为了学习如何创建 C 扩展,我决定只复制一个内置的 .c
文件(在本例中为 itertoolsmodule.c
)并将其放入我的包中。我只是将模块内的名称从 itertools
更改为 mypkg
。
然后我将它(Windows 10、MSVC 社区 14)编译为 setuptools.Extension
:
from setuptools import setup, Extension
itertools_module = Extension('mypkg.itertoolscopy',
sources=['src/itertoolsmodulecopy.c'])
setup(...
ext_modules=[itertools_module])
默认使用编译器标志 /c/nologo/Ox/W3/GL/DNDEBUG/MD
我在某处读到这些默认值等于 python 编译方式的设置。但是我使用 conda(64 位设置)所以这可能不一定是真的。
一切顺利 - 但 filterfalse
的基准测试表明它比内置的快了将近 2 倍:
import mypkg
import itertools
import random
a = [random.random() for _ in range(500000)]
func = None
%timeit list(filter(func, a))
100 loops, best of 3: 3.42 ms per loop
%timeit list(itertools.filterfalse(func, a))
100 loops, best of 3: 3.41 ms per loop
%timeit list(mypkg.filterfalse(func, a))
100 loops, best of 3: 6.77 ms per loop
然而,对于较小的可迭代对象,差异也会变小:
a = [random.random() for _ in range(500)] # 1 / 1000 of the elements
%timeit list(filter(func, a))
100000 loops, best of 3: 9.66 µs per loop
%timeit list(itertools.filterfalse(func, a))
100000 loops, best of 3: 10.8 µs per loop
%timeit list(mypkg.filterfalse(func, a))
100000 loops, best of 3: 14.4 µs per loop
我无法解释这种速度上的差异,但我不得不承认我对编译 C
代码不太熟悉。我不知道实际上是什么让它变慢了。
在带有 ifilter
和 ifilterfalse
的 python 2.7 以及 itertoolsmodule.c
文件的 2.7 版本上,结果是相同的。
有谁知道是什么让代码的性能比内置代码差,以及如何加快它的速度?
最佳答案
出于对这个问题的好奇,我开始尝试重现这些发现。虽然 OP 在 Windows 上,但在 Linux 上尝试这个对我来说稍微容易一些。我最终确实在 Windows 上尝试过它,但我将向您介绍我所做的一切!
设置
我做了一个小测试工具,它是一个 shell 脚本,但它让其他人更容易尝试我正在尝试的东西 :D
测试.sh
#!/usr/bin/env bash
set -euxo pipefail
rm -rf itertoolsmodule.c setup.py venv
PYTHON=3.5
FUNCTION=filterfalse
INIT=PyInit_
#PYTHON=2.7
#FUNCTION=ifilterfalse
#INIT=init
wget "https://raw.githubusercontent.com/python/cpython/$PYTHON/Modules/itertoolsmodule.c"
sed -i "s/${INIT}itertools/${INIT}_myitertools/" itertoolsmodule.c
sed -i 's/"itertools"/"_myitertools"/' itertoolsmodule.c
cat > setup.py << EOF
from setuptools import setup, Extension
mod = Extension('_myitertools', ['itertoolsmodule.c'])
setup(name='foo', ext_modules=[mod])
EOF
virtualenv venv -ppython"$PYTHON"
venv/bin/pip install . -v
cat > test.py << EOF
import _myitertools
import itertools
import random
import time
a = [random.random() for _ in range(500000)]
iterations = range(10)
seconds = 5
def builtins_filter():
for _ in iterations:
list(filter(None, a))
_itertools_filterfalse = itertools.$FUNCTION
def itertools_filterfalse():
for _ in iterations:
list(_itertools_filterfalse(None, a))
_myitertools_filterfalse = _myitertools.$FUNCTION
def myitertools_filterfalse():
for _ in iterations:
list(_myitertools_filterfalse(None, a))
def runbench(func):
start = time.time()
end = start + seconds
iterations = 0
while time.time() < end:
func()
iterations += 1
return iterations
for func in (builtins_filter, itertools_filterfalse, myitertools_filterfalse):
print('*' * 79)
print(func.__name__)
print('{} iterations in {} seconds'.format(runbench(func), seconds))
EOF
ubuntu16.04 x86_64 python3.5.2 (stock, apt)
(我删掉了(imo)不重要的部分):
$ ./test.sh
+ rm -rf itertoolsmodule.c setup.py venv
+ PYTHON=3.5
+ FUNCTION=filterfalse
+ INIT=PyInit_
...
+ venv/bin/pip install . -v
...
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/usr/include/python3.5m -I/tmp/foo/venv/include/python3.5m -c itertoolsmodule.c -o build/temp.linux-x86_64-3.5/itertoolsmodule.o
creating build/lib.linux-x86_64-3.5
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-Bsymbolic-functions -Wl,-z,relro -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 build/temp.linux-x86_64-3.5/itertoolsmodule.o -o build/lib.linux-x86_64-3.5/_myitertools.cpython-35m-x86_64-linux-gnu.so
...
+ venv/bin/python test.py
*******************************************************************************
builtins_filter
1401 iterations in 50 seconds
*******************************************************************************
itertools_filterfalse
1977 iterations in 50 seconds
*******************************************************************************
myitertools_filterfalse
1981 iterations in 50 seconds
ubuntu16.04 x86_64 python2.7.12(标准版,apt)
+ rm -rf itertoolsmodule.c setup.py venv
+ PYTHON=2.7
+ FUNCTION=ifilterfalse
+ INIT=init
...
+ venv/bin/pip install . -v
...
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c itertoolsmodule.c -o build/temp.linux-x86_64-2.7/itertoolsmodule.o
creating build/lib.linux-x86_64-2.7
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security -Wl,-Bsymbolic-functions -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/itertoolsmodule.o -o build/lib.linux-x86_64-2.7/_myitertools.so
...
+ venv/bin/python test.py
*******************************************************************************
builtins_filter
871 iterations in 50 seconds
*******************************************************************************
itertools_filterfalse
1918 iterations in 50 seconds
*******************************************************************************
myitertools_filterfalse
1863 iterations in 50 seconds
window !
对于 Windows,我稍微更改了脚本,因此它使用 C:\Python##\python.exe
构建了 virtualenvs(使用 mysysgit 所以我有一些 unix 工具集(bash 等) )).将内容从 bin 更改为脚本(用于 virtualenv)等。我没有/使用 conda,所以这些只是 Windows 10 上的普通 python
windows 10 python 2.7.9(股票,msi 安装程序)
+ rm -rf itertoolsmodule.c setup.py venv
+ PYTHON=2.7
+ FUNCTION=ifilterfalse
+ INIT=init
...
+ venv/Scripts/pip install . -v
...
C:\Users\Anthony\AppData\Local\Programs\Common\Microsoft\Visual C++ for Python\9.0\VC\Bin\cl.exe /c /nologo /Ox /MD /W3 /GS- /DNDEBUG -IC:\Python27\include -Ic:\users\anthony\appdata\local\temp\foo\venv\PC /Tcitertoolsmodule.c /Fobuild\temp.win32-2.7\Release\itertoolsmodule.obj
itertoolsmodule.c
creating build\lib.win32-2.7
C:\Users\Anthony\AppData\Local\Programs\Common\Microsoft\Visual C++ for Python\9.0\VC\Bin\link.exe /DLL /nologo /INCREMENTAL:NO /LIBPATH:C:\Python27\Libs /LIBPATH:c:\users\anthony\appdata\local\temp\foo\venv\libs /LIBPATH:c:\users\anthony\appdata\local\temp\foo\venv\PCbuild /EXPORT:init_myitertools build\temp.win32-2.7\Release\itertoolsmodule.obj /OUT:build\lib.win32-2.7\_myitertools.pyd /IMPLIB:build\temp.win32-2.7\Release\_myitertools.lib /MANIFESTFILE:build\temp.win32-2.7\Release\_myitertools.pyd.manifest
...
+ venv/Scripts/python test.py
*******************************************************************************
builtins_filter
914 iterations in 50 seconds
*******************************************************************************
itertools_filterfalse
2352 iterations in 50 seconds
*******************************************************************************
myitertools_filterfalse
2266 iterations in 50 seconds
windows 10 python3.5.1(股票,msi 安装程序)
+ rm -rf itertoolsmodule.c setup.py venv
+ PYTHON=3.5
+ FUNCTION=filterfalse
+ INIT=PyInit_
...
+ venv/Scripts/pip install . -v
...
D:\Programs\VS2015\VC\BIN\amd64\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MD -IC:\Python35\include -IC:\Python35\include -ID:\Programs\VS2015\VC\INCLUDE -ID:\Programs\VS2015\VC\ATLMFC\INCLUDE "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.10240.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\include\um" "-IC:\Program Files (x86)\Windows Kits\8.1\include\\shared" "-IC:\Program Files (x86)\Windows Kits\8.1\include\\um" "-IC:\Program Files (x86)\Windows Kits\8.1\include\\winrt" /Tcitertoolsmodule.c /Fobuild\temp.win-amd64-3.5\Release\itertoolsmodule.obj
itertoolsmodule.c
creating C:\Temp\pip-1fnf27jo-build\build\lib.win-amd64-3.5
D:\Programs\VS2015\VC\BIN\amd64\link.exe /nologo /INCREMENTAL:NO /LTCG /DLL /MANIFEST:EMBED,ID=2 /MANIFESTUAC:NO /LIBPATH:C:\Python35\Libs /LIBPATH:c:\users\anthony\appdata\local\temp\foo\venv\libs /LIBPATH:c:\users\anthony\appdata\local\temp\foo\venv\PCbuild\amd64 /LIBPATH:D:\Programs\VS2015\VC\LIB\amd64 /LIBPATH:D:\Programs\VS2015\VC\ATLMFC\LIB\amd64 "/LIBPATH:C:\Program Files (x86)\Windows Kits\10\lib\10.0.10240.0\ucrt\x64" "/LIBPATH:C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\lib\um\x64" "/LIBPATH:C:\Program Files (x86)\Windows Kits\8.1\lib\winv6.3\um\x64" /EXPORT:PyInit__myitertools build\temp.win-amd64-3.5\Release\itertoolsmodule.obj /OUT:build\lib.win-amd64-3.5\_myitertools.cp35-win_amd64.pyd /IMPLIB:build\temp.win-amd64-3.5\Release\_myitertools.cp35-win_amd64.lib
...
+ venv/Scripts/python test.py
*******************************************************************************
builtins_filter
658 iterations in 50 seconds
*******************************************************************************
itertools_filterfalse
2601 iterations in 50 seconds
*******************************************************************************
myitertools_filterfalse
2715 iterations in 50 seconds
结论
至少,我对 stock python 的测试表明扩展模块没有表现出不同的性能特征。
好吧,我在这上面花了半个小时,但没有制作复制品。希望这对下一个尝试这样做的可怜人有所帮助。我只能猜测 conda 正在做一些额外的优化,然后发送一个 pyconfig.h 文件,该文件位于用于编译的标志。老实说,我还没有涉足 conda 领域,所以我不知道他们的生态系统是如何运作的
关于python - 自建扩展模块比内置c模块慢,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39623764/