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191 lines
5.0 KiB
Markdown
191 lines
5.0 KiB
Markdown
# Cython：Typed memoryviews
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## 例子
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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：
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In [1]:
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```py
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%%file cython_sum.pyx
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def cython_sum(double[::1] a):
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cdef double s = 0.0
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cdef int i, n = a.shape[0]
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for i in range(n):
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s += a[i]
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return s
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```
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```py
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Writing cython_sum.pyx
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```
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In [2]:
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```py
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%%file setup.py
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from distutils.core import setup
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from distutils.extension import Extension
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from Cython.Distutils import build_ext
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ext = Extension("cython_sum", ["cython_sum.pyx"])
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setup(
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cmdclass = {'build_ext': build_ext},
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ext_modules = [ext],
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)
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```
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```py
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Writing setup.py
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```
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In [3]:
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```py
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!python setup.py build_ext -i
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```
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```py
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running build_ext
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cythoning cython_sum.pyx to cython_sum.c
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building 'cython_sum' extension
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creating build
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creating build\temp.win-amd64-2.7
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creating build\temp.win-amd64-2.7\Release
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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
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writing build\temp.win-amd64-2.7\Release\cython_sum.def
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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"
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```
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```py
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cython_sum.c: In function '__Pyx_BufFmt_ProcessTypeChunk':
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cython_sum.c:13561:26: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13561:26: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13561:26: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c:13613:20: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13613:20: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13613:20: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__pyx_buffmt_parse_array':
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cython_sum.c:13675:25: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13675:25: warning: format '%d' expects argument of type 'int', but argument 3 has type 'size_t' [-Wformat]
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cython_sum.c:13675:25: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__Pyx_GetBufferAndValidate':
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cython_sum.c:13860:7: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13860:7: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
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cython_sum.c:13860:7: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:13860:7: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__Pyx_RaiseArgtupleInvalid':
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cython_sum.c:14032:18: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:14032:18: warning: format '%s' expects argument of type 'char *', but argument 5 has type 'Py_ssize_t' [-Wformat]
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cython_sum.c:14032:18: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:14032:18: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__Pyx_RaiseTooManyValuesError':
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cython_sum.c:14552:18: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:14552:18: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__Pyx_RaiseNeedMoreValuesError':
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cython_sum.c:14558:18: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:14558:18: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
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cython_sum.c:14558:18: warning: too many arguments for format [-Wformat-extra-args]
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cython_sum.c: In function '__Pyx_ValidateAndInit_memviewslice':
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cython_sum.c:15253:22: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:15253:22: warning: format '%s' expects argument of type 'char *', but argument 3 has type 'Py_ssize_t' [-Wformat]
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cython_sum.c:15253:22: warning: unknown conversion type character 'z' in format [-Wformat]
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cython_sum.c:15253:22: warning: too many arguments for format [-Wformat-extra-args]
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```
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In [4]:
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```py
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from cython_sum import cython_sum
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from numpy import *
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```
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In [5]:
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```py
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a = arange(1e6)
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```
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检查正确性：
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In [6]:
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```py
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cython_sum(a)
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```
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Out[6]:
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```py
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499999500000.0
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```
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In [7]:
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```py
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a.sum()
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```
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Out[7]:
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```py
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499999500000.0
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```
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效率：
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In [8]:
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```py
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%timeit cython_sum(a)
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```
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```py
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100 loops, best of 3: 2.14 ms per loop
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```
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In [9]:
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```py
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%timeit a.sum()
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```
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```py
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100 loops, best of 3: 2.38 ms per loop
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```
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In [10]:
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```py
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import zipfile
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f = zipfile.ZipFile('07-06-cython-sum.zip','w',zipfile.ZIP_DEFLATED)
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names = ['cython_sum.pyx',
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'setup.py']
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for name in names:
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f.write(name)
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f.close()
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!rm -f setup*.*
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!rm -f cython_sum*.*
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!rm -rf build
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``` |