python 3's adoption

Steven D'Aprano steven at REMOVE.THIS.cybersource.com.au
Thu Jan 28 02:56:00 CET 2010


On Wed, 27 Jan 2010 16:44:18 -0800, Carl Banks wrote:

>> You're referring to the O(N**2) bit, right? I am sure he knew it was O
>> (N*log(N)), which is still worse than O(N) for key.
>>
>> If he didn't, well, Python has some fundamental flaws in its basic sort
>> algorithm.
> 
> Quicksort is O(N**2) worst case, perhaps that's what he meant.

No, apparently I was delusional.


> I'm not
> sure about timsort but since it's based on quicksort I'd guess it is
> O(N**2) or worse, worst case, as well.

timsort is actually a mergesort, not a quicksort.

You may like to read this:

http://svn.python.org/projects/python/trunk/Objects/listsort.txt


> Typical case of a sort is still O(N*log(N)) whether using key or cmp.
> People recommended against cmp not because of overall algorithmic time
> considerations, but because of the number of function calls.  cmp
> function was called a minimum of N-1 times and typically around N*log2
> (N) times, whereas key was called exactly N times.  Since the overhead
> of a Python function call was very large compared to the built-in cmp
> operation, it usually outweighed the algorithmic time considerations.

Yes, that sounds more like it. Thanks for the corrections.


-- 
Steven



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