code: def retention_period(self):
          
          policy = self._properties.get("retentionPolicy")
          if policy is not None:
              period = policy.get("retentionPeriod")
              if period is not None:
                  return int(period)
docs: Retrieve or set the retention period for items in the bucket.
  
          :rtype: int or ``NoneType``
          :returns: number of seconds to retain items after upload or release
                    from event-based lock, or ``None`` if the property is not
                    set locally.