test.py

def run(cmd):
  '''Runs a command with subprocess, printing output in realtime'''
  proc = subprocess.Popen(
    cmd,
    stdout=subprocess.PIPE,
    stderr=subprocess.STDOUT
  )
  while proc.poll() is None:
    l = proc.stdout.readline()
    print l,
  print proc.stdout.read()

  cmd = [
    '/Applications/AutoDMG.app/Contents/MacOS/AutoDMG',
    '-L', loglevel,
    'build', templatepath,
    '--download-updates',
    '-o', dmg_output_path]
  print "Full command: %s" % cmd
  run(cmd)