code: def append_payment_op(self,
                            destination,
                            amount,
                            asset_code='XLM',
                            asset_issuer=None,
                            source=None):
          
          asset = Asset(code=asset_code, issuer=asset_issuer)
          op = operation.Payment(destination, asset, amount, source)
          return self.append_op(op)
docs: Append a :class:`Payment <stellar_base.operation.Payment>` operation
          to the list of operations.
  
          :param str destination: Account address that receives the payment.
          :param str amount: The amount of the currency to send in the payment.
          :param str asset_code: The asset code for the asset to send.
          :param asset_issuer: The address of the issuer of the asset.
          :type asset_issuer: str, None
          :param str source: The source address of the payment.
          :return: This builder instance.