docs: def onpress(self, event):
          """
          Reacts to key commands
          :param event: a keyboard event
          :return: if 'c' is pressed, clear all region patches
          """
          if event.key == 'c':  # clears all the contours
              for patch in self.region_patches:
                  patch.remove()
              self.region_patches = []
              self.fig.canvas.draw_idle()
          elif event.key == "u":  # undo a label
              self.undobutton_action()