code: def retention_period(self, value):
          
          policy = self._properties.setdefault("retentionPolicy", {})
          if value is not None:
              policy["retentionPeriod"] = str(value)
          else:
              policy = None
          self._patch_property("retentionPolicy", policy)
docs: Set the retention period for items in the bucket.
  
          :type value: int
          :param value:
              number of seconds to retain items after upload or release from
              event-based lock.
  
          :raises ValueError: if the bucket's retention policy is locked.