René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Tkagg event loop throws error on window close","articleBody":"I have some code that continuously updates an MPL plot, and used `fig.canvas.start_event_loop(0.0001)` to listen for keyboard input. As of MPL 3.4, this code is broken in two ways:\r\n\r\n1. [Commit c53570d](https://github.com/matplotlib/matplotlib/commit/c53570db3e602d2855813fa76a971ae3b62d361a) converts the timeout to int milliseconds. This rounds down 0.0001 to 0 and fails to display the window at all. I might suggest `math.ceil(1000*timeout)` instead of `int(1000*timeout)`?\r\n2. After changing 0.0001 to 0.001 in my code, [Commit 630e806](https://github.com/matplotlib/matplotlib/commit/630e806ef7dfd0520490eeb85d2c866d8f8dca94) causes MPL to throw an error `invalid command name \"140668474408832stop_event_loop\" while executing \"140668474408832stop_event_loop\" (\"after\" script)` when closing the window before pausing the loop. Expected behavior would be for it to simply terminate the loop. It's a harmless error in the minimal code below (you can still launch new runs), but my full code updates using an `asyncio` event loop, which this behavior fails to exit, so this error prevents launching new runs in that case (`asyncio.run() cannot be called from a running event loop`). Not sure how to fix this one, but I'll note that using `fig.canvas.flush_events()` in my code instead of `start_event_loop` produces the desired behavior.\r\n\r\nNot sure if #2 is worth fixing given that `flush_events()` restores the desired behavior, but @richardsheridan suggested I post an issue in my comment on that commit. Minimal example below. Launch an MPL window and then close it before pausing to trigger the error:\r\n\r\n```\r\nfrom random import randint\r\nimport matplotlib, matplotlib.pyplot as plt\r\nfrom tkinter import *\r\n\r\nclass Visual:\r\n\trunning = False\r\n\t\r\n\t#Construct a launch button\r\n\tdef __init__(self):\r\n\t\tself.parent = Tk()\r\n\t\t\r\n\t\tself.runButton = Button(self.parent, text='Run', command=self.launchVisual, padx=10, pady=10)\r\n\t\tself.runButton.pack(fill=\"x\", side=TOP)\r\n\t\t\t\t\t\r\n\tdef start(self):\r\n\t\tself.runButton['text'] = 'Pause'\r\n\t\tself.runButton['command'] = self.stop\r\n\t\tself.running = True\r\n\t\t\r\n\t\twhile self.running:\r\n\t\t\tself.data.append(randint(0,100))\r\n\t\t\r\n\t\t\tself.line.set_ydata(self.data)\r\n\t\t\tself.line.set_xdata(range(len(self.data)))\r\n\t\t\tself.axes.relim()\r\n\t\t\tself.axes.autoscale_view(tight=False)\r\n\t\t\r\n\t\t\tif self.fig.stale: self.fig.canvas.draw_idle()\r\n\t\t\t\r\n\t\t\t#This rounds down to 0 and doesn't draw the window at all\r\n\t\t\t#self.fig.canvas.start_event_loop(0.0001)\r\n\t\t\t\r\n\t\t\t#This throws an error and breaks asyncio if you close the window before pausing\r\n\t\t\tself.fig.canvas.start_event_loop(0.001)\r\n\t\t\r\n\t\t\t#This works\r\n\t\t\t#self.fig.canvas.flush_events()\r\n\t\r\n\tdef stop(self, *args):\r\n\t\tself.running = False\r\n\t\tself.runButton['text'] = 'Run'\r\n\t\tself.runButton['command'] = self.start\r\n\t\r\n\tdef terminate(self, evt=False):\r\n\t\tself.running = False\r\n\t\tself.runButton['text'] = 'New Model'\r\n\t\tself.runButton['command'] = self.launchVisual\r\n\t\t\r\n\tdef launchVisual(self):\r\n\t\tmatplotlib.use('TkAgg')\r\n\t\tself.fig, self.axes = plt.subplots()\r\n\t\tself.fig.canvas.mpl_connect('close_event', self.terminate)\r\n\t\t\r\n\t\t#Keyboard input\r\n\t\tdef pause(event):\r\n\t\t\tif event.key==' ' and event.canvas is self.fig.canvas:\r\n\t\t\t\tif self.running: self.stop()\r\n\t\t\t\telse: self.start()\r\n\t\tself.fig.canvas.mpl_connect('key_press_event', pause)\r\n\t\t\r\n\t\tself.data = []\r\n\t\tself.line, = self.axes.plot(self.data, color='#330099')\r\n\t\t\r\n\t\tself.fig.canvas.draw_idle()\r\n\t\tplt.show(block=False)\r\n\t\t\r\n\t\tself.start()\r\n\r\nviz = Visual()\r\nviz.parent.mainloop()\r\n```","author":{"url":"https://github.com/charwick","@type":"Person","name":"charwick"},"datePublished":"2021-04-11T19:15:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/19940/matplotlib/issues/19940"}