René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: Backend falls back to Agg even though TkAgg will work","articleBody":"### Bug summary\n\nI've set MPLBACKEND to be \"TkAgg\". When I import `matplotlib.pyplot`, the backend switches to \"agg\". I'm assuming this is some fallback behavior, which would be understandable except for the fact that TkAgg works just fine\n\nIf I manually set backend with `matplotlib.use(\"TkAgg\")` before importing pyplot, things work as expected. \n\nI would like to avoid having to set the backend in python code, since I might use this with other backends as well\n\n### Code for reproduction\n\n```Python\n# test1.py\nimport matplotlib\nmatplotlib.use(\"TkAgg\")\nimport matplotlib.pyplot as plt\nassert plt.get_backend() == \"TkAgg\"  # This works. Plotting also uses Tk as expected\n\n# test2.py\nimport matplotlib.pyplot as plt\nassert plt.get_backend() == \"TkAgg\"  # AssertError. Got \"agg\" instead\n```\n\n### Actual outcome\n\nNo output for `test1.py`\n\nAssertionError for `test2.py`\n\n### Expected outcome\n\nNo output for either\n\n### Additional information\n\nOutput with DEBUG level logging, in case that might prove useful\n\n```\nDEBUG:matplotlib:matplotlib data path: xxxxxREDACTEDxxxxx/.venv/lib/python3.13/site-packages/matplotlib/mpl-data\nDEBUG:matplotlib:CONFIGDIR=xxxxxREDACTEDxxxxx\nDEBUG:matplotlib:interactive is False\nDEBUG:matplotlib:platform is linux\nDEBUG:matplotlib:CACHEDIR=xxxxxREDACTEDxxxxx\nDEBUG:matplotlib.font_manager:Using fontManager instance from xxxxxREDACTEDxxxxx/fontlist-v390.json\nDEBUG:matplotlib.pyplot:Loaded backend agg version v2.2.\n```\n\n### Operating system\n\nNixOS\n\n### Matplotlib Version\n\n3.10.9\n\n### Matplotlib Backend\n\nTkAgg\n\n### Python version\n\n3.13.12\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nuv","author":{"url":"https://github.com/parthkalgaonkar","@type":"Person","name":"parthkalgaonkar"},"datePublished":"2026-05-20T03:30:45.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/31715/matplotlib/issues/31715"}