code: def account_data(self, address, key):
          
          endpoint = '/accounts/{account_id}/data/{data_key}'.format(
              account_id=address, data_key=key)
          return self.query(endpoint)
docs: This endpoint represents a single data associated with a given
          account.
  
          `GET /accounts/{account}/data/{key}
          <https://www.stellar.org/developers/horizon/reference/endpoints/data-for-account.html>`_
  
          :param str address: The account ID to look up a data item from.
          :param str key: The name of the key for the data item in question.
          :return: The value of the data field for the given account and data key.
          :rtype: dict