code: def init_inter_mpi_comm(mpi_comm, intra_rank, inter_rank):
      return mpi_comm.Split(intra_rank, inter_rank)
  
file_path: chainer/chainermn/communicators/_communication_utility.py
imports: from chainermn import nccl
  import collections
  import numpy
  import pickle
  import mpi4py.MPI
label_desc: Use image node_id 3 for calling a global function with example usage: init_inter_mpi_comm(mpi_comm, intra_rank, inter_rank) and returns: mpi_comm