de_bruijn_iterative.py

def db(word_size, alphabet_size):
    L1 = alphabet_size**(word_size-1)
    lookup_table = {}
    i = 0
    for _ in range(L1*alphabet_size):
        if i not in lookup_table:
            lookup_table[i] = alphabet_size - 1
        
        s = lookup_table[i]
        yield alphabet_size - s - 1
        if s != 0:
            lookup_table[i] = s - 1
        else:
            lookup_table.pop(i)

        i = (i * alphabet_size + s) % L1

    for _ in range(word_size-1):
        yield 0

the lookup table is at most about alphabet_size times smaller than L1 and it's maximum range is roughly the same