How can I find all the possible combinations of a list of lists (in Python)?

Question

I have the following structure in Python:

letters = [['a', 'b', 'c'], ['p', 'q', 'r', 's'], ['j', 'k', 'l']]

I would like to find all the possible combinations of letters in the order that they currently exist. For the example above this would be:

apj
apk
apl
aqj
aqk
aql
...
csk
csl

This seems like it should be a very simple thing to do but I cannot figure it out.

Can we assume that the values are already ordered within the individual lists? — wcm, Jun 07 '10 at 13:49
@wcm: No, the values in the individual lists are not ordered. — Peter Horne, Jun 07 '10 at 13:54
Seems to be a duplicate of http://stackoverflow.com/questions/2990003/how-can-i-find-all-the-possible-combinations-of-a-list-of-lists-in-python — Tamás, Jun 07 '10 at 13:55
whoops, wrong link, I meant this one: http://stackoverflow.com/questions/533905/get-the-cartesian-product-of-a-series-of-lists-in-python — Tamás, Jun 07 '10 at 16:03

score 14 · Accepted Answer · answered Jun 07 '10 at 13:48

14

In Python 2.6 or newer you can use itertools.product:

>>> import itertools
>>> map(''.join, itertools.product(*letters))
apj
apk
apl
aqj
aqk
aql
...etc...
csk
csl

answered Jun 07 '10 at 13:48

Mark Byers

And in older Pythons, you can copy the pure Python implementation of `product` from the `itertools` docs. – Mike Graham Jun 07 '10 at 14:07

1 Answers1