On Fri, 25 Mar 2011 10:21:35 +0100, Antoon Pardon wrote: > On Thu, Mar 24, 2011 at 11:49:53PM +0000, Steven D'Aprano wrote: >> On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote: >> >> > However since that seems to be a problem for you I will be more >> > detailed. The original poster didn't ask for cases in which cmp was >> > necessary, he asked for cases in which not using cmp was cumbersome. >> >> I'm the original poster, and that's not what I said. I said: >> >> "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." >> >> You'll notice that I said nothing about whether writing the code was >> easy or cumbersome, and nothing about readability. > > Well fine. I should have realised the question was just a pretense and > that there really never was any intention to consider the reactions, > because the answer is already fixed. Of course a key function can always > be written, it may just need a specific class to implement the specific > order. Likewise there is no reason to expect the order-functions to > preform worse when implemented in a class, rather than in a function.
The reason Guido is considering re-introducing cmp is that somebody at Google approached him with a use-case where a key-based sort did not work. The use-case was that the user had masses of data, too much data for the added overhead of Decorate-Sort-Undecorate (which is what key does), but didn't care if it took a day or two to sort. So there is at least one use-case for preferring slowly sorting with a comparison function over key-based sorting. I asked if there any others. It seems not. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
