def parse_args(prog: Optional[str] = None) -> Tuple[argparse.ArgumentParser, argparse.Namespace]:
    """
    Creates the argument parser for the main program and uses it to parse the args.
    """
    parser = ArgumentParserWithDefaults(description="Run AllenNLP", prog=prog)
    parser.add_argument("--version", action="version", version=f"%(prog)s {__version__}")

    subparsers = parser.add_subparsers(title="Commands", metavar="")

    subcommands: Set[str] = set()

    def add_subcommands():
        for subcommand_name in sorted(Subcommand.list_available()):
            if subcommand_name in subcommands:
                continue
            subcommands.add(subcommand_name)
            subcommand_class = Subcommand.by_name(subcommand_name)
            subcommand = subcommand_class()
            subparser = subcommand.add_subparser(subparsers)
            if subcommand_class.requires_plugins:
                subparser.add_argument(
                    "--include-package",
                    type=str,
                    action="append",
                    default=[],
                    help="additional packages to include",
                )

    # Add all default registered subcommands first.
    add_subcommands()

    # If we need to print the usage/help, or the subcommand is unknown,
    # we'll call `import_plugins()` to register any plugin subcommands first.
    argv = sys.argv[1:]
    plugins_imported: bool = False
    if not argv or argv == ["--help"] or argv[0] not in subcommands:
        import_plugins()
        plugins_imported = True
        # Add subcommands again in case one of the plugins has a registered subcommand.
        add_subcommands()

    # Now we can parse the arguments.
    args = parser.parse_args()

    if not plugins_imported and Subcommand.by_name(argv[0]).requires_plugins:  # type: ignore
        import_plugins()

    return parser, args
Creates the argument parser for the main program and uses it to parse the args.
allennlp/commands/__init__.py