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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: pyplot.subplot_tool doesn't always return a SubplotTool","articleBody":"### Bug summary\n\nPer the [matplotlib.pyplot.subplot_tool documentation](https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.subplot_tool.html#matplotlib.pyplot.subplot_tool), the return value is suppose to be a `matplotlib.widgets.SubplotTool` instance.\n\nIn pyplot.py, the type hint also specifies that None can be returned:\n\n```python\ndef subplot_tool(targetfig: Figure | None = None) -\u003e SubplotTool | None:\n    \"\"\"\n    Launch a subplot tool window for a figure.\n\n    Returns\n    -------\n    `matplotlib.widgets.SubplotTool`\n    \"\"\"\n```\n\nHowever, when using the qtagg backend, a `SubplotToolQt` instance is returned. Despite the name, it doesn't inherit from `SubplotTool`, only `QtWidgets.QDialog`.\n\nI think there are multiple issues here:\n\n1. The documentation should mention the None case\n2. `configure_subplot` in `backend_bases.pyi` should have a type hint with a return value of `widgets.SubplotTool | None`.\n3. qtagg should then return `None` from its configure_subplot method.\n\nAlternatively, `SubplotToolQt` should inherit from both `SubplotTool` and `QtWidgets.QDialog`, but I'm not sure what all that would entail.\n\n### Code for reproduction\n\n```Python\nimport matplotlib.pyplot as plt\nimport matplotlib\nimport numpy as np\n\nx = np.linspace(0, 10, 100)\nfig, ax = plt.subplots()\nax.plot(x, np.sin(x))\n\ntool = plt.subplot_tool()\nif tool:\n    assert isinstance(tool, matplotlib.widgets.SubplotTool)\n\nplt.show()\n```\n\n### Actual outcome\n\nAssertionError\n\n### Expected outcome\n\nNo assertion.\n\n### Additional information\n\n_No response_\n\n### Operating system\n\n_No response_\n\n### Matplotlib Version\n\n3.11\n\n### Matplotlib Backend\n\nqtagg\n\n### Python version\n\n3.14.5\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nNone","author":{"url":"https://github.com/iccir","@type":"Person","name":"iccir"},"datePublished":"2026-07-02T02:52:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/31979/matplotlib/issues/31979"}