def terminate_instances(self, xml_bytes):
        """Parse the XML returned by the C{TerminateInstances} function.

        @param xml_bytes: XML bytes with a C{TerminateInstancesResponse} root
            element.
        @return: An iterable of C{tuple} of (instanceId, previousState,
            currentState) for the ec2 instances that where terminated.
        """
        root = XML(xml_bytes)
        result = []
        # May be a more elegant way to do this:
        instances = root.find("instancesSet")
        if instances is not None:
            for instance in instances:
                instanceId = instance.findtext("instanceId")
                previousState = instance.find("previousState").findtext(
                    "name")
                currentState = instance.find("currentState").findtext(
                    "name")
                result.append((instanceId, previousState, currentState))
        return result
Parse the XML returned by the C{TerminateInstances} function.

        @param xml_bytes: XML bytes with a C{TerminateInstancesResponse} root
            element.
        @return: An iterable of C{tuple} of (instanceId, previousState,
            currentState) for the ec2 instances that where terminated.