code: def hier_setup():
      os.environ["BLUEFOG_NODES_PER_MACHINE"] = "2"
      bf.init()
      assert bf.size() % 2 == 0
      machine_size = int(bf.size() // 2)
      bf.set_machine_topology(bf.ExponentialGraph(machine_size))
      return bf.rank(), bf.size(), bf.local_rank(), bf.local_size()
  
imports: import itertools
  import os
  import numpy
  import pytest
  import torch
  import networkx
  import bluefog.torch
  from common import mpi_env_rank_and_size
label_desc: Use image node_id 4 for calling a global function with example usage: hier_setup() and returns: bf,  bf,  bf,  bf