code: def update_dropdown_list_slot(self):
          
          self.dropdown_widget.clear() # this will trigger dropdown_changed_slot
          self.row_instance_by_index = []
          for i, key in enumerate(self.row_instance_by_name.keys()):
              row_instance = self.row_instance_by_name[key]
              if (row_instance.isActive()):
                  self.row_instance_by_index.append(row_instance)
                  display_name = row_instance.getName()
                  self.dropdown_widget.insertItem(i, display_name)
              row_instance.updateWidget()
docs: Keep updating the dropdown list.  Say, don't let the user choose USB devices if none is available