Produce product of lists

Question

I want to combine elements in different lists. For example, here are 3 lists.

list_a : [ 1,2,3 ]
list_b : [ 4,5,6 ]
list_c : [ 7,8 ]

Selecting elements from list_b and list_c is mutually exclusive. When including an element from list_b, I'd like to also include an element from list_bb; when including an element from list_c, I'd like to also include an element from list_cc.

list_bb : [ 14,15,16 ]
list_cc : [ 17,18 ]

I wrote this code:

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

Is there any better way to get the same result?

Answer 1

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)