'Return the modification time of the file storing the session\'s content.'

def _last_modification(self):

    modification = os.stat(self._key_to_file()).st_mtime
    if settings.USE_TZ:
        modification = datetime.datetime.utcfromtimestamp(modification)
        modification = modification.replace(tzinfo=timezone.utc)
    else:
        modification = datetime.datetime.fromtimestamp(modification)
    return modification
