code: def tokenstore_factory(registry, database=None):
      
      database = database or 'mongodb'
      if database == 'mongodb':
          db = _mongodb(registry)
          store = MongodbTokenStore(db.tokens)
      else:
          store = MemoryTokenStore()
      return store
docs: Creates a token store with the interface of :class:`twitcher.store.AccessTokenStore`.
      By default the mongodb implementation will be used.
  
      :param database: A string with the store implementation name: "mongodb" or "memory".
      :return: An instance of :class:`twitcher.store.AccessTokenStore`.