Using MPI with Cython and C++. Specifically, using Cython to make Python wrappers for C++ code that uses MPI.

hello_world.py

# Make sure to call this first to initialize MPI
from mpi4py import MPI
from pympi import *

stats = mpi_stats()

print "Hello from process %i of %i!" % (stats.rank, stats.size)

Makefile

all:
	python setup.py build_ext --inplace

clean:
	rm -f pympi.cpp
	rm -f pympi.so
	rm -rf build

mpi_stats.cpp

#include "mpi.h"
#include "mpi_stats.hpp"

// You could call these from mpi4py...
// but what would be the fun in that!

bool check_mpi()
{
  int flag;
  MPI_Initialized(&flag);
  return flag == 1;
}

int get_rank()
{
  int rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  return rank;
}

int get_comm_size()
{
  int numtasks;
  MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
  return numtasks;
}

int thread_level()
{
  int provided = -1;
  if(check_mpi()) 
    MPI_Query_thread(&provided);

  return provided;
}

bool has_thread_multiple()
{
  return thread_level() == MPI_THREAD_MULTIPLE;
}

mpi_stats.hpp

#ifndef __MPI_STATS_H
#define __MPI_STATS_H

#include "mpi.h"

bool check_mpi();

int get_rank();

int get_comm_size();

int thread_level();

bool has_thread_multiple();

#endif

pympi.pyx

from collections import namedtuple, Iterable

from libcpp cimport bool

cdef extern from "mpi_stats.hpp":
    bool check_mpi()
    int get_rank()
    int get_comm_size()
    int thread_level()
    bool has_thread_multiple()

MPIStats = namedtuple("MPIStats", ["check_mpi", "rank", "size",
                                   "thread_level", "has_thread_multiple"])

def mpi_stats():
    return MPIStats(check_mpi(), get_rank(), get_comm_size(),
                    thread_level(), has_thread_multiple())

run_examples.sh

echo Checking MPI stats
mpirun -n 4 python stats.py

echo
echo Running hello_world
mpirun -n 4 python hello_world.py

setup.py

import os
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext

mpi_compile_args = os.popen("mpic++ --showme:compile").read().strip().split(' ')
mpi_link_args    = os.popen("mpic++ --showme:link").read().strip().split(' ')

ext_modules=[
    Extension("pympi",
              sources            = ["pympi.pyx", "mpi_stats.cpp"],
              language           = 'c++',
              extra_compile_args = mpi_compile_args,
              extra_link_args    = mpi_link_args,
          )
]

setup(
  name = "pympi",
  cmdclass = {"build_ext": build_ext},
  ext_modules = ext_modules
)

stats.py

# Make sure to call this first to initialize MPI
from mpi4py import MPI
from pympi import *

print mpi_stats()