import random

# Package must be installed.
from nds import ndomsort

seq = [random.sample(range(-10, 11), 5) for i in range(30)]

# It is dictionary.
fronts = ndomsort.non_domin_sort(seq)

# Or we can get values of objectives.
# fronts = ndomsort.non_domin_sort(seq, lambda x: x[:4])

# 'fronts' is a tuple of front's indices, not a dictionary.
# fronts = ndomsort.non_domin_sort(seq, only_front_indices=True)

for front in fronts:
    print("\nFront index is {}".format(front))
    for seq in fronts[front]:
        print("\t{}".format(seq))