Popen stdout reading pipe, deadlock using sleep

Question

Well, I have two scripts. The a.py which prints the output of the b.py script as follows:

#a.py
from subprocess import Popen, PIPE, STDOUT

p = Popen(['/Users/damian/Desktop/b.py'], shell=False, stdout=PIPE, stderr=STDOUT)

while p.poll() is None:
    print p.stdout.readline()


#b.py
#!/usr/bin/env python
import time

while 1:
    print 'some output'
    #time.sleep(1)

This works.But, Why do my scripts deadlock when I uncomment the time.sleep() line?

Answer 1

Your output is probably buffered. Add a .flush() for stdout to clear it:

import sys
import time

while 1:
    print 'someoutput'
    sys.stdout.flush()
    time.sleep(1)