code: def accel_next(self, *args):
          
          if self.get_notebook().get_current_page() + 1 == self.get_notebook().get_n_pages():
              self.get_notebook().set_current_page(0)
          else:
              self.get_notebook().next_page()
          return True
docs: Callback to go to the next tab. Called by the accel key.