code: def mpi_fork(n, extra_mpi_args=[]):
      
      if n <= 1:
          return "child"
      if os.getenv("IN_MPI") is None:
          env = os.environ.copy()
          env.update(
              MKL_NUM_THREADS="1",
              OMP_NUM_THREADS="1",
              IN_MPI="1"
          )
          # "-bind-to core" is crucial for good performance
          args = ["mpirun", "-np", str(n)] + \
              extra_mpi_args + \
              [sys.executable]
  
          args += sys.argv
          subprocess.check_call(args, env=env)
          return "parent"
      else:
          install_mpi_excepthook()
          return "child"
docs: Re-launches the current script with workers
      Returns "parent" for original parent, "child" for MPI children