python2 and python3 multiprocessing error

Question

I am running the below script in python2 and python3 environment.

import subprocess as sub
import sys
#import time
import multiprocessing, time, signal
def tcpdump():
    p = sub.Popen(('sudo', 'tcpdump', '-l', '-xx'), stdout=sub.PIPE)
    for row in iter(p.stdout.readline, b''):
        sys.stdout.write(row.rstrip())
def print_hello():
    print "yo"
    time.sleep(20)
    print "goodbye"
def main():
    p1 = multiprocessing.Process(target=tcpdump)
    p2 = multiprocessing.Process(target=print_hello)
    p1.start()
    p2.start()
    while p2.is_alive():
        time.sleep(2)
    p1.terminate()
    print "We terminated"
    #p1.terminate()
    #print "one more time"
    #print_hello()
    #tcpdump()
main()

In python3, its running flawless but in python2 it's giving me an error

tcpdump: Unable to write output: Broken pipe

Can someone know the reason behind this?

PS I changed the print statement before running in python3.

Answer 1

You need to kill the process before leaving the program and remove sudo from the subprocess. This code worked on my machine:

import subprocess as sub
import sys
#import time
import multiprocessing, time, signal


def tcpdump(p):
    for row in iter(p.stdout.readline, b''):
       sys.stdout.write(row.rstrip())
def print_hello():
    print "yo"
    time.sleep(5)
    print "goodbye"
def main():
    p = sub.Popen(('tcpdump', '-l', '-xx'), stdout=sub.PIPE) 
    p1 = multiprocessing.Process(target=tcpdump, args=(p,))
    p2 = multiprocessing.Process(target=print_hello)
    p1.start()
    p2.start()
    while p2.is_alive():
        time.sleep(2)
    p1.terminate()
    p.kill()
    print "We terminated"
    #p1.terminate()
    #print "one more time"
    #print_hello()
    #tcpdump()
main()

Run this script using sudo and everything should be fine.