Run a subprocess and output stdout in a non-blocking fasion

non-blocking_stdout_stream.py

import subprocess
import threading

def _print_stdout(process):
  '''
  Print out the stream line by line. If line is empty we know that the process has finished and we exit
  '''
  while True:
    try:
      line = process.stdout.readline()
    except:
      break
    else:
      if line:
        print line.strip()
      else:
        break

def run(cmd):
  process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, bufsize=1) # redirecting stderr is optional
  # we create a separate process for printing to prevent blocking
  thread = threading.Thread(target=_print_stdout, args=[process])
  thread.daemon = True
  thread.start()
  process.wait()
  
if __name__ == '__main__':
  cmd = ['ls', '-l']
  run(cmd)