Initialize/Build the ``argparse.ArgumentParser`` and subparsers.

        This internal version of ``init`` is used to ensure that all
        subcommands have a properly initialized parser.

        Args
        ----
        parser : argparse.ArgumentParser
            The parser for this command.

def _init(self, parser):
        """Initialize/Build the ``argparse.ArgumentParser`` and subparsers.

        This internal version of ``init`` is used to ensure that all
        subcommands have a properly initialized parser.

        Args
        ----
        parser : argparse.ArgumentParser
            The parser for this command.

        """
        assert isinstance(parser, argparse.ArgumentParser)
        self._init_parser(parser)

        self._attach_arguments()
        self._attach_subcommands()
        self.initialized = True