Add a PreAuthTx signer to an account.

        Add a PreAuthTx signer to an account via a :class:`SetOptions
        <stellar_base.operation.SetOptions` operation. This is a helper
        function for :meth:`append_set_options_op`.

        :param pre_auth_tx: The address of the new preAuthTx signer - obtained by calling `hash_meta` on the TransactionEnvelope.
        :type pre_auth_tx: str, bytes
        :param int signer_weight: The weight of the new signer.
        :param str source: The source account that is adding a signer to its
            list of signers.
        :return: This builder instance.

def append_pre_auth_tx_signer(self,
                                  pre_auth_tx,
                                  signer_weight,
                                  source=None):
        """Add a PreAuthTx signer to an account.

        Add a PreAuthTx signer to an account via a :class:`SetOptions
        <stellar_base.operation.SetOptions` operation. This is a helper
        function for :meth:`append_set_options_op`.

        :param pre_auth_tx: The address of the new preAuthTx signer - obtained by calling `hash_meta` on the TransactionEnvelope.
        :type pre_auth_tx: str, bytes
        :param int signer_weight: The weight of the new signer.
        :param str source: The source account that is adding a signer to its
            list of signers.
        :return: This builder instance.

        """
        return self.append_set_options_op(
            signer_address=pre_auth_tx,
            signer_type='preAuthTx',
            signer_weight=signer_weight,
            source=source)