generate seqs

def recur(combs, ar):
    res = []
    for comb in combs:
        for x in ar:
            res.append(comb + [x])
    return res

def gen_combs(ars):
    combs = [[]]
    for ar in ars:
        combs = recur(combs, ar)
    return combs

def no_recur(ars):
    combs = [[]]
    for ar in ars:
        new_combs = []
        for comb in combs:
            for x in ar:
                new_combs.append(comb + [x])
        combs = new_combs
    return combs

ars = [[1, 2, 3], [10, 20], [100, 200, 300]]
print(gen_combs(ars))