Cython：Typed memoryviews

例子

这里 double[::1] 是一种 memoryview 方法，效率跟 Numpy 数组差不多，可以给 C 数组赋值，可以给 Numpy 数组赋值，可以像 Numpy 一样切片：

In [1]:
%%file cython_sum.pyx
def cython_sum(double[::1] a):
    cdef double s = 0.0
    cdef int i, n = a.shape[0]
    for i in range(n):
        s += a[i]
    return s

Writing cython_sum.pyx
In [2]:
%%file setup.py
from distutils.core import setup
from distutils.extension import Extension
from Cython.Distutils import build_ext

ext = Extension("cython_sum", ["cython_sum.pyx"])

setup(
    cmdclass = {'build_ext': build_ext},
    ext_modules = [ext],
)

Writing setup.py
In [3]:
!python setup.py build_ext -i

running build_ext
cythoning cython_sum.pyx to cython_sum.c
building 'cython_sum' extension
creating build
creating build\temp.win-amd64-2.7
creating build\temp.win-amd64-2.7\Release
C:\Anaconda\Scripts\gcc.bat -DMS_WIN64 -mdll -O -Wall -IC:\Anaconda\include -IC:\Anaconda\PC -c cython_sum.c -o build\temp.win-amd64-2.7\Release\cython_sum.o
writing build\temp.win-amd64-2.7\Release\cython_sum.def
C:\Anaconda\Scripts\gcc.bat -DMS_WIN64 -shared -s build\temp.win-amd64-2.7\Release\cython_sum.o build\temp.win-amd64-2.7\Release\cython_sum.def -LC:\Anaconda\libs -LC:\Anaconda\PCbuild\amd64 -lpython27 -lmsvcr90 -o "C:\Users\lijin\Documents\Git\python-tutorial\07. interfacing with other languages\cython_sum.pyd"

cython_sum.c: In function '__Pyx_BufFmt_ProcessTypeChunk':
cython_sum.c:13561:26: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13561:26: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13561:26: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c:13613:20: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13613:20: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13613:20: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__pyx_buffmt_parse_array':
cython_sum.c:13675:25: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13675:25: warning: format '%d' expects argument of type 'int', but argument 3 has type 'size_t' [-Wformat]
cython_sum.c:13675:25: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__Pyx_GetBufferAndValidate':
cython_sum.c:13860:7: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13860:7: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
cython_sum.c:13860:7: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:13860:7: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__Pyx_RaiseArgtupleInvalid':
cython_sum.c:14032:18: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:14032:18: warning: format '%s' expects argument of type 'char *', but argument 5 has type 'Py_ssize_t' [-Wformat]
cython_sum.c:14032:18: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:14032:18: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__Pyx_RaiseTooManyValuesError':
cython_sum.c:14552:18: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:14552:18: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__Pyx_RaiseNeedMoreValuesError':
cython_sum.c:14558:18: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:14558:18: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
cython_sum.c:14558:18: warning: too many arguments for format [-Wformat-extra-args]
cython_sum.c: In function '__Pyx_ValidateAndInit_memviewslice':
cython_sum.c:15253:22: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:15253:22: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
cython_sum.c:15253:22: warning: unknown conversion type character 'z' in format [-Wformat]
cython_sum.c:15253:22: warning: too many arguments for format [-Wformat-extra-args]
In [4]:
from cython_sum import cython_sum
from numpy import *
In [5]:
a = arange(1e6)

检查正确性：

In [6]:
cython_sum(a)
Out[6]:
499999500000.0
In [7]:
a.sum()
Out[7]:
499999500000.0

效率：

In [8]:
%timeit cython_sum(a)

100 loops, best of 3: 2.14 ms per loop
In [9]:
%timeit a.sum()

100 loops, best of 3: 2.38 ms per loop
In [10]:
import zipfile

f = zipfile.ZipFile('07-06-cython-sum.zip','w',zipfile.ZIP_DEFLATED)

names = ['cython_sum.pyx',
         'setup.py']
for name in names:
    f.write(name)

f.close()

!rm -f setup*.*
!rm -f cython_sum*.*
!rm -rf build