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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Existing FigureCanvasQT objects destroyed by call to plt.figure","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nFor a number of years, I have been maintaining an interactive application that embeds subclassed FigureCanvasQT objects within a PyQt application. Up until Matplotlib v3.0.3., it was possible to create standard Matplotlib PyQt figures, i.e., using `plt.figure` within an embedded IPython shell, that coexist with the subclassed canvas objects. Now in Matplotlib v3.1.0, a call to `plt.figure()` destroys all the other canvas objects. \r\n\r\nUnfortunately, I cannot debug this within Visual Studio since I am currently unable to install Matplotlib from the source. By going through the `new_figure_manager` code line by line, I can confirm that the windows are destroyed when calling `FigureCanvasQT.__init__(figure)`, but not when calling `FigureCanvasBase.__init__(figure)`, but I can't work out what triggers the destruction of the other windows. I presume the subclassed canvasses are not being registered somewhere, and `pyplot` assumes they are no longer active, but I am hoping someone will show me where to look. This may not be a Matplotlib bug, but it's certainly an unwelcome side effect in my application.\r\n\r\n**Code for reproduction**\r\nIf you have `nexpy` installed (`pip install nexpy`) and launch it, you can reproduce this from within the embedded IPython shell with the following, which creates a new subclassed window and then attempts to open a regular `pyplot` window.:\r\n\r\n```\r\nIn [1]: new_window=NXPlotView()\r\nIn [2]: plt.get_fignums()\r\nOut[2]: [1, 2]\r\nIn [3]: plt.figure()\r\n```\r\nThere are two figure numbers, because NeXpy automatically creates a window with a figure number of 1 when it is launched.\r\n\r\n**Actual outcome**\r\n\r\nA new window with an updated figure number is created but all other windows not created by `pyplot`  are destroyed.\r\n\r\n```\r\nIn [4]: plt.get_fignums()\r\nOut[4]: [3]\r\n```\r\n\r\n**Expected outcome**\r\n\r\nIn Matplotlib v3.0.3, a new `pyplot` window is created by the PyQt5 backend without destroying anything else.\r\n\r\n```\r\nIn [4]: plt.get_fignums()\r\nOut[4]: [1, 2, 3]\r\n```\r\n\r\n**Matplotlib version**\r\n  * Operating system: Mac OS v10.14.5\r\n  * Matplotlib version: 3.1.0\r\n  * Matplotlib backend: Qt5Agg\r\n  * Python version: 3.7.2\r\n  * Jupyter version (if applicable): 1.0.0\r\n  * Other libraries: \r\n\r\n\u003c!--Please tell us how you installed matplotlib and python e.g., from source, pip, conda--\u003e\r\n\u003c!--If you installed from conda, please specify which channel you used if not the default--\u003e\r\n","author":{"url":"https://github.com/rayosborn","@type":"Person","name":"rayosborn"},"datePublished":"2019-06-02T21:12:25.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":23},"url":"https://github.com/14426/matplotlib/issues/14426"}