New submission from Xiang Zhang:
I make a try to improve str.count one character for latin1 string. From
benchmark, it could enhance the speed depending on the length of the string.
# short one, a little regression
./python3 -m perf timeit --compare-to ~/cpython/python -s 's="abcdefg"'
's.count("a")'
python: ..................... 190 ns +- 1 ns
python3: ..................... 197 ns +- 2 ns
Median +- std dev: [python] 190 ns +- 1 ns -> [python3] 197 ns +- 2 ns: 1.04x
slower
# a little longer
./python3 -m perf timeit --compare-to ~/cpython/python -s 's="abcdefghi"'
's.count("a")'
python: ..................... 192 ns +- 15 ns
python3: ..................... 184 ns +- 2 ns
Median +- std dev: [python] 192 ns +- 15 ns -> [python3] 184 ns +- 2 ns: 1.05x
faster
# longer
./python3 -m perf timeit --compare-to ~/cpython/python -s
's="abcdefghihijklmnopqrstuvwxyz~!@##$%^&*()-=_+{}|"' 's.count("a")'
python: ..................... 236 ns +- 12 ns
python3: ..................... 209 ns +- 9 ns
Median +- std dev: [python] 236 ns +- 12 ns -> [python3] 209 ns +- 9 ns: 1.13x
faster
# very long
./python3 -m perf timeit --compare-to ~/cpython/python -s 's="abcdefgHijk"*100'
's.count("z")'
python: ..................... 1.02 us +- 0.00 us
python3: ..................... 610 ns +- 1 ns
Median +- std dev: [python] 1.02 us +- 0.00 us -> [python3] 610 ns +- 1 ns:
1.67x faster
And since str.replace may also go through the code path involving count, it's
somewhat affected:
./python3 -m perf timeit --compare-to ~/cpython/python -s
's="abcdefghihijklmnopqrstuvwxyz~!@##$%^&*()-=_+{}|"' 's.replace("a", "ccc")'
python: ..................... 318 ns +- 31 ns
python3: ..................... 298 ns +- 19 ns
Median +- std dev: [python] 318 ns +- 31 ns -> [python3] 298 ns +- 19 ns: 1.07x
faster
For ucs2 and ucs4, the benchmarks are not appealing so leave them untouched.
----------
components: Interpreter Core
files: latin1-str-count-one-character.patch
keywords: patch
messages: 282784
nosy: haypo, serhiy.storchaka, xiang.zhang
priority: normal
severity: normal
stage: patch review
status: open
title: Make str.count one character for latin1 string faster
type: enhancement
versions: Python 3.7
Added file:
http://bugs.python.org/file45816/latin1-str-count-one-character.patch
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<http://bugs.python.org/issue28921>
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