[New-bugs-announce] [issue17615] String comparison performance regression

[Neil Hodgson]

New submission from Neil Hodgson:

On Windows, non-equal comparisons (<, <=, >, >=) between strings with common prefixes are slower in Python 3.3 than 3.2. This is for both 32-bit and 64-bit builds. Performance on Linux has not decreased for the same code. The attached program tests comparisons for strings that have common prefixes.

On a 64-bit build, a 25 character string comparison is around 30% slower and a 100 character string averages 85% slower. A user of 32-bit Python builds reported the 25 character case to average 70% slower. 

Here are two runs of the program using 3.2/3.3 on Windows 7 on an i7 870:

>c:\python32\python -u "charwidth.py"
3.2 (r32:88445, Feb 20 2011, 21:30:00) [MSC v.1500 64 bit (AMD64)]
a=['C:/Users/Neil/Documents/b','C:/Users/Neil/Documents/z']176
[0.7116295577956576, 0.7055591343157613, 0.7203483026429418]

a=['C:/Users/Neil/Documents/λ','C:/Users/Neil/Documents/η']176
[0.7664397841378787, 0.7199902325464409, 0.713719289812504]

a=['C:/Users/Neil/Documents/b','C:/Users/Neil/Documents/η']176
[0.7341851791817691, 0.6994205901833599, 0.7106807593741005]

a=['C:/Users/Neil/Documents/𠀀','C:/Users/Neil/Documents/𠀁']180
[0.7346812372666784, 0.6995411113377914, 0.7064768417728411]

>c:\python33\python -u "charwidth.py"
3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:57:17) [MSC v.1600 64 bit (AMD64)]
a=['C:/Users/Neil/Documents/b','C:/Users/Neil/Documents/z']108
[0.9913326076446045, 0.9455845241056282, 0.9459076605341776]

a=['C:/Users/Neil/Documents/λ','C:/Users/Neil/Documents/η']192
[1.0472289217234318, 1.0362342484091207, 1.0197109728048384]

a=['C:/Users/Neil/Documents/b','C:/Users/Neil/Documents/η']192
[1.0439643704533834, 0.9878581050301687, 0.9949265834034335]

a=['C:/Users/Neil/Documents/𠀀','C:/Users/Neil/Documents/𠀁']312
[1.0987483965446412, 1.0130257167690004, 1.024832248526499]

----------
components: Unicode
files: charwidth.py
messages: 185824
nosy: Neil.Hodgson, ezio.melotti
priority: normal
severity: normal
status: open
title: String comparison performance regression
versions: Python 3.3
Added file: http://bugs.python.org/file29652/charwidth.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17615>
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