code: def _parse_custom_mpi_options(custom_mpi_options):
      # type: (str) -> Tuple[argparse.Namespace, List[str]]
      
  
      parser = argparse.ArgumentParser()
      parser.add_argument('--NCCL_DEBUG', default="INFO", type=str)
  
      return parser.parse_known_args(custom_mpi_options.split())
docs: Parse custom MPI options provided by user. Known options default value will be overridden
      and unknown options would be identified separately.