code: def handle_scrollwheel(self, event):
          
          # relative Scrollwheel
          scroll_x, scroll_y = self._get_scroll(event)
  
          if scroll_x:
              self.events.append(
                  self.emulate_wheel(scroll_x, 'x', self.timeval))
  
          if scroll_y:
              self.events.append(
                  self.emulate_wheel(scroll_y, 'y', self.timeval))
docs: Handle the scrollwheel (it is a ball on the mighty mouse).