code: def directory(self, dir_key):
      '''Initializes directory at dir_key.'''
      dir_items = self.get(dir_key)
      if not isinstance(dir_items, list):
        self.put(dir_key, []f directory(self, dir_key):
      '''Initializes directory at dir_key.'''
      dir_items = self.get(dir_key)
      if not isinstance(dir_items, list):
        self.put(dir_key, [])
docs: Initializes directory at dir_key.