[Python-Dev] PEP 393 Summer of Code Project (original) (raw)

Steven D'Aprano steve at pearwood.info
Sat Aug 27 09:40:24 CEST 2011

Terry Reedy wrote:

On 8/26/2011 8:23 PM, Antoine Pitrou wrote:

I would only agree as long as it wasn't too much worse than O(1). O(log n) might be all right, but O(n) would be unacceptable, I think. It also depends a lot on actual measured performance Amen. Some regard O(n*n) sorts to be, by definition, 'worse' than O(n*logn). I even read that in an otherwise good book by a university professor. Fortunately for Python users, Tim Peters ignored that 'wisdom', coded the best O(n*n) sort he could, and then measured to find out what was better for what types and lengths of arrays. So not we have a list.sort that sometimes beats the pure O(nlog) quicksort of C libraries.

A nice story, but Quicksort's worst case is O(n*n) too.

http://en.wikipedia.org/wiki/Quicksort

timsort is O(n) in the best case (all items already in order).

You are right though about Tim Peters doing extensive measurements:

http://bugs.python.org/file4451/timsort.txt

If you haven't read the whole thing, do so. I am in awe -- not just because he came up with the algorithm, but because of the discipline Tim demonstrated in such detailed testing. A far cry from a couple of timeit runs on short-ish lists.

-- Steven

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