def _required_argument(name, arg):
    """Process a required argument"""
    if arg.args and arg.args[0] != name:
        raise ValueError(
            "Positional argument '{0}' must have the same name as the function argument, '{1}'"
            .format(arg.args[0], name))
    elif not arg.args:
        arg.args = name,
    arg.kwargs.update(metavar=arg.kwargs.get('metavar', '<{0}>'.format(name)))
    return arg
