René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"hline at y=0 appears after setting yscale to log","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\nCalling `ax.axhline(0)` after setting the y-scale to log rescales the y-axis to make the horizontal line appear at 1e-300.\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug, also minimizing the number of dependencies required--\u003e\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\n\r\nfig, ax = plt.subplots()\r\nax.scatter([1], [1])\r\nax.set_yscale('log')\r\nax.axhline(0)\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![figure_1](https://user-images.githubusercontent.com/6197628/27333637-722e904a-55be-11e7-8104-5007c59920ed.png)\r\nwith the warning\r\n```\r\n/Users/dstansby/matplotlib/lib/matplotlib/axes/_base.py:3208: UserWarning: Attempted to set non-positive ylimits for log-scale axis; invalid limits will be ignored.\r\n  'Attempted to set non-positive ylimits for log-scale axis; '\r\n```\r\n\r\n**Expected outcome**\r\nI would expect the horizontal line to be ignored, and axis limits to remain as they were originally.\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: OSX 10.12.5\r\n  * Matplotlib Version: master branch installed using pip\r\n  * Python Version: 3.6.1\r\n\r\n","author":{"url":"https://github.com/dstansby","@type":"Person","name":"dstansby"},"datePublished":"2017-06-20T12:45:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/8783/matplotlib/issues/8783"}