code: def _value_iterator(self, task_name, param_name):
          
          cp_parser = CmdlineParser.get_instance()
          if cp_parser:
              dest = self._parser_global_dest(param_name, task_name)
              found = getattr(cp_parser.known_args, dest, None)
              yield (self._parse_or_no_value(found), None)
          yield (self._get_value_from_config(task_name, param_name), None)
          if self._config_path:
              yield (self._get_value_from_config(self._config_path['section'], self._config_path['name']),
                     'The use of the configuration [{}] {} is deprecated. Please use [{}] {}'.format(
                         self._config_path['section'], self._config_path['name'], task_name, param_name))
          yield (self._default, None)
docs: Yield the parameter values, with optional deprecation warning as second tuple value.
  
          The parameter value will be whatever non-_no_value that is yielded first.