def list_by_instance(self, instance_id):
        """Gets security groups of an instance.

        :returns: List of SecurityGroup objects associated with the instance
        """
        ports = port_list(self.request, device_id=instance_id)
        sg_ids = []
        for p in ports:
            sg_ids += p.security_groups
        return self._list(id=set(sg_ids)) if sg_ids else []
Gets security groups of an instance.

        :returns: List of SecurityGroup objects associated with the instance