code from http://www.masnun.com/2014/01/01/async-execution-in-python-using-multiprocessing-pool.html

asyncfactory.py

from multiprocessing import Pool
from time import sleep
from random import randint
import os

class AsyncFactory:
    def __init__(self, num_procs,func, cb_func):
        self.func = func
        self.cb_func = cb_func
        self.pool = Pool(processes=num_procs)

    def call(self,*args, **kwargs):
        self.pool.apply_async(self.func, args, kwargs, self.cb_func)

    def wait(self):
        self.pool.close()
        self.pool.join()

    @staticmethod
    def cb_func(x):
        print x

work.py

from asyncfactory import AsyncFactory

def func(data):
    #...do heavy stuff
    return data


if __name__ == '__main__':
    data = ".."
    number_of_threads = 8
    async_work = AsyncFactory(number_of_threads, func, AsyncFactory.cb_func)
    for item in data:
            async_work.call(data)