Produce product of lists
The itertools library has a function called product. You can rewrite your snippet as:

global sum_list=itertools.product(list_a, list_b, list_bb) + itertools.product(list_a, list_c, list_cc)


If you don't want to use itertools (e.g. because you're stuck on python 2.4), you can also use a list comprehension:

global sum_list=[]
sum_list.extend([a,b,bb] for a in list_a for b in list_b for bb in list_bb)
sum_list.extend([a,c,cc] for a in list_a for c in list_c for cc in list_cc)