The issue you are having is due to the way that gui mainloops work. When ever you plot call draw
events get added to the queue of events for the main loop to process. If you add them as fast as possible the loop can never clear it's queue and actually draw to the screen.
Adding a plt.pause(.1)
will pause the loop and allow the main loop (at the risk of being anthropomorphic) 'catch it's breath' and update the widgets on the screen
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