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335 lines
5.9 KiB
Markdown
335 lines
5.9 KiB
Markdown
# Cython：Cython 语法，调用其他C库
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## Cython 语法
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### cdef 关键词
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`cdef` 定义 `C` 类型变量。
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可以定义局部变量：
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```py
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def fib(int n):
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cdef int a,b,i
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...
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```
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定义函数返回值：
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```py
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cdef float distance(float *x, float *y, int n):
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cdef:
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int i
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float d = 0.0
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for i in range(n):
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d += (x[i] - y[i]) ** 2
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return d
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```
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定义函数：
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```py
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cdef class Particle(object):
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cdef float psn[3], vel[3]
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cdef int id
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```
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注意函数的参数不需要使用 cdef 的定义。
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### def, cdef, cpdef 函数
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`Cython` 一共有三种定义方式，`def, cdef, cpdef` 三种：
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* `def` - Python, Cython 都可以调用
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* `cdef` - 更快，只能 Cython 调用，可以使用指针
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* `cpdef` - Python, Cython 都可以调用，不能使用指针
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### cimport
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In [1]:
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```py
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from math import sin as pysin
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from numpy import sin as npsin
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```
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In [2]:
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```py
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%load_ext Cython
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```
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从标准 `C` 语言库中调用模块，`cimport` 只能在 `Cython` 中使用：
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In [3]:
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```py
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%%cython
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from libc.math cimport sin
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from libc.stdlib cimport malloc, free
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```
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### cimport 和 pxd 文件
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如果想在多个文件中复用 `Cython` 代码，可以定义一个 `.pxd` 文件（相当于头文件 `.h`）定义方法，这个文件对应于一个 `.pyx` 文件（相当于源文件 `.c`），然后在其他的文件中使用 `cimport` 导入：
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`fib.pxd, fib.pyx` 文件存在，那么可以这样调用：
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```py
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from fib cimport fib
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```
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还可以调用 `C++` 标准库和 `Numpy C Api` 中的文件：
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```py
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from libcpp.vector cimport vector
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cimport numpy as cnp
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```
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## 调用其他C库
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从标准库 `string.h` 中调用 `strlen`：
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In [4]:
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```py
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%%file len_extern.pyx
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cdef extern from "string.h":
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int strlen(char *c)
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def get_len(char *message):
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return strlen(message)
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```
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```py
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Writing len_extern.pyx
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```
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不过 `Cython` 不会自动扫描导入的头文件，所以要使用的函数必须再声明一遍：
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In [5]:
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```py
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%%file setup_len_extern.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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setup(
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ext_modules=[ Extension("len_extern", ["len_extern.pyx"]) ],
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cmdclass = {'build_ext': build_ext}
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)
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```
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```py
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Writing setup_len_extern.py
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```
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编译：
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In [6]:
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```py
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!python setup_len_extern.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 len_extern.pyx to len_extern.c
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building 'len_extern' 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 len_extern.c -o build\temp.win-amd64-2.7\Release\len_extern.o
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writing build\temp.win-amd64-2.7\Release\len_extern.def
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C:\Miniconda\Scripts\gcc.bat -DMS_WIN64 -shared -s build\temp.win-amd64-2.7\Release\len_extern.o build\temp.win-amd64-2.7\Release\len_extern.def -LC:\Miniconda\libs -LC:\Miniconda\PCbuild\amd64 -lpython27 -lmsvcr90 -o "C:\Users\Jin\Documents\Git\python-tutorial\07\. interfacing with other languages\len_extern.pyd"
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```
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从 `Python` 中调用：
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In [7]:
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```py
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import len_extern
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```
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调用这个模块后，并不能直接使用 `strlen` 函数，可以看到，这个模块中并没有 `strlen` 这个函数：
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In [8]:
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```py
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dir(len_extern)
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```
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Out[8]:
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```py
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['__builtins__',
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'__doc__',
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'__file__',
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'__name__',
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'__package__',
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'__test__',
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'get_len']
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```
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不过可以调用 `get_len` 函数：
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In [9]:
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```py
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len_extern.get_len('hello')
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```
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Out[9]:
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```py
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5
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```
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因为调用的是 `C` 函数，所以函数的表现与 `C` 语言的用法一致，例如 `C` 语言以 `\0` 为字符串的结束符，所以会出现这样的情况：
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In [10]:
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```py
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len_extern.get_len('hello\0world!')
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```
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Out[10]:
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```py
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5
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```
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除了对已有的 `C` 函数进行调用，还可以对已有的 `C` 结构体进行调用和修改：
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In [11]:
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```py
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%%file time_extern.pyx
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cdef extern from "time.h":
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struct tm:
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int tm_mday
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int tm_mon
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int tm_year
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ctypedef long time_t
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tm* localtime(time_t *timer)
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time_t time(time_t *tloc)
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def get_date():
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"""Return a tuple with the current day, month and year."""
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cdef time_t t
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cdef tm* ts
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t = time(NULL)
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ts = localtime(&t)
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return ts.tm_mday, ts.tm_mon + 1, ts.tm_year + 1900
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```
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```py
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Writing time_extern.pyx
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```
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这里我们只使用 `tm` 结构体的年月日信息，所以只声明了要用了三个属性。
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In [12]:
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```py
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%%file setup_time_extern.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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setup(
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ext_modules=[ Extension("time_extern", ["time_extern.pyx"]) ],
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cmdclass = {'build_ext': build_ext}
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)
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```
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```py
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Writing setup_time_extern.py
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```
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编译：
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In [13]:
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```py
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!python setup_time_extern.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 time_extern.pyx to time_extern.c
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building 'time_extern' extension
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C:\Miniconda\Scripts\gcc.bat -DMS_WIN64 -mdll -O -Wall -IC:\Miniconda\include -IC:\Miniconda\PC -c time_extern.c -o build\temp.win-amd64-2.7\Release\time_extern.o
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writing build\temp.win-amd64-2.7\Release\time_extern.def
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C:\Miniconda\Scripts\gcc.bat -DMS_WIN64 -shared -s build\temp.win-amd64-2.7\Release\time_extern.o build\temp.win-amd64-2.7\Release\time_extern.def -LC:\Miniconda\libs -LC:\Miniconda\PCbuild\amd64 -lpython27 -lmsvcr90 -o "C:\Users\Jin\Documents\Git\python-tutorial\07\. interfacing with other languages\time_extern.pyd"
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```
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测试：
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In [14]:
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```py
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import time_extern
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time_extern.get_date()
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```
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Out[14]:
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```py
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(19, 9, 2015)
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```
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清理文件：
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In [15]:
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```py
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import zipfile
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f = zipfile.ZipFile('07-04-extern.zip','w',zipfile.ZIP_DEFLATED)
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names = ['setup_len_extern.py',
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'len_extern.pyx',
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'setup_time_extern.py',
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'time_extern.pyx']
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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 len_extern.*
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!rm -f time_extern.*
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!rm -rf build
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``` |