MPI4PY: ring communication with neighbor_alltoallw - python-3.x

Question

Please Help!
I am using MPI (= Message Passing Interface) in python for a ring communication, which means that every rank are sending and receiving from each other. I know one way to realize this is by using for instance MPI.COMM_WORLD.issend()and MPI.COMM_WORLD.recv(), this is working and done.
Now I want to realize the same Output on a different way by using MPI.Topocomm.Neighbor_alltoallw but this is not working. I wrote a C Code and is working there, so the same output can be reached with this function, but when I implement this in python it is not working. Please find below the C Code and the Python Code
The definition of the Function says (mpi4py Package for Python):
Neighbor_alltoallw(...)
Topocomm.Neighbor_alltoallw(self, sendbuf, recvbuf)
Neighbor All-to-All Generalized
I do not understand following things:
why is recbuf not a return value? it seems to be an argument here
how can this be implmented for a ring communication in Python?
Thank you for your time and support!
my working C Code:
#include <stdio.h>
#include <mpi.h>
#define to_right 201
#define max_dims 1
int main (int argc, char *argv[])
{
int my_rank, size;
int snd_buf, rcv_buf;
int right, left;
int sum, i;
MPI_Comm new_comm;
int dims[max_dims],
periods[max_dims],
reorder;
MPI_Aint snd_displs[2], rcv_displs[2];
int snd_counts[2], rcv_counts[2];
MPI_Datatype snd_types[2], rcv_types[2];
MPI_Status status;
MPI_Request request;
MPI_Init(&argc, &argv);
/* Get process info. */
MPI_Comm_size(MPI_COMM_WORLD, &size);
/* Set cartesian topology. */
dims[0] = size;
periods[0] = 1;
reorder = 1;
MPI_Cart_create(MPI_COMM_WORLD, max_dims, dims, periods,
reorder,&new_comm);
/* Get coords */
MPI_Comm_rank(new_comm, &my_rank);
/* MPI_Cart_coords(new_comm, my_rank, max_dims, my_coords); */
/* Get nearest neighbour rank. */
MPI_Cart_shift(new_comm, 0, 1, &left, &right);
/* Compute global sum. */
sum = 0;
snd_buf = my_rank;
rcv_buf = -1000; /* unused value, should be overwritten by first MPI_Recv; only for test purpose */
rcv_counts[0] = 1; MPI_Get_address(&rcv_buf, &rcv_displs[0]); snd_types[0] = MPI_INT;
rcv_counts[1] = 0; rcv_displs[1] = 0 /*unused*/; snd_types[1] = MPI_INT;
snd_counts[0] = 0; snd_displs[0] = 0 /*unused*/; rcv_types[0] = MPI_INT;
snd_counts[1] = 1; MPI_Get_address(&snd_buf, &snd_displs[1]); rcv_types[1] = MPI_INT;
for( i = 0; i < size; i++)
{
/* Substituted by MPI_Neighbor_alltoallw() :
MPI_Issend(&snd_buf, 1, MPI_INT, right, to_right,
new_comm, &request);
MPI_Recv(&rcv_buf, 1, MPI_INT, left, to_right,
new_comm, &status);
MPI_Wait(&request, &status);
*/
MPI_Neighbor_alltoallw(MPI_BOTTOM, snd_counts, snd_displs, snd_types,
MPI_BOTTOM, rcv_counts, rcv_displs, rcv_types, new_comm);
snd_buf = rcv_buf;
sum += rcv_buf;
}
printf ("PE%i:\tSum = %i\n", my_rank, sum);
MPI_Finalize();
}
My not working Python Code:
from mpi4py import MPI
size = MPI.COMM_WORLD.Get_size()
my_rank = MPI.COMM_WORLD.Get_rank()
to_right =201
max_dims=1
dims = [max_dims]
periods=[max_dims]
dims[0]=size
periods[0]=1
reorder = True
new_comm=MPI.Intracomm.Create_cart(MPI.COMM_WORLD,dims,periods,True)
my_rank= new_comm.Get_rank()
left_right= MPI.Cartcomm.Shift(new_comm,0,1)
left=left_right[0]
right=left_right[1]
sum=0
snd_buf=my_rank
rcv_buf=-1000 #unused value, should be overwritten, only for test purpose
for counter in range(0,size):
MPI.Topocomm.Neighbor_alltoallw(new_comm,snd_buf,rcv_buf)
snd_buf=rcv_buf
sum=sum+rcv_buf
print('PE ', my_rank,'sum=',sum)