code: def validity_duration(self):
          
          if self._proto.HasField('expireMillis'):
              return timedelta(milliseconds=self._proto.expireMillis)
          return None
docs: How long this parameter value is valid.
  
          .. note: There is also an option when subscribing to get updated when
                   the parameter values expire.
  
          :type: :class:`~datetime.timedelta`