Parsing arguments using argparse and mpi4py

The extra piece I needed was to wrap a try/finally around the argument parsing step in process 0. In the finally block, broadcast something to the other processes. If parsing failed, you will broadcast None, and they can all silently exit.

from mpi4py import MPI
from time import sleep
import argparse

def parseOptions(comm):
    parser = argparse.ArgumentParser(
        description='Print some messages.')

    parser.add_argument('iteration_count', help='How many times', type=int)
    parser.add_argument('message',
                        help='What to say',
                        nargs=argparse.OPTIONAL,
                        default='Hello, World!')

    args = None
    try:
        if comm.Get_rank() == 0:
            args = parser.parse_args()
    finally:
        args = comm.bcast(args, root=0)

    if args is None:
        exit(0)
    return args

def main():
    comm = MPI.COMM_WORLD  # @UndefinedVariable
    rank = comm.Get_rank()
    size = comm.Get_size()

    args = parseOptions(comm)

    if rank == 0:
        print args.message

    for i in range(args.iteration_count):
        if i%size == rank:
            print '{} in rank {} started.'.format(i, rank)
            sleep(.5)
            print '...'
            sleep(.5)
            print '{} in rank {} ended.'.format(i, rank)

if __name__ == '__main__':
    main()

I run the code with a command like this:

mpirun -np 4 python scratch.py 13

If you have an error case, it's usually easiest to just have the processes abort rather than trying to do something fancy to clean up. In your case, you could just have the origin process (rank 0) call abort and cause everyone else to quit:

comm.abort()

That way, you don't have everyone trying to match up the results. They just automatically abort.