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244 lines
3.5 KiB
Markdown
244 lines
3.5 KiB
Markdown
# Cython：Cython 基础，将源代码转换成扩展模块
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## Cython 基础
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之前使用了手动的方法对 `C` 程序进行编译，而 `Cython` 则简化了这个过程。
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考虑之前的斐波拉契数列，`Python` 版本：
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```py
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def fib(n):
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a,b = 1,1
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for i in range(n):
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a,b = a+b, a
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return a
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```
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`C` 版本：
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```py
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int fib(int n) {
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int tmp, i, a, b;
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a = b = 1;
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for (i=0; i<n; i++) {
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tmp = a; a += b; b = tmp;
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}
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return a;
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}
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```
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`Cython` 版本：
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```py
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def fib(int n):
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cdef int i, a, b
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a,b = 1,1
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for i in range(n):
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a,b = a+b, a
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return a
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```
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这里 `cdef` 定义了 `C` 变量的类型。
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**Cython** 的好处在于，我们使用了 **Python** 的语法，又有 **C/C++** 的效率，同时省去了之前直接编译成扩展模块的麻烦，并且提供了原生的 **Numpy** 支持。
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官方网址：[http://www.cython.org](http://www.cython.org)
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其主要用法有两点：
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* 将 Python 程序转化为 C 程序
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* 包装 C/C++ 程序
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## 将源代码转换成扩展模块
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### ipython 中使用 Cython 命令
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导入 `Cython` `magic` 命令：
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In [1]:
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```py
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%load_ext Cython
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```
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使用 `magic` 命令执行 `Cython`：
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In [2]:
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```py
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%%cython
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def cyfib(int n):
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cdef int i, a, b
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a,b = 1,1
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for i in range(n):
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a,b = a+b, a
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return a
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```
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In [3]:
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```py
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cyfib(10)
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```
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Out[3]:
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```py
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144
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```
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### 使用 distutils 编译 Cython
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`Cython` 代码以 `.pyx` 结尾，先通过 cython 转化为 `.c` 文件，再用 `gcc` 转化为 `.so(.pyd)` 文件。
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In [4]:
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```py
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%%file fib.pyx
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def cyfib(int n):
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cdef int i, a, b
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a,b = 1,1
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for i in range(n):
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a,b = a+b, a
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return a
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```
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```py
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Writing fib.pyx
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```
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In [5]:
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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("fib", sources=["fib.pyx"])
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setup(ext_modules=[ext], cmdclass={'build_ext': build_ext})
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```
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```py
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Overwriting setup.py
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```
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编译成功：
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In [6]:
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```py
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!python setup.py build_ext --inplace
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```
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```py
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running build_ext
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cythoning fib.pyx to fib.c
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building 'fib' 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:\Miniconda\Scripts\gcc.bat -DMS_WIN64 -mdll -O -Wall -IC:\Miniconda\include -IC:\Miniconda\PC -c fib.c -o build\temp.win-amd64-2.7\Release\fib.o
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writing build\temp.win-amd64-2.7\Release\fib.def
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C:\Miniconda\Scripts\gcc.bat -DMS_WIN64 -shared -s build\temp.win-amd64-2.7\Release\fib.o build\temp.win-amd64-2.7\Release\fib.def -LC:\Miniconda\libs -LC:\Miniconda\PCbuild\amd64 -lpython27 -lmsvcr90 -o "C:\Users\Jin\Documents\Git\python-tutorial\07\. interfacing with other languages\fib.pyd"
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```
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使用模块：
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In [7]:
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```py
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import fib
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fib.cyfib(10)
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```
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Out[7]:
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```py
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144
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```
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In [8]:
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```py
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import zipfile
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f = zipfile.ZipFile('07-03-fib.zip','w',zipfile.ZIP_DEFLATED)
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names = 'fib.pyd fib.pyx fib.c setup.py'.split()
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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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```
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## 使用 pyximport
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清理之前生成的文件：
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In [9]:
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```py
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!rm -f fib.pyd
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!rm -f fib.pyc
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!rm -f fib.C
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```
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清理之前导入的模块：
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In [10]:
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```py
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%reset -f
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```
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使用 `pyximport`：
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In [11]:
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```py
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import pyximport
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pyximport.install()
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import fib
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fib.cyfib(10)
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```
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Out[11]:
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```py
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144
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```
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`install` 函数会自动检测 Cython 程序的变化，并自动导入，不过一般用于简单文件的编译。
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清理生成的文件：
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In [12]:
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```py
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!rm -f setup*.*
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!rm -f fib.*
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!rm -rf build
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``` |