packages/numpy/core/_asarray.py\", line 85, in asarray\r\n    return array(a, dtype, copy=False, order=order)\r\n  File \"/usr/local/lib/python3.8/site-packages/numpy/ma/core.py\", line 4331, in __float__\r\n    warnings.warn(\"Warning: converting a masked element to nan.\", stacklevel=2)\r\n  File \"/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/warnings.py\", line 109, in _showwarnmsg\r\n    sw(msg.message, msg.category, msg.filename, msg.lineno,\r\n  File \"\u003cstdin\u003e\", line 3, in warn_with_traceback\r\n/usr/local/lib/python3.8/site-packages/numpy/core/_asarray.py:85: UserWarning: Warning: converting a masked element to nan.\r\n  return array(a, dtype, copy=False, order=order)\r\n```\r\n\r\n\u003c/details\u003e\r\n\r\n**Expected outcome**\r\n\r\nI wouldn't expect the second to warn if the first doesn't.\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: macOS\r\n  * Matplotlib version: 3.3.1\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): MacOSX and module://ipykernel.pylab.backend_inline\r\n  * Python version: 3.8.5\r\n  * Jupyter version (if applicable): Replicates in python repl, but also was happening in ipython and jupyter lab\r\n  * Other libraries: \r\n\r\nInstalled with pip","author":{"url":"https://github.com/ivirshup","@type":"Person","name":"ivirshup"},"datePublished":"2020-08-19T06:07:26.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/18294/matplotlib/issues/18294"}