how to kill a process's child processes in python

kill_child_processes.py

#!/usr/bin/env python

import multiprocessing
import time
import subprocess, os, signal, sys

def test(s):
    while True:
        print s
        time.sleep(1.5)

def kill_child_processes(signum, frame):
    parent_id = os.getpid()
    ps_command = subprocess.Popen("ps -o pid --ppid %d --noheaders" % parent_id, shell=True, stdout=subprocess.PIPE)
    ps_output = ps_command.stdout.read()
    retcode = ps_command.wait()
    for pid_str in ps_output.strip().split("\n")[:-1]:
        os.kill(int(pid_str), signal.SIGTERM)
    sys.exit()

if __name__ == '__main__':
    pool = multiprocessing.Pool(processes=4)
    result = pool.map_async(test, 'abcd')
    signal.signal(signal.SIGTERM, kill_child_processes)
    result.get(10000)
    pool.close()
    pool.join()