Itertools: `for a in b: for c in b`

Question

I was just looking through the itertools documentation, looking for a way to get rid of a nested for loop like this:

for a in b:
    for c in b:
        <statement>

However, I couldn't find anything. Is there not a function for this? Should I just keep the nested loops?

The original question seems to have been using `for c in b:` in the second line. Several answers seem to apply to that. Maybe if a change of the question changes its meaning so drastically, SO should implement a way of handling this. — Alfe, Oct 28 '13 at 14:01
Rolled back to the original version as it changes the meaning of the question drastically http://meta.stackexchange.com/a/106812/235416 — thefourtheye, Oct 29 '13 at 09:55

score 4 · Answer 1 · answered Oct 28 '13 at 13:12

4

Yes there is. Its called itertools.product

For example:

import itertools

for item in itertools.product([0, 1], repeat = 2):
    print item

Output

(0, 0)
(0, 1)
(1, 0)
(1, 1)

It is equivalent to

b = [0, 1]
for a in b:
    for c in b:
        print (a, c)

answered Oct 28 '13 at 13:12

thefourtheye

Before anyone downvotes this answer, please note that the question was changed! This answer solved the original question correctly. – wheaties Oct 28 '13 at 13:40
@wheaties Thanks man :) But I have to remove this answer now :'( – thefourtheye Oct 28 '13 at 14:04

Games Brainiac · Answer 2 · 2013-10-28T14:01:21.840

4

from itertools import chain

b = [[1, 2, 3], [4, 5, 6]]

for i in chain.from_iterable(b):
    print i

Ideally, b has all the values. So this translates to:

for a in b:
    for c in a:
        print c

Working example. What you're really trying to do is flatten a list, and thats actually included in the recipes for itertools.

edited Oct 28 '13 at 14:01

answered Oct 28 '13 at 13:44

Games Brainiac

Great answer, was about to post this :) – aIKid Oct 28 '13 at 13:48
@GamesBrainiac You rock :) – thefourtheye Oct 28 '13 at 14:08
@GamesBrainiac Please note that I rolled back to the original version as it changes the meaning of the question drastically as per this answer meta.stackoverflow.com/a/106812/235416 – thefourtheye Oct 29 '13 at 11:36
@thefourtheye Thats fine. I'd never downvote any of your questions unless someone threatened me to :P – Games Brainiac Oct 29 '13 at 12:05
@GamesBrainiac Neither do I :) I ll just mention if there is something wrong. – thefourtheye Oct 29 '13 at 12:11

2 Answers2