René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"In 3.0.0 backend cannot be set if 'get_backend()' is run first","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\nIn my code, I need to check whether the matplotlib backend has already been set.  If it has not been set, I need to then set it to 'WXAgg'.  In matplotlib 2.*, I was able to do this, but in matplotlib 3.0.0 it fails.\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\r\nif not matplotlib.get_backend() == 'WXAgg':\r\n    matplotlib.use('WXAgg')\r\nprint('backend:', matplotlib.get_backend())\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\nWith matplotlib 3.0.0:\r\n```\r\n/Users/nebula/Python/PmagPy/programs/test.py:7: UserWarning: matplotlib.pyplot as already been /Users/nebula/Python/PmagPy/programs/test.py:7: UserWarning: matplotlib.pyplot as already been imported, this call will have no effect.\r\n  matplotlib.use('WXAgg')\r\nbackend: MacOSX\r\n```\r\n\r\n**Expected outcome**\r\n\r\nWith matplotlib 2.2.3:\r\n```\r\nbackend: WXAgg\r\n```\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 High Sierra 10.13.6\r\n  * Matplotlib version: 3.0.0\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`):\r\n  * Python version: 3.6.6 (Anaconda, default channel)\r\n  * Jupyter version (if applicable):\r\n  * Other libraries: \r\n\r\n\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\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/moonshoes87","@type":"Person","name":"moonshoes87"},"datePublished":"2018-10-01T20:14:39.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":16},"url":"https://github.com/12362/matplotlib/issues/12362"}