Guido rethinking removal of cmp from sort method

[Steven D'Aprano]

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