# -*- coding: utf-8 -*-

def combine(x, y):
    return str(x or '') + str(y or '')

def develop(item_lists):
    combs = [None]

    for item_list in item_lists:
        combs = [
            combine(comb, item)
            for comb in combs
            for item in item_list
        ]
        # même chose : (avec "from functools import product")
        # combs = map(combine, product(combs, item_list))

    return combs

assert develop([['AAA','BBB','CCC'],['XXX','YYY'],['000','111']]) == \
    ['AAAXXX000',
     'AAAXXX111',
     'AAAYYY000',
     'AAAYYY111',
     'BBBXXX000',
     'BBBXXX111',
     'BBBYYY000',
     'BBBYYY111',
     'CCCXXX000',
     'CCCXXX111',
     'CCCYYY000',
     'CCCYYY111']