docs: def get_app_settings(parser, known_args):
      """
      Return **settings** module of the application according to
      either command line argument or **SHELTER_SETTINGS_MODULE**
      environment variable.
      """
      args, dummy_remaining = parser.parse_known_args(known_args)
      settings_module_path = (
          args.settings or os.environ.get('SHELTER_SETTINGS_MODULE', ''))
      if not settings_module_path:
          return None
      return importlib.import_module(settings_module_path)