How do I loop through a tuple of lists element-wise?

Question

I have a function that returns a tuple of two lists

def two_lists():
    return [1, 2, 3], ['a', 'b', 'c']

I want to loop through the tuple in a manner similar to this

for v1, v2 in two_lists():
   print v1, v2

output:
    1, a
    2, b
    3, c

The only way I have found I find rather cumbersome!

a, b = two_lists()
for i, y in zip(a, b):
    print i, y

Is there a prettier more pythonic way to achieve this?

If you want to make it terser, you can just do `for i, y in zip(*two_lists())`, which will upack the tuple in-place. Otherwise, if you're trying to say `zip` is un-pythonic, I would disagree. — user3030010, Oct 06 '16 at 18:57
Please, please, please do not use list comprehensions for their side effects. It's incredibly bad practice and inefficient. There is never a time when that is the correct solution. — Morgan Thrapp, Oct 06 '16 at 19:26
So, having a resulting list with `[None, None, None, None]` is OK? That doesn't seem like the best advice here. I would advise against using that list comp solution. — idjaw, Oct 06 '16 at 19:28
Another nice python 3 way of doing it (Python 3.5 or higher only), which should satisfy all the above complaints: `print( *((i,y) for i,y in zip(*twolists()), sep = '\n')` — Rick, Oct 06 '16 at 19:33
@MorganThrapp I was happy to see multiple unpacking functionality added to 3.5 precisely because of this complaint. There *should* have been a nice way to do a print-type operation in one line, but there wasn't. Now, there is. — Rick, Oct 06 '16 at 19:37
hmm @RickTeachey You have unbalanced parentheses and the output seems to be -> `(1, 'a')\n(2, 'b')\n(3, 'c')` — idjaw, Oct 06 '16 at 19:49
@idjaw Whoops! Here it is corrected: `print( *((i,y) for i,y in zip(*twolists())), sep = '\n')`. That's equivalent to the required output. — Rick, Oct 06 '16 at 20:01

score 7 · Accepted Answer · answered Oct 06 '16 at 18:57

7

Sure, you can directly unpack two_lists() in your zip call.

for i, y in zip(*two_lists()):
    print i, y

This is the idiomatic way to do this.

answered Oct 06 '16 at 18:57

Morgan Thrapp

1 Answers1