python Multiprocess with two list compare

Question

I have the question on multiprocess in python3.5.

If i have two list like:

xlist = [1,2,3]
ylist = [4,5,6]

and I want to do :

for i in xlist:
    for j in ylist:
        print (i*j)

the output is

4
5
6
8
10
12
12
15
18

I try to do that like this with Multiprocess:

import multiprocessing

global xlist
xlist = [1,2,3]
ylist = [4,5,6]

def product(ylist): 
    for x in xlist:
        for y in ylist:
            print (x,y)
    return 'OK'

if __name__ == "__main__":
    pool = multiprocessing.Pool()
    results = []
    for i in range(0, len(ylist)):
        result = pool.apply_async(job, args=(ylist,))
        results.append(result)
        # print (result.get())
    pool.close()
    pool.join()

for result in results:
    print(result.get())

But I can not got the output show above. My output will be

1 4
1 5
1 6
2 4
2 5
2 6
3 4
3 5
3 6
1 4
1 5
1 6
2 4
2 5
2 6
3 4
3 5
3 6
1 4
1 5
...

with the code.

Are there any ways to achieve the goal (must use multiprocess)?

Answer 1

I think you want to try a simple example before using it on a very big set of numbers, and with a more complex function.

Here is one program that prints what you want, uses multiprocessing, and should scale for larger lists and more complex functions.

import multiprocessing

xlist=[1,2,3]
ylist=[4,5,6]

def enum_tasks():
  for x in xlist:
    for y in ylist:
      yield (x,y)

def product(xy):
  x,y = xy
  return x * y

if __name__ == '__main__':
  CHUNK_SIZE = multiprocessing.cpu_count()
  pool = multiprocessing.Pool()
  for result in pool.imap(product, enum_tasks(), CHUNK_SIZE):
    print result