code: def mpi_env_rank_and_size():
      """Get MPI rank and size from environment variables and return them as a
      tuple of integers.
  
      Most MPI implementations have an `mpirun` or `mpiexec` command that will
      run an MPI executable and set up all communication necessary between the
      different processors. As part of that set up, they will set environment
      variables that contain the rank and size of the MPI_COMM_WORLD
      communicator. We can read those environment variables from Python in order
      to ensure that `hvd.rank()` and `hvd.size()` return the expected values.
  
      Since MPI is just a standard, not an implementation, implementations
      typically choose their own environment variable names. This function tries
      to support several different implementation, but really it only needs to
      support whatever implementation we want to use for the TensorFlow test
      suite.
  
      If this is not running under MPI, then defaults of rank zero and size one
      are returned. (This is appropriate because when you call MPI_Init in an
      application not started with mpirun, it will create a new independent
      communicator with only one process in it.)
      """
      rank_env = "PMI_RANK OMPI_COMM_WORLD_RANK".split()
      size_env = "PMI_SIZE OMPI_COMM_WORLD_SIZE".split()
  
      for rank_var, size_var in zip(rank_env, size_env):
          rank = os.environ.get(rank_var)
          size = os.environ.get(size_var)
          if rank is not None and size is not None:
              return int(rank), int(size)
  
      # Default to rank zero and size one if there are no environment variables
      return 0, 1
  
imports: import contextlib
  import multiprocessing
  import os
  import shutil
  import sys
  import tempfile
  import time
  import traceback
  import cloudpickle
  import mock
  from horovod.runner.util.threads import in_thread
label_desc: Use image node_id 1 for calling a global function with example usage: mpi_env_rank_and_size() and returns: int,  int, int,  int