code: def add_hash_memo(self, memo_hash):
          
          memo_hash = memo.HashMemo(memo_hash)
          return self.add_memo(memo_hash)
docs: Set the memo for the transaction to a new :class:`HashMemo
          <stellar_base.memo.HashMemo>`.
  
          :param memo_hash: A 32 byte hash or hex encoded string to use as the memo.
          :type memo_hash: bytes, str
          :return: This builder instance.