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.

def retention_period(self, value):
        """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.
        """
        policy = self._properties.setdefault("retentionPolicy", {})
        if value is not None:
            policy["retentionPeriod"] = str(value)
        else:
            policy = None
        self._patch_property("retentionPolicy", policy)