<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def onLeftUp(self, event=None):
 """ left button up"""

        if event is None:
            return
        self.cursor_mode_action('leftup', event=event)
        self.canvas.draw_idle()
        self.canvas.draw()
        self.ForwardEvent(event=event.guiEvent)