Iterating over several lists at once

[Fredrik Lundh]

"Gal Diskin" wrote:

> I am writing a code that needs to iterate over 3 lists at the same
> time, i.e something like this:
>
> for x1 in l1:
>    for x2 in l2:
>        for x3 in l3:
>            print "do something with", x1, x2, x3
>
> What I need to do is go over all n-tuples where the first argument is
> from the first list, the second from the second list, and so on...
>
> I was wondering if one could write this more easily in some manner
> using only 1 for loop.
> What I mean is something like this:
>
> for (x1,x2,x3) in (l1,l2,l3):
>    print "do something with", x1, x2, x3

how about

    for x1, x2, x3 in func(l1, l2, l3):
        print x1, x2, x3

where func is defined as, say,

    def func(l1, l2, l3):
        return ((x1, x2, x3) for x1 in l1 for x2 in l2 for x3 in l3)

or if you prefer

    def helper(l1, l2, l3):
        for x1 in l1:
            for x2 in l2:
                for x3 in l3:
                    yield x1, x2, x3

</F>