sum_p2p.py

from mpi4py import MPI

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

val = (rank+1)*10
print("Rank %d has value %d" %(rank, val))

if rank == 0:
    sum = val
    for i in range(1, size):
        sum += comm.recv(source=i)
    print("Rank 0 worked out the total %d" %sum)

else:
    comm.send(val, dest=0)