René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Cannot create custom colorbar with SymLogNorm","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\nCreating a colorbar with a `SymLogNorm` fails, using the `fig.colorbar(cm.ScalarMappable(norm=norm, cmap=cmap), ax=ax)` example given in the docs.\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\nimport matplotlib.colors as mcolor\r\nimport matplotlib.cm as cm\r\n\r\nnorm = mcolor.SymLogNorm(5)\r\n\r\nfig, ax = plt.subplots()\r\nfig.colorbar(cm.ScalarMappable(norm=norm, cmap='viridis'), cax=ax)\r\n\r\n```\r\n\r\n**Actual outcome**\r\n\r\n```python\r\nTraceback (most recent call last):\r\n  File \"test.py\", line 8, in \u003cmodule\u003e\r\n    fig.colorbar(cm.ScalarMappable(norm=norm, cmap='viridis'), cax=ax)\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/figure.py\", line 2201, in colorbar\r\n    cb = cbar.colorbar_factory(cax, mappable, **cb_kw)\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colorbar.py\", line 1686, in colorbar_factory\r\n    cb = Colorbar(cax, mappable, **kwargs)\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colorbar.py\", line 1210, in __init__\r\n    ColorbarBase.__init__(self, ax, **kwargs)\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colorbar.py\", line 472, in __init__\r\n    self.draw_all()\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colorbar.py\", line 495, in draw_all\r\n    self._process_values()\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colorbar.py\", line 945, in _process_values\r\n    b = self.norm.inverse(self._uniform_y(self.cmap.N + 1))\r\n  File \"/Users/dstansby/github/matplotlib/lib/matplotlib/colors.py\", line 1276, in inverse\r\n    val = val * (self._upper - self._lower) + self._lower\r\nAttributeError: 'SymLogNorm' object has no attribute '_upper'\r\n```\r\n\r\n**Expected outcome**\r\n\r\nNo error\r\n\r\n**Matplotlib version**\r\n  * Operating system: macOS 10.15.2\r\n  * Matplotlib version: '3.2.0rc2.post1221+g20805b805'\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): Qt5Agg\r\n  * Python version: 3.7\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: \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/dstansby","@type":"Person","name":"dstansby"},"datePublished":"2020-01-20T16:21:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/16269/matplotlib/issues/16269"}