matplotlib plot does not appear in debug mode

[vainaixr]

when I attempt at plotting an image after set_trace(), it does not appear while debugging

[tacaswell]

This is because the input hook (see matplotlib/matplotlib#4779 for gory details) is not active in the debugger so the GUI framework never gets the chance to run its event loop and update the windows.

You can do plt.pause(1) (run the GUI for 1s), plt.show(block=True) (run the GUI until you close al of the open windows), or fig.canvas.flush_events() (process the current event queue in the GUI) to get responsive (ish) windows.