(newbie) N-uples from list of lists

[bonono at gmail.com]

Out of curiousity, is "recursion" the desirable way(or is it pythonic
way) ? How would one do it in the imperative way ?

Dan Bishop wrote:
> > it could be done by a recursive call, but i am interested in using and
> > understanding generators.
>
> def cross(*args):
>    """Iterates over the set cross product of args."""
>    if not args:
>       return
>    elif len(args) == 1:
>       for x in args[0]:
>          yield (x,)
>    else:
>       for x in args[0]:
>          for y in cross(*args[1:]):
>             yield (x,) + y
>
> >>> cross(['a0', 'a1', 'a2'], ['b0', 'b1'], ['c0', 'c1', 'c2', 'c3'])
> <generator object at 0xb7df072c>
> >>> list(_)
> [('a0', 'b0', 'c0'), ('a0', 'b0', 'c1'), ('a0', 'b0', 'c2'), ('a0',
> 'b0', 'c3'), ('a0', 'b1', 'c0'), ('a0', 'b1', 'c1'), ('a0', 'b1',
> 'c2'), ('a0', 'b1', 'c3'), ('a1', 'b0', 'c0'), ('a1', 'b0', 'c1'),
> ('a1', 'b0', 'c2'), ('a1', 'b0', 'c3'), ('a1', 'b1', 'c0'), ('a1',
> 'b1', 'c1'), ('a1', 'b1', 'c2'), ('a1', 'b1', 'c3'), ('a2', 'b0',
> 'c0'), ('a2', 'b0', 'c1'), ('a2', 'b0', 'c2'), ('a2', 'b0', 'c3'),
> ('a2', 'b1', 'c0'), ('a2', 'b1', 'c1'), ('a2', 'b1', 'c2'), ('a2',
> 'b1', 'c3')]