[Python-ideas] Function to unnest for-statements

[Leif Walsh]

On Fri, 23 May 2008, Leif Walsh wrote:
> I've worked this out (I'm sure I did this in intro CS once before...),
> although there is probably some optimization trick I'm missing, and
> I'm probably doing some silly double-allocation thing or something.
>
> >>> def combine(lists):
> ...     if len(lists) is 0:
> ...             return [[]]
> ...     first = combine(lists[0:-1])
> ...     total = []
> ...     for item in lists[-1]:
> ...             total += [[item] + subset for subset in first]
> ...     return total

Oops, that should probably be:

...     for subset in first:
...             total += [subset + [item] for item in lists[-1]]

to maintain order.  My excuse is that it's past my bedtime.

-- 
Cheers,
Leif