On Thu, 01 Nov 2012 11:53:06 +1100, Chris Angelico wrote: > On Thu, Nov 1, 2012 at 10:44 AM, Steven D'Aprano > <steve+comp.lang.pyt...@pearwood.info> wrote: >> On the contrary. If you are using cmp with sort, your sorts are slow, >> and you should upgrade to using a key function as soon as possible. >> >> > But cmp_to_key doesn't actually improve anything. So I'm not sure how > Py3 has achieved anything; Py2 supported key-based sorting already.
Yes, but there is a lot of old code pre-dating key-based sorts. There's also some examples of code where it isn't obvious how to write it as a key-based sort, but a comparison function is simple. And people coming from other languages that only support comparison-based sorts (C?) will probably continue with what they know. Even though key-based sorting is better, there's a lot of comparison sorting that falls under "if it ain't broke, don't fix it". So even though key-based sorts are better, there are still comparison- based sorts in the wild. Python 2 has to support them. Python 3, which is allowed to break backwards compatibility, does not. So when porting to 3, you have to change the sorts. Most of the time it is simple to convert a comparison-based sort to a key- based sort. For the cases where you either can't come up with a good key function yourself, or were you want to do so mechanically, Python provides cmp_to_key. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
