Python argparse 模块，_AppendAction() 实例源码

def convert_item_to_command_line_arg(self, action, key, value):
        """Converts a config file or env var key + value to a list of
        commandline args to append to the commandline.

        Args:
            action: The argparse Action object for this setting, or None if this
                config file setting doesn't correspond to any defined
                configargparse arg.
            key: string (config file key or env var name)
            value: parsed value of type string or list
        """
        args = []
        if action is None:
            command_line_key = \
                self.get_command_line_key_for_unknown_config_file_setting(key)
        else:
            command_line_key = action.option_strings[-1]

        # handle boolean value
        if action is not None and isinstance(action, ACTION_TYPES_THAT_DONT_NEED_A_VALUE):
            if value.lower() in ("true", "yes"):
                args.append( command_line_key )
            elif value.lower() in ("false", "no"):
                # don't append when set to "false" / "no"
                pass
            else:
                self.error("Unexpected value for %s: '%s'. Expecting 'true', "
                           "'false', 'yes', or 'no'" % (key, value))
        elif isinstance(value, list):
            if action is None or isinstance(action, argparse._AppendAction):
                for list_elem in value:
                    args.append( command_line_key )
                    args.append( str(list_elem) )
            elif (isinstance(action, argparse._StoreAction) and action.nargs in ('+', '*')) or (
                isinstance(action.nargs, int) and action.nargs > 1):
                args.append( command_line_key )
                for list_elem in value:
                    args.append( str(list_elem) )
            else:
                self.error(("%s can't be set to a list '%s' unless its action type is changed "
                            "to 'append' or nargs is set to '*', '+', or > 1") % (key, value))
        elif isinstance(value, str):
            args.append( command_line_key )
            args.append( value )
        else:
            raise ValueError("Unexpected value type %s for value: %s" % (
                type(value), value))

        return args