code: def set_backend(backend):
      if not use_ds_backend:
          utils.logger.error(
              "DeepSpeed communication backend is required. Please use deepspeed.comm.init_distributed(backend, use_deepspeed=True) to use this functionality"
          )
          raise RuntimeError(
              "Error: Custom DeepSpeed backend called without initializing DeepSpeed distributed."
          )
  
      global cdb
      global nccl_backend
      global mpi_backend
  
      try:
          if backend_name == NCCL_BACKEND:
              if (
                  nccl_backend is not None
                  and nccl_backend.is_initialized()
              ):
                  cdb = nccl_backend
          elif backend_name == MPI_BACKEND:
              if (
                  mpi_backend is not None
                  and mpi_backend.is_initialized()
              ):
                  cdb = mpi_backend
      except Exception as inst:
          print(inst)
  
imports: from enum import Enum
  import torch
  import os
  from ..constants import TORCH_DISTRIBUTED_DEFAULT_PORT, default_pg_timeout
  from .constants import *
  from deepspeed.utils.comms_logging import CommsLogger
  from deepspeed.utils import timer, get_caller_func
  from deepspeed.comm.torch import TorchBackend
  from deepspeed import utils
  from datetime import timedelta
  from deepspeed.comm.utils import *
label_desc: Use image node_id 9 for calling a global function with example usage: set_backend(backend) without return types