the interactions between objects when the user selects one of the menu items the command_menu_handler (method of the pydrawcontroller is invoked this method determines which menu item has been selectedit then calls an appropriate setter method (such as set_circle_mode(or set_line_mode(etc these methods set the mode attribute of the controller to an appropriate value adding graphic object user adds graphic object to the drawing displayed by the drawingpanel by pressing the mouse button when the user clicks on the drawing panelthe drawingcontroller responds as shown below