Walk two lists (no zip)

Question

This is my implementation:

def walk_two(a, b):
    for x in a:
        for y in b:
            yield x, y

a = xrange(2)
b = xrange(3)

for x, y in walk_two(a, b):
    print x, y

With this output:

Is there a better (more pythonic) way of doing that? A built-in? A more generic walkN?

score 7 · Accepted Answer · answered Aug 08 '14 at 07:53

7

You are looking for itertools.product:

from itertools import product
a = xrange(2)
b = xrange(3)

for x, y in product(a, b):
    print x, y

answered Aug 08 '14 at 07:53

Daniel

42,087
4
55
81

score 3 · Answer 2 · answered Aug 08 '14 at 07:53

itertools.product does what you want and is extensible to more lists:

https://docs.python.org/2/library/itertools.html#itertools.product

import itertools
a = xrange(2)
b = xrange(3)

for x, y in itertools.product(a, b):
    print x, y

Output:

score 1 · Answer 3 · answered Aug 08 '14 at 07:53

1

Have a look at itertools.product.

answered Aug 08 '14 at 07:53

Antoine

1,070
7
11

1

This is a link-only answer, which are strogly discouraged. Please add at least an example. – J0HN Aug 08 '14 at 07:53
At least, we all agree ;) – Antoine Aug 08 '14 at 07:56

score 0 · Answer 4 · answered Aug 08 '14 at 07:55

0

I think this one is slightly better:

>>> for a in xrange(2):
...   for b in xrange(3):
...     print a, b
... 
0 0
0 1
0 2
1 0
1 1
1 2

You don't need to use the generator here, as you are using the xrange() function. The function returns xrange object instead of a list.

>>> a = xrange(10)
>>> a
xrange(10)
>>>

answered Aug 08 '14 at 07:55

Tamim Shahriar

739
4
9

Not the more pythonic but this code is the fastest one. – xbello Aug 08 '14 at 08:11
In my case, performance is not a worry, readability is. Having a single loop instead of two, improves readability drastically. Having a single loop instead of N (for the general case), makes wonders for readability. – blueFast Aug 08 '14 at 08:14
@jeckyll2hide, this answer was being downvoted. Yeah, it's awful to nest many *for loops*, but if someone stumbles into this question with only two lists to iterate and performance is a worry... use this solution! No need to downvote. – xbello Aug 08 '14 at 15:10
@xbello: I didn't downvote, but I should have. The answer here is the same as the code in my question. – blueFast Aug 09 '14 at 08:30
The answer here is not exactly the same as in your question. You didn't need to use the walk_two method. Is it unnecessary here. – Tamim Shahriar Aug 09 '14 at 16:45

Walk two lists (no zip)

4 Answers4