def acknowledge(self, project, subscription, ack_ids):
        """
        """
        service = self.get_conn()
        full_subscription = _format_subscription(project, subscription)
        try:
            service.projects().subscriptions().acknowledge(
                subscription=full_subscription, body={'ackIds': ack_ids}
            ).execute(num_retries=self.num_retries)
        except HttpError as e:
            raise PubSubException(
                'Error acknowledging {} messages pulled from subscription {}'
                .format(len(ack_ids), full_subscription), e)