code: def find_selected(self, event):
          '''find the selected menu item'''
          for m in self.items:
              ret = m.find_selected(event)
              if ret is not None:
                  return ret
          return Nonf find_selected(self, event):
          '''find the selected menu item'''
          for m in self.items:
              ret = m.find_selected(event)
              if ret is not None:
                  return ret
          return None
docs: find the selected menu item