code: def append_pre_auth_tx_signer(self,
                                    pre_auth_tx,
                                    signer_weight,
                                    source=None):
          
          return self.append_set_options_op(
              signer_address=pre_auth_tx,
              signer_type='preAuthTx',
              signer_weight=signer_weight,
              source=source)
docs: 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.