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[Python-Dev] Should standard library modules optimize forCPython?
Stefan Behnelstefan_ml at behnel.de
Sun Jun 1 11:02:56 CEST 2014
Steven D'Aprano, 01.06.2014 10:11:> Briefly, I have a choice of algorithm for the median function in the> statistics module. If I target CPython, I will use a naive but simple> O(N log N) implementation based on sorting the list and returning the> middle item. (That's what the module currently does.) But if I target> PyPy, I will use an O(N) algorithm which knocks the socks off the naive> version even for smaller lists. In CPython that's typically 2-5 times> slower; in PyPy it's typically 3-8 times faster, and the bigger the data> set the more the advantage.>> For the specific details, seehttp://bugs.python.org/issue21592>> My feeling is that the CPython standard library should be written for> CPython, that is, it should stick to the current naive implementation of> median, and if PyPy wants to speed the function up, they can provide> their own version of the module.Note that if you compile the module with Cython, CPython heavily benefitsfrom the new implementation, too, by a factor of 2-5x. So there isn'treally a reason to choose between two implementations because of the tworuntimes, just use the new one for both and compile it for CPython. I addedthe necessary bits to the ticket.Stefan
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