docs: def transaction(self, txn):
          """Txn processes multiple requests in a single transaction.
  
          A txn request increments the revision of the key-value store and
          generates events with the same revision for every completed request.
          It is not allowed to modify the same key several times within one txn.
  
          :param txn:
          :return:
          """
          return self.post(self.get_url("/kv/txn"),
                           data=json.dumps(txn))