<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def receive_request(self, transaction):
 """ Manage the observe option in the request end eventually initialize the client for adding to the list of observers or remove from the list. :type transaction: Transaction :param transaction: the transaction that owns the request :rtype : Transaction :return: the modified transaction """

        if transaction.request.observe == 0:
            # Observe request
            host, port = transaction.request.source
            key_token = hash(str(host) + str(port) + str(transaction.request.token))
            non_counter = 0
            if key_token in self._relations:
                # Renew registration
                allowed = True
            else:
                allowed = False
            self._relations[key_token] = ObserveItem(time.time(), non_counter, allowed, transaction)
        elif transaction.request.observe == 1:
            host, port = transaction.request.source
            key_token = hash(str(host) + str(port) + str(transaction.request.token))
            logger.info("Remove Subscriber")
            try:
                del self._relations[key_token]
            except KeyError:
                pass

        return transaction