René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: regression with ScalarMappable and `.set_array` and `autoscale_None`","articleBody":"### Bug summary\r\n\r\nWe are creating manual `ScalarMappable` instances in some cases where colorbar creation is detached from the plotting event.  Changed in #20511 an element-wise comparison of the color array is made, however, with `ScalarMappable.set_array` there appears to be no assurances that the `._A` attribute will support such comparison.\r\n\r\n### Code for reproduction\r\n\r\n```python\r\nimport matplotlib as mpl\r\nimport matplotlib.pyplot as plt\r\nnorm = mpl.colors.LogNorm()\r\ncmap = mpl.cm.get_cmap(\"viridis\")\r\nfig, ax = plt.subplots()\r\npts = mpl.cm.ScalarMappable(norm=norm, cmap=cmap)\r\npts.set_array([0.1, 0.9])\r\nplt.colorbar(pts)\r\n```\r\n\r\n\r\n### Actual outcome\r\n\r\n```\r\n---------------------------------------------------------------------------\r\nTypeError                                 Traceback (most recent call last)\r\n\u003cipython-input-1-adec5b1bbfd1\u003e in \u003cmodule\u003e\r\n      6 pts = mpl.cm.ScalarMappable(norm=norm, cmap=cmap)\r\n      7 pts.set_array([0.1, 0.9])\r\n----\u003e 8 plt.colorbar(pts)\r\n\r\n~/rms-python/envs/mpl34/lib/python3.7/site-packages/matplotlib/pyplot.py in colorbar(mappable, cax, ax, **kw)\r\n   2354                                'an image (with imshow) or a contour set ('\r\n   2355                                'with contourf).')\r\n-\u003e 2356     ret = gcf().colorbar(mappable, cax=cax, ax=ax, **kw)\r\n   2357     return ret\r\n   2358\r\n\r\n~/rms-python/envs/mpl34/lib/python3.7/site-packages/matplotlib/figure.py in colorbar(self, mappable, cax, ax, use_gridspec, **kw)\r\n   1174                              'panchor']\r\n   1175         cb_kw = {k: v for k, v in kw.items() if k not in NON_COLORBAR_KEYS}\r\n-\u003e 1176         cb = cbar.Colorbar(cax, mappable, **cb_kw)\r\n   1177\r\n   1178         self.sca(current_ax)\r\n\r\n~/rms-python/envs/mpl34/lib/python3.7/site-packages/matplotlib/colorbar.py in __init__(self, ax, mappable, **kwargs)\r\n   1170         # even if mappable.draw has not yet been called.\r\n   1171         if mappable.get_array() is not None:\r\n-\u003e 1172             mappable.autoscale_None()\r\n   1173\r\n   1174         self.mappable = mappable\r\n\r\n~/rms-python/envs/mpl34/lib/python3.7/site-packages/matplotlib/cm.py in autoscale_None(self)\r\n    474         if self._A is None:\r\n    475             raise TypeError('You must first set_array for mappable')\r\n--\u003e 476         self.norm.autoscale_None(self._A)\r\n    477         self.changed()\r\n    478\r\n\r\n~/rms-python/envs/mpl34/lib/python3.7/site-packages/matplotlib/colors.py in autoscale_None(self, A)\r\n   1541     def autoscale_None(self, A):\r\n   1542         # docstring inherited.\r\n-\u003e 1543         super().autoscale_None(np.ma.array(A, mask=(A \u003c= 0)))\r\n   1544\r\n   1545\r\n\r\nTypeError: '\u003c=' not supported between instances of 'list' and 'int'\r\n```\r\n\r\n### Expected outcome\r\n\r\nNo error.\r\n\r\n### Operating system\r\n\r\nUbuntu\r\n\r\n### Matplotlib Version\r\n\r\n3.4.3\r\n\r\n### Matplotlib Backend\r\n\r\nagg\r\n\r\n### Python version\r\n\r\n3.7.10\r\n\r\n### Jupyter version\r\n\r\nNA\r\n\r\n### Other libraries\r\n\r\nnumpy 1.18.5\r\n\r\n### Installation\r\n\r\nconda\r\n\r\n### Conda channel\r\n\r\nconda-forge","author":{"url":"https://github.com/ryandvmartin","@type":"Person","name":"ryandvmartin"},"datePublished":"2021-08-25T18:53:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/20902/matplotlib/issues/20902"}