nesting to a dynamic depth in Python

Question

I have a problem I'm trying to solve which requires nesting as many levels deep as there are items in a list. Or to be precise, iterables in a list.

def example(arg_list):
for i in arg_list[0]:
    for j in arg_list[1]:
        for k in arg_list[2]:
            print "{} {} {}".format(i,j,k)

The above function would run fine as long as the "arg_list" is a list containing 3 iterables, such as [[1,3,4],[4,5,6], [9,3,2,1,0]]. If there were always four iterables in the list, that would be easy to do as well. I need to figure out how to create a function that will add another nested level for each iterable added to the "arg_list" parameter. It seems that recursion might be the way to go, but haven't been able to figure that out.

Is it possible for a list to contain mixed types? For example, `[1,2,[1,2,3]]` ? — rafaelc, Dec 22 '15 at 01:34
Possible duplicate of [Cartesian product of a dictionary of lists](http://stackoverflow.com/questions/5228158/cartesian-product-of-a-dictionary-of-lists) — LinkBerest, Dec 22 '15 at 01:37

kindall · Answer 1 · 2015-12-22T20:09:10.273

7

What you are looking for is called a Cartesian product. Python's itertools module has a function that will do that for you.

from itertools import product

def example(arg_list):
    for items in product(*arg_list):
        print " ".join(str(item) for item in items)

edited Dec 22 '15 at 20:09

answered Dec 22 '15 at 01:35

kindall

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this works, i should have checked itertools. Small edit, since product was imported by itself, it should read "for items in product(*arg_list):... no need to say "...in itertools.product..." – Bennie Dec 22 '15 at 18:35

score 0 · Accepted Answer · answered Dec 22 '15 at 01:37

0

You could use recursion, something like:

def example(arg_list, res=[]):
    if arg_list == []:
        print res
        return
    for i in arg_list[0]:
        example(arg_list[1:], res+[i])

answered Dec 22 '15 at 01:37

Julien

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nesting to a dynamic depth in Python

2 Answers2