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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def update(self, ttl=values.unset):
 """ Update the SyncStreamInstance :param unicode ttl: Stream TTL. :returns: Updated SyncStreamInstance :rtype: twilio.rest.sync.v1.service.sync_stream.SyncStreamInstance """

        return self._proxy.update(ttl=ttl, )