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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Incorrect behaviour: plt.show(block=True) with qt5 and jupyter","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\nI'm implementing live plotting for our data acquisition system using Jupyter and FuncAnimation, and have just found an interesting defect in `plt.show(block=True)` behaviour.\r\n\r\nPrecisely, it does not unblock when the plot window is closed, and sending KeyboardInterrupt crashes the kernel.\r\n\r\nI was able to accidentally fix the first part by modifying the `show()` function in `backend_bases.py` based on [this](https://www.qtcentre.org/threads/62183-QDialog-show()-exec()-and-blocking) forum reply (basically, by not calling `manager.canvas.figure.show()` when block is not None, and instead calling`manager.window.setVisible(True)` just before `cls.mainloop()` since it calls Qt's `exec()` that should call `show()` by itself)\r\n\r\nThe second issue persists, though.\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug.\r\nPlease make sure to minimize the number of dependencies required, and provide\r\nany necessary plotted data.\r\nAvoid using threads, as Matplotlib is (explicitly) not thread-safe.--\u003e\r\n\r\n```python\r\n%pylab qt5\r\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\nfrom matplotlib.animation import FuncAnimation\r\nfig, ax = plt.subplots()\r\nxdata, ydata = [], []\r\nln, = plt.plot([], [], 'ro')\r\n\r\ndef init():\r\n    ax.set_xlim(0, 2*np.pi)\r\n    ax.set_ylim(-1, 1)\r\n    return ln,\r\n\r\ndef update(frame):\r\n    xdata.append(frame)\r\n    ydata.append(np.sin(frame))\r\n    ln.set_data(xdata, ydata)\r\n    return ln,\r\n\r\nani = FuncAnimation(fig, update, frames=np.linspace(0, 2*np.pi, 128),\r\n                    init_func=init, blit=True, interval = 50)\r\n\r\nplt.show(block=True)\r\n```\r\n\r\n**Actual outcome**\r\n\r\nPlot window that can be closed by either pressing the corresponding window button or by sending KeyboardInterrupt. The kernel then should be freed.\r\n\r\n**Expected outcome**\r\n\r\nThe kernel is not freed upon closing (without my fix) and dies on KeyboardInterrupt.\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: 4.18.16-100.fc27.x86_64\r\n  * Matplotlib version: 3.0.2\r\n  * Matplotlib backend: Qt5Agg\r\n  * Python version: 3.6\r\n  * IPython: 7.2.0\r\n  * Jupyter notebook: 5.7.4\r\n\r\nEverything installed with pip in a virtualenv.\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\r\n","author":{"url":"https://github.com/vdrhtc","@type":"Person","name":"vdrhtc"},"datePublished":"2019-01-27T21:28:22.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":22},"url":"https://github.com/13302/matplotlib/issues/13302"}