I've just wasted a whole day trying to debug my event-handling code that intercepted the 'key_press_event'. In the end it turned out the key I was trying to handle ('l') was a known keyboard shortcut for Matplotlib at https://matplotlib.org/users/navigation_toolbar.html#navigation-keyboard-shortcuts and that all I had to do was use a different letter instead: a one-character fix!

I might have been less likely to have made this mistake had there been some reference to the pre-defined keyboard shortcuts somewhere in the event-handling tutorial at https://matplotlib.org/users/event_handling.html. Perhaps have a note next to the entries for the 'key_press_event' and 'key_release_event' in the table of events under https://matplotlib.org/users/event_handling.html#event-connections ? In general, though, the Matplotlib docs are superb.