def actor_key(name, namespace):
    """
    generate the key used to key the actor in memory bases
    on the actor path and namespace used


    :param name: name of the actor
    :type name: str
    :param namespace: 0-db namespace used by this actor
    :type namespace: str
    :return: key used to keep the actor in memory
    :rtype: str
    """
    return "%s__%s" % (namespace, name)