code: def transfer_assets(self, asset_id, transfer_spec, btc_change_script, fees):
          
          return self.transfer(
              [(asset_id, transfer_spec)],
              TransferParameters(transfer_spec.unspent_outputs, None, btc_change_script, 0),
              fees)
docs: Creates a transaction for sending an asset.
  
          :param bytes asset_id: The ID of the asset being sent.
          :param TransferParameters transfer_spec: The parameters of the asset being transferred.
          :param bytes btc_change_script: The script where to send bitcoin change, if any.
          :param int fees: The fees to include in the transaction.
          :return: The resulting unsigned transaction.
          :rtype: CTransaction