code: def find_selected(self, event):
          '''find the selected menu item'''
          if event.GetId() == self.id():
              self.checked = event.IsChecked()
              return self
          return Nonf find_selected(self, event):
          '''find the selected menu item'''
          if event.GetId() == self.id():
              self.checked = event.IsChecked()
              return self
          return None
docs: find the selected menu item