<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _parse_custom_mpi_options(custom_mpi_options):
 # type: (str) -> Tuple[argparse.Namespace, List[str]] """Parse custom MPI options provided by user. Known options default value will be overridden and unknown options would be identified separately."""


    parser = argparse.ArgumentParser()
    parser.add_argument('--NCCL_DEBUG', default="INFO", type=str)

    return parser.parse_known_args(custom_mpi_options.split())