arg_parsing.py 文件源码

def __call__(
            self,
            parser,  # type: argparse.ArgumentParser
            namespace,  # type: argparse.Namespace
            values,  # type: Union[ARGPARSE_TEXT, Sequence[Any], None]
            option_string=None  # type: Optional[ARGPARSE_TEXT]
    ):
        # type: (...) -> None
        """Checks to make sure that the destination is empty before writing.

        :raises parser.error: if destination is already set
        """
        if getattr(namespace, self.dest) is not None:  # type: ignore # typeshed doesn't know about Action.dest yet?
            parser.error('{} argument may not be specified more than once'.format(option_string))
            return
        setattr(namespace, self.dest, values)  # type: ignore # typeshed doesn't know about Action.dest yet?