On Mar 23, 10:51 am, Stefan Behnel <stefan...@behnel.de> wrote: > 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.
The original question posted here was, "Is there a use case for cmp?" There is, and your excuse-making doesn't change the fact. It's the most natural way to sort sometimes; that's a use case. We already knew it could be worked around. It's kind of ridiculous to claim that cmp adds much complexity (it's maybe ten lines of extra C code), so the only reason not to include it is that it's much slower than using key. Not including it for that reason would be akin to the special-casing of sum to prevent strings from being concatenated, although omitting cmp would not be as drastic since it's not a special case. Do we omit something that's useful but potentially slow? I say no. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
