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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: FigureCanvasQT is seemingly prematurely freed under certain conditions","articleBody":"### Bug summary\n\nI'm in the process of updating some code using matplotlib and pyside6. Using version 6.6.0 of PySide there is no error, but on versions 6.7.0 and newer I get an error indicating that the underlying C++ object has been prematurely freed. I've had a hard time identifying the source of the bug. I have opened an [issue](https://bugreports.qt.io/browse/PYSIDE-3018) with pyside, but as I have been unable to recreate the bug without matplotlib components I thought I would open an issue here and see if anyone had any ideas. Sorry to bother, and thanks for the help. \n\n\n\n### Code for reproduction\n\n```Python\nfrom PySide6.QtWidgets import QWidget, QMainWindow, QVBoxLayout, QApplication\nfrom matplotlib.backends.backend_qt import FigureCanvasQT\n\nfrom matplotlib.figure import Figure\nclass test_class(QMainWindow):\n    def __init__(self, parent):\n        super().__init__(parent)\n        self.testfig = None\n        self.canvas = FigureCanvasQT(self.testfig)\n        self.vbox = QWidget(self)\n        self.canvas.setParent(self.vbox)\n\ndef test_testing():\n    qtbot = QApplication([])\n    c1 = test_class(None)\n    c1.setVisible(True)\n\ntest_testing()\nQApplication.instance().processEvents()\n```\n\n### Actual outcome\n\nTraceback (most recent call last):\n  File \"/home/ez/test.py\", line 20, in \u003cmodule\u003e\n    QApplication.instance().processEvents()\n  File \"/home/ez/micromamba/envs/pycodas/lib/python3.11/site-packages/matplotlib/backends/backend_qt.py\", line 495, in _draw_idle\n    if self.height() \u003c 0 or self.width() \u003c 0:\n       ^^^^^^^^^^^^^\nRuntimeError: Internal C++ object (FigureCanvasQT) already deleted.\n\n\n### Expected outcome\n\nIt shouldn't do anything, maybe briefly display a window, but the error is unexpected. I may just be using something wrong, but this code did run in the past without error\n\n### Additional information\n\nI should mention that I copied the entire class definition of `FigureCanvasQT` into my test file and that runs just fine, which I find somewhat confusing. Though this may be explained by the fact that I am using version 3.9.1 of matplotlib which may differ from the main branch. \n\n\n### Operating system\n\nubuntu\n\n### Matplotlib Version\n\n3.9.1\n\n### Matplotlib Backend\n\nqtagg\n\n### Python version\n\n3.11.11\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nconda","author":{"url":"https://github.com/ezra-varady","@type":"Person","name":"ezra-varady"},"datePublished":"2025-02-14T03:35:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/29618/matplotlib/issues/29618"}