code: def toggle_custom_value(self):
          
          radio_button_checked_id = self.input_button_group.checkedId()
          if (radio_button_checked_id
                  == len(self._parameter.options) - 1):
              self.custom_value.setDisabled(False)
          else:
              self.custom_value.setDisabled(True)
docs: Enable or disable the custom value line edit.