def index_natsorted(seq, key=None, reverse=False, alg=ns.DEFAULT):
    if key is None:
        newkey = itemgetter(1)
    else:
        def newkey(x):
            return key(itemgetter(1)(x))
    index_seq_pair = [[x, y] for x, y in enumerate(seq)]
    index_seq_pair.sort(reverse=reverse, key=natsort_keygen(newkey, alg))
    return [x for x, _ in index_seq_pair]