code: def on_display_n_changed(self, combo):
          
  
          i = combo.get_active_iter()
          if not i:
              return
  
          model = combo.get_model()
          first_item_path = model.get_path(model.get_iter_first())
  
          if model.get_path(i) == first_item_path:
              val_int = ALWAYS_ON_PRIMARY
          else:
              val = model.get_value(i, 0)
              val_int = int(val.split()[0])  # extracts 1 from '1' or from '1 (primary)'
          self.settings.general.set_int('display-n', val_int)
docs: Set the destination display in dconf.