<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def encode(self, transmission):
 """ Encodes the data, creating a CWR structure from an instance from the domain model. :param entity: the instance to encode :return: a cwr string structure created from the received data """

        data = ''
        data += self._record_encode(transmission.header)
        for group in transmission.groups:
            data += self._record_encode(group.group_header)
            for transaction in group.transactions:
                for record in transaction:
                    data += self._record_encode(record)
            data += self._record_encode(group.group_trailer)
        data += self._record_encode(transmission.trailer)
        return data