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
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