René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Animation freezes in Jupyter notebook","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\nA `FuncAnimation` in a Jupyter notebook runs through once but freezes when it should repeat.\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%matplotlib notebook\r\nimport matplotlib as mpl\r\nfrom matplotlib import pyplot as plt\r\nimport numpy as np\r\n\r\nfig = plt.figure()\r\nnt = 25\r\n\r\nt = np.linspace(0,1,nt)\r\nf = np.sin(2.*np.pi*t)\r\n\r\nax = plt.axes(xlim=[0,1],ylim=[-1,1])\r\nline = ax.plot(t[:1], f[:1])[0]\r\n\r\ndef update_func(i):\r\n    line.set_xdata(t[:i])\r\n    line.set_ydata(f[:i])\r\n    \r\nanim = mpl.animation.FuncAnimation(fig, update_func, nt, repeat=True)\r\n```\r\n\r\nPassing `repeat_delay=1` to `FuncAnimation` on the last line prevents the error. It looks like having `repeat_delay=0` sets `TimerTornado.interval` to `0`, but `tornado.ioloop.PeriodicCallback` requires a *positive* value for `interval`.\r\n\r\n**Actual outcome**\r\n\r\n\u003c!--The output produced by the above code, which may be a screenshot, console output, etc.--\u003e\r\n\r\nThis error appears in the console when the animation crashes.\r\n```\r\nERROR:tornado.application:Exception in callback \u003cbound method TimerBase._on_timer of \u003cmatplotlib.backends.backend_webagg_core.TimerTornado object at 0x7f8627585610\u003e\u003e\r\nTraceback (most recent call last):\r\n  File \".../site-packages/tornado/ioloop.py\", line 907, in _run\r\n    return self.callback()\r\n  File \".../site-packages/matplotlib/backend_bases.py\", line 1194, in _on_timer\r\n    ret = func(*args, **kwargs)\r\n  File \".../site-packages/matplotlib/animation.py\", line 1432, in _step\r\n    self.event_source.interval = self._repeat_delay\r\n  File \".../site-packages/matplotlib/backend_bases.py\", line 1135, in interval\r\n    self._timer_set_interval()\r\n  File \".../site-packages/matplotlib/backends/backend_webagg_core.py\", line 537, in _timer_set_interval\r\n    self._timer_start()\r\n  File \".../site-packages/matplotlib/backends/backend_webagg_core.py\", line 518, in _timer_start\r\n    self._timer = tornado.ioloop.PeriodicCallback(\r\n  File \".../site-packages/tornado/ioloop.py\", line 873, in __init__\r\n    raise ValueError(\"Periodic callback must have a positive callback_time\")\r\nValueError: Periodic callback must have a positive callback_time\r\n\r\n```\r\n\r\n**Expected outcome**\r\n\r\n\u003c!--A description of the expected outcome from the code snippet--\u003e\r\n\u003c!--If this used to work in an earlier version of Matplotlib, please note the version it used to work on--\u003e\r\nThe animation plays continuously.\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: Linux Mint 19\r\n  * Matplotlib version: 3.3.2\r\n  * Matplotlib backend (`print(matplotlib.get_backend())`): nbAgg\r\n  * Python version: 3.8.5\r\n  * Jupyter version (if applicable): 6.1.4\r\n  * Other libraries: \r\n      * IPython: 7.18.1\r\n      * tornado: 6.0.4\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\nInstalled all packages from conda, using conda-forge","author":{"url":"https://github.com/johnomotani","@type":"Person","name":"johnomotani"},"datePublished":"2020-09-25T22:18:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/18580/matplotlib/issues/18580"}