Compares the timestamps of file *src* and *dst*, returning #True if the
  *dst* is out of date or does not exist. Raises an #OSError if the *src*
  file does not exist.

def compare_timestamp(src, dst):
  """
  Compares the timestamps of file *src* and *dst*, returning #True if the
  *dst* is out of date or does not exist. Raises an #OSError if the *src*
  file does not exist.
  """

  try:
    dst_time = os.path.getmtime(dst)
  except OSError as exc:
    if exc.errno == errno.ENOENT:
      return True  # dst does not exist

  src_time = os.path.getmtime(src)
  return src_time > dst_time