code: def listdir(store, path=None):
      
      path = normalize_storage_path(path)
      if hasattr(store, 'listdir'):
          # pass through
          return store.listdir(path)
      else:
          # slow version, iterate through all keys
          return _listdir_from_keys(store, path)
docs: Obtain a directory listing for the given path. If `store` provides a `listdir`
      method, this will be called, otherwise will fall back to implementation via the
      `MutableMapping` interface.