new_contents: def run_seq(cmd):
      """Run `cmd` and yield its output lazily"""
      p = subprocess.Popen(
          cmd, shell=True,
          stdin=subprocess.PIPE,
          stdout=subprocess.PIPE,
          stderr=subprocess.STDOUT)
  
      # make STDIN and STDOUT non-blocking
      fcntl.fcntl(p.stdin, fcntl.F_SETFL, os.O_NONBLOCK)
      fcntl.fcntl(p.stdout, fcntl.F_SETFL, os.O_NONBLOCK)
  
      p.stdin.close()
  
      while True:
          try:
              chunk = p.stdout.read(32)
              if not chunk:
                  break
              yield chunk
          except IOError:
              ex = sys.exc_info()[1]
              if ex[0] != errno.EAGAIN:
                  raise
              sys.exc_clear()
          socket.wait_read(p.stdout.fileno())
  
      p.stdout.close()
  
subject: Add async execution script