mpi-msg-chain.py

from mpi4py import MPI
import numpy

comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()

data = numpy.arange(10, dtype=float) * (rank + 1)  # send buffer
buffer = numpy.zeros(10, dtype=float)              # receive buffer

tgt = rank + 1
src = rank - 1
if rank == 0:
    src = MPI.PROC_NULL
if rank == size - 1:
    tgt = MPI.PROC_NULL

req = []
req.append(comm.Isend(data, dest=tgt))
req.append(comm.Irecv(buffer, source=src))

MPI.Request.waitall(req)

print('[{0:2}] Received: {1}'.format(rank, buffer))