[Matplotlib-users] Please advise...How to detect if a user has closed the matplotlib figure window?

Good day,

With a previous version of matplotlib, I was able to plot 4 axes on a figure and update it, in a while loop, with plt.pause().
If the figure window was closed by the user, the plt.pause() would signal an error and I was able to escape the while loop using try/except.

try: #

plt.pause(0.05) #

if gv.saveImage_UserCancel:

H1_FinishingOptions.saveImage(temp_name=f"{Names.processName}", option=2) #

except: # This allows the closing of graph display window and going back to OED main menu. Variables and lists are reset for next scan. #

if gv.multWafers_lastWaferDetected: #

H1_FinishingOptions.UserCancelled(time_lst=H1_waferScan_time_lst, select=‘single’) #

process.cprint(‘END’) #

break #

elif not gv.multWafers_lastWaferDetected: #

H1_FinishingOptions.UserCancelled(time_lst=H1_waferScan_time_lst, select=‘multiple’) #

break #

With the new release of matplotlib, I’m no longer triggering an error when the figure window is manually closed, and the program then stalls in a loop because of the plt.pause().

File “c:/Users/ABillings/AppData/Local/Programs/Python/Python37/MyPythonDocs/Endpoint-08.19.21(Samtec).py”, line 12576, in epMain


File “C:\Users\ABillings\AppData\Local\Programs\Python\Python37\lib\site-packages\matplotlib\pyplot.py”, line 558, in pause


File “C:\Users\ABillings\AppData\Local\Programs\Python\Python37\lib\site-packages\matplotlib\backends_backend_tk.py”, line 385, in start_event_loop


File “C:\Users\ABillings\AppData\Local\Programs\Python\Python37\lib\tkinter_init_.py”, line 1283, in mainloop



I’m now trying things like below, but to no avail. I need to somehow get the program to break the while loop when it detects a user has closed the figure window.

Is there a method I can call to check whether the figure is still opened and make a decision based on that?

That’s what I’m trying to do here, but the code stalls in the plt.pause() every time.

if not plt.fignum_exists(1):

print(f"plt.get_axes() is False")





print(f"plt.get_axes() is True")



print(“Before Pause”)


print(“After Pause”)

Please and thank you.

What error did we use to raise? I would not have expected that.

You can use the close_event to be notified what the window is closed (see https://matplotlib.org/stable/gallery/event_handling/close_event.html). You can probably also keep a reference to the Figure you create and query its state.

From this code snippet I can not tell if you are embedding Matplotlib in a bigger GUI application or not. If you are, you can rely on it’s main loop to be spinning so you do not actually need plt.pause().



Thomas Caswell