def last_event(self):
        """ The mouse event immediately prior to this one. This
        property is None when no mouse buttons are pressed.
        """
        if self.mouse_event.last_event is None:
            return None
        ev = self.copy()
        ev.mouse_event = self.mouse_event.last_event
        return ev
The mouse event immediately prior to this one. This
        property is None when no mouse buttons are pressed.