Guido rethinking removal of cmp from sort method

[Stefan Behnel]

Carl Banks, 23.03.2011 18:23:
> On Mar 23, 6:59 am, Stefan Behnel wrote:
>> Antoon Pardon, 23.03.2011 14:53:
>>
>>> On Sun, Mar 13, 2011 at 12:59:55PM +0000, Steven D'Aprano wrote:
>>>> The removal of cmp from the sort method of lists is probably the most
>>>> disliked change in Python 3. On the python-dev mailing list at the
>>>> moment, Guido is considering whether or not it was a mistake.
>>
>>>> If anyone has any use-cases for sorting with a comparison function that
>>>> either can't be written using a key function, or that perform really
>>>> badly when done so, this would be a good time to speak up.
>>
>>> How about a list of tuples where you want them sorted first item in ascending
>>> order en second item in descending order.
>>
>> You can use a stable sort in two steps for that.
>
> How about this one: you have are given an obscure string collating
> function implented in a C library you don't have the source to.
>
> Or how about this: I'm sitting at an interactive session and I have a
> convenient cmp function but no convenient key, and I care more about
> the four minutes it'd take to whip up a clever key function or an
> adapter class than the 0.2 seconds I'd save to on sorting time.

As usual with Python, it's just an import away:

http://docs.python.org/library/functools.html#functools.cmp_to_key

I think this is a rare enough use case to merit an import rather than being 
a language feature.

Stefan