Output and merge subprocess outputs

child.py

#!/usr/bin/env python

from time import sleep

for i in range(1, 3):
    print "line %d" %(i, )
    print "xxxxxxxxxx" * 20
    sleep(5)

print "exit"

parent.py

#!/usr/bin/env python

from subprocess import Popen, PIPE
from time import sleep
import sys
from Queue import Queue, Empty
from threading import Thread

def enqueue_output(out, queue):
    for line in iter(out.readline, b''):
        queue.put(line)
    out.close()

p = Popen(['/public/bin/python', 'child.py'], stdout=PIPE, bufsize=1)
q = Queue()
t = Thread(target=enqueue_output, args=(p.stdout, q))
t.daemon = True
t.start()

stdout_buf = []
retcode = None

while True:
    try:
        line = q.get_nowait()
    except Empty:
        if retcode is not None:
            # process exited and no more lines to process
            break
        else:
            # wait a little while
            sleep(1)
    else:
        sys.stdout.write(line)
        stdout_buf += line
        # simulate line processing 
        sleep(10)
    retcode = p.poll()

print 'child exited with code: %d' % (retcode,)

all_stdout = ''.join(stdout_buf)