Set the memo for the transaction to a new :class:`RetHashMemo
        <stellar_base.memo.RetHashMemo>`.

        :param bytes memo_return: A 32 byte hash or hex encoded string intended to be interpreted as
            the hash of the transaction the sender is refunding.
        :type memo_return: bytes, str
        :return: This builder instance.

def add_ret_hash_memo(self, memo_return):
        """Set the memo for the transaction to a new :class:`RetHashMemo
        <stellar_base.memo.RetHashMemo>`.

        :param bytes memo_return: A 32 byte hash or hex encoded string intended to be interpreted as
            the hash of the transaction the sender is refunding.
        :type memo_return: bytes, str
        :return: This builder instance.

        """
        memo_return = memo.RetHashMemo(memo_return)
        return self.add_memo(memo_return)