Reverse zip() ?

[Zac Burns]

More succinct failure:

keys, values = zip(*{}.iteritems())

--
Zachary Burns
(407)590-4814
Aim - Zac256FL
Production Engineer (Digital Overlord)
Zindagi Games



On Tue, Dec 2, 2008 at 4:47 PM, Zac Burns <zac256 at gmail.com> wrote:
> There is a problem with this however, which prompted me to actually
> write an unzip function.
>
> One might expect to be able to do something like so (pseudocode)...
>
> def filesAndAttributes():
>   files = walk()
>   attributes = [attr(f) for f in files]
>   return zip(files, attributes)
>
> files, attributes = zip(*filesAndAttributes())
>
> The corner case is when dealing with empty lists and there aren't
> enough items to unpack.
>
> The unzip function therefore has an elementsForEmpty keyword that
> handles this case. Perhaps something like this could be added to zip?
> I have not (yet) dealt with the PEP process, so I'm not sure where
> that starts. Perhaps a discussion could start here.
>
> --
> Zachary Burns
> (407)590-4814
> Aim - Zac256FL
> Production Engineer (Digital Overlord)
> Zindagi Games
>
>
>
> On Tue, Dec 2, 2008 at 4:14 PM, John Machin <sjmachin at lexicon.net> wrote:
>> On Dec 3, 7:12 am, Stefan Behnel <stefan... at behnel.de> wrote:
>>> Andreas Waldenburger wrote:
>>> > we all know about the zip builtin that combines several iterables into
>>> > a list of tuples.
>>>
>>> > I often find myself doing the reverse, splitting a list of tuples into
>>> > several lists, each corresponding to a certain element of each tuple
>>> > (e.g. matplotlib/pyplot needs those, rather than lists of points).
>>>
>>> > This is of course trivial to do via iteration or listcomps, BUT, I was
>>> > wondering if there is a function I don't know about that does this
>>> > nicely?
>>>
>>> I think you're asking about zip():
>>>
>>>         >>> l=[1,2,3]
>>>         >>> zip(l,l)
>>>         [(1, 1), (2, 2), (3, 3)]
>>>         >>> zip(*zip(l,l))
>>>         [(1, 2, 3), (1, 2, 3)]
>>>
>>
>> Here's a version that makes it slightly easier to comprehend:
>>
>> Q: I know how to zip sequences together:
>> | >>> a = (1, 2, 3)
>> | >>> b = (4, 5, 6)
>> | >>> z = zip(a, b)
>> | >>> z
>> | [(1, 4), (2, 5), (3, 6)]
>> but how do I reverse the process?
>>
>> A: Use zip()!
>> | >>> a2, b2 = zip(*z)
>> | >>> a2
>> | (1, 2, 3)
>> | >>> b2
>> | (4, 5, 6)
>>
>> Cheers,
>> John
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>