def serve_handler(self, button): """ Callback when serve button was pressed. """ button_pos = list(button.to_window(*button.pos)) button_pos[0] -= 100 beer = Beer(lane=button.lane) button.lane.puck_area.add_widget(beer) button.lane.beers.append(beer) beer.pos = beer.to_local(button_pos[0], 15)