'Return an index key for a given instance. Useful for caching.'

def _get_instance_key(self, host, namespace, wmi_class, other=None):

    if other:
        return '{host}:{namespace}:{wmi_class}-{other}'.format(host=host, namespace=namespace, wmi_class=wmi_class, other=other)
    return '{host}:{namespace}:{wmi_class}'.format(host=host, namespace=namespace, wmi_class=wmi_class)
