René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Aspect ratio for not so common scales","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\nBringing up [this stackoverflow question](https://stackoverflow.com/questions/55438189/matplotlib-symlog-plot-with-non-auto-aspect-ratio) on the issue tracker.\r\n\r\nSetting an equal aspect for symlog scales results in an `UnboundLocalError`. This should never happen, independent on how meaningful the notion of \"aspect\" would be such case.\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```\r\nimport matplotlib.pyplot as plt\r\nimport numpy as np\r\n\r\ndt = 0.01\r\nx = np.arange(-50.0, 50.0, dt)\r\ny = np.arange(0, 100.0, dt)\r\n\r\nfig = plt.figure()\r\nax = fig.add_subplot(111,aspect='equal')\r\n\r\nplt.plot(x, np.sin(x / 3.0))\r\nplt.xscale('symlog')\r\nplt.yscale('symlog', linthreshy=0.015)\r\nplt.grid(True)\r\nplt.ylabel('symlog both')\r\n\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\nUnboundLocalError: local variable 'aspect_scale_mode' referenced before assignment\r\n```\r\n\r\n**Expected outcome**\r\n\r\nEither of the following:\r\n\r\n* An error telling that symlog does not support equal aspect.\r\n* A warning of the above and a fallback to `aspect=\"auto\".\r\n* A meaningful plot, in case someone has an idea of what \"aspect\" could mean in the case of two symlog scales.\r\n\r\n**Analysis**\r\n\r\nThe problem comes from https://github.com/matplotlib/matplotlib/blob/699f35e4d8d424393a7038428abc573d591bd6db/lib/matplotlib/axes/_base.py#L1469-L1485\r\n\r\nwhere there are a lot of cases for which the variable `aspect_scale_mode` isn't defined. I.e. each case that ends up in the `pass` section.\r\nWhen later accessing `aspect_scale_mode` in \r\nhttps://github.com/matplotlib/matplotlib/blob/699f35e4d8d424393a7038428abc573d591bd6db/lib/matplotlib/axes/_base.py#L1502-L1505\r\n\r\nthe above error is raised. \r\n\r\nThis brings up a more general question: Wouldn't the axis and its `Scale` actually need to be asked about their data limits? Something like (in pseudo code)\r\n\r\n    box_aspect = A * (tranformed(self.yaxis.bounds[1]) -  tranformed(self.yaxis.bounds[1]))/\r\n                        (tranformed(self.xaxis.bounds[0]) -  tranformed(self.xaxis.bounds[0]))\r\n\r\nsuch that other / custom scales can have an aspect defined?\r\n\r\nRelated issue: https://github.com/matplotlib/matplotlib/issues/8878\r\n\r\n**Matplotlib version**\r\n\r\n  * Matplotlib version: master\r\n","author":{"url":"https://github.com/ImportanceOfBeingErnest","@type":"Person","name":"ImportanceOfBeingErnest"},"datePublished":"2019-03-31T15:43:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/13819/matplotlib/issues/13819"}