Parallelize these nested for loops in python

Question

I have a multidimensional array (result) that should be filled by some nested loops. Function fun() is a complex and time-consuming function. I wan

Answer 1

A simple approach could be to divide the array in sections and create some threads to operate throught these sections. For example one section from (0,0,0) to (5,10,15) and other one from (5,10,16) to (10,20,30).

You can use threading module and do something like this

import numpy as np
import threading as t


def fun(x, y, z):
    # time-consuming computation...
    # ...

    return output


dim1 = 10
dim2 = 20
dim3 = 30

result = np.zeros([dim1, dim2, dim3])
#b - beginning index, e - end index
def work(ib,jb,kb,ie,je,ke):
    for i in xrange(ib,ie):
        for j in xrange(jb,je):
            for k in xrange(kb,ke):
                result[i, j, k] = fun(i, j, k)

 threads = list()
 threads.append(t.Thread(target=work, args(0,0,0,dim1/2,dim2/2,dim3/2))
 threads.append(t.Thread(target=work, args(dim1/2,dim2/2,dim3/2 +1,dim1, dim2, dim3))

 for thread in threads:
     thread.start()

You can define these sections through some algorithm and determine the number of threads dynamically. Hope it helps you or at least give you some ideas.