spawning a process with subprocess

[MonkeeSage]

Hi Brian,

Couple of things. You should use poll() on the Popen instance, and
should check it explicitly against None (since a 0 return code,
meaning exit successfully, will be treated as a false condition the
same as None). Also, in your second example, you block the program
when you call readlines on the pipe, since readlines blocks until it
reaches eof (i.e., until pipe closes stdout, i.e., process is
complete). Oh, and you don't have to split the input to the args
option yourself, you can just pass a string. So, putting it all
together, you want something like:

import subprocess, time

cmd = "cat somefile"
proc = subprocess.Popen(args=cmd, shell=True,
  stdout=subprocess.PIPE, stdin=subprocess.PIPE,
  stderr=subprocess.STDOUT, close_fds=True)

while 1:
  time.sleep(1)
  if proc.poll() != None:
    break
  else:
    print "waiting on child..."

print "returncode =", proc.returncode

HTH,
Jordan