code: def register_on_guest_keyboard(self, callback):
          
          return self.event_source.register_callback(callback,
                                                     library.VBoxEventType.on_guest_keyboard)
docs: Set the callback function to consume on guest keyboard events
  
          Callback receives a IGuestKeyboardEvent object.
  
          Example:
              def callback(event):
                  print(event.scancodes)