Python与C语言混合编程：通过distutils或setuptools实现的一个简单的C扩展
这个介绍一个扩展Python组件的例子，组件是通过C语言开发的(用python的Ｃ-API实现)， 然后通过python的distutils组件安装，例子中内容来自《python cocobook》英文版，一本非常不错的书。
目录结构
首先目录结构如下
dev
|__sample.h
|__sample.c
|__subtest01
|__pysample.c
|__setup.py
|__libsample.so
源码内容
sample.h
/* sample.h */
extern int gcd(int x, int y);
extern int in_mandel(double x0, double y0, int n);
extern int divide(int a, int b, int *remainder);
extern double avg(double *a, int n);
typedef struct Point {
double x,y;
} Point;
extern double distance(Point *p1, Point *p2);sample.c
/* sample.c */
#include
/* Compute the greatest common divisor */
int gcd(int x, int y) {
int g = y;
while (x > 0) {
g = x;
x = y % x;
y = g;
}
return g;
}
/* Test if (x0,y0) is in the Mandelbrot set or not */
int in_mandel(double x0, double y0, int n) {
double x=0,y=0,xtemp;
while (n > 0) {
xtemp = x*x - y*y + x0;
y = 2*x*y + y0;
x = xtemp;
n -= 1;
if (x*x + y*y > 4) return 0;
}
return 1;
}
/* Divide two numbers */
int divide(int a, int b, int *remainder) {
int quot = a / b;
*remainder = a % b;
return quot;
}
/* Average values in an array */
double avg(double *a, int n) {
int i;
double total = 0.0;
for (i = 0; i < n; i++) {
total += a[i];
}
return total / n;
}
/* A C data structure */
typedef struct Point {
double x,y;
} Point;
/* Function involving a C data structure */
double distance(Point *p1, Point *p2) {
return hypot(p1->x - p2->x, p1->y - p2->y);
} pysample.c
#include "Python.h"
#include "sample.h"
/* int gcd(int, int) */
static PyObject *py_gcd(PyObject *self, PyObject *args) {
int x, y, result;
if (!PyArg_ParseTuple(args,"ii", &x, &y)) {
return NULL;
}
result = gcd(x,y);
return Py_BuildValue("i", result);
}
/* int in_mandel(double, double, int) */
static PyObject *py_in_mandel(PyObject *self, PyObject *args) {
double x0, y0;
int n;
int result;
if (!PyArg_ParseTuple(args, "ddi", &x0, &y0, &n)) {
return NULL;
}
result = in_mandel(x0,y0,n);
return Py_BuildValue("i", result);
}
/* int divide(int, int, int *) */
static PyObject *py_divide(PyObject *self, PyObject *args) {
int a, b, quotient, remainder;
if (!PyArg_ParseTuple(args, "ii", &a, &b)) {
return NULL;
}
quotient = divide(a,b, &remainder);
return Py_BuildValue("(ii)", quotient, remainder);
}
/* Module method table */
static PyMethodDef SampleMethods[] = {
{"gcd", py_gcd, METH_VARARGS, "Greatest common divisor"},
{"in_mandel", py_in_mandel, METH_VARARGS, "Mandelbrot test"},
{"divide", py_divide, METH_VARARGS, "Integer division"},
{ NULL, NULL, 0, NULL}
};
/* Module structure */
static struct PyModuleDef samplemodule = {
PyModuleDef_HEAD_INIT,
"sample", /* name of module */
"A sample module", /* Doc string (may be NULL) */
-1, /* Size of per-interpreter state or -1 */
SampleMethods /* Method table */
};
/* Module initialization function */
PyMODINIT_FUNC
PyInit_sample(void) {
return PyModule_Create(&samplemodule);
}setup.py
# setup.py
from distutils.core import setup, Extension
setup(name="sample",
ext_modules=[
Extension("sample",
["../sample.c", "pysample.c"],
include_dirs = ['..'],
)
]
)编译安装
在目录subtest01下面，直接编译安装
（注意一般情况下，大家直接使用python命令即可，我使用的是自己编译的版本python372，编译过程可参考：
https://blog.csdn.net/tanmx219/article/details/86518446）
$ python372 setup.py build_ext --inplace
此时会输出一些信息，
running build_ext
building 'sample' extension
creating build
creating build/temp.linux-x86_64-3.7-pydebug
gcc -pthread -Wno-unused-result -Wsign-compare -g -Og -Wall -fPIC -fPIC -I.. -I/usr/local/include/python3.7dm -c ../sample.c -o build/temp.linux-x86_64-3.7-pydebug/../sample.o
gcc -pthread -Wno-unused-result -Wsign-compare -g -Og -Wall -fPIC -fPIC -I.. -I/usr/local/include/python3.7dm -c pysample.c -o build/temp.linux-x86_64-3.7-pydebug/pysample.o
gcc -pthread -shared build/temp.linux-x86_64-3.7-pydebug/../sample.o build/temp.linux-x86_64-3.7-pydebug/pysample.o -L/usr/local/lib -lpython3.7dm -o /home/matthew/dev/tutorial/subtest01/sample.cpython-37dm-x86_64-linux-gnu.so此时，如果你要在subtest01目录下启动python372，是可以直接使用sample这个组件的，如，
$ python372
Python 3.7.2 (default, Jan 18 2019, 20:12:21)
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sample
>>> sample.gcd(35,42)
7
>>> sample.divide(42,8)
(5, 2)
>>> sample
>>> exit()
但若要在任意目录下都能运行sample组件，则需要把组件拷贝到python的库目录下面，
$ sudo cp sample.cpython-37dm-x86_64-linux-gnu.so /usr/local/lib/python3.7/lib-dynload/测试完了就删除掉吧，没啥用
$ sudo rm -f /usr/local/lib/python3.7/lib-dynload/sample.cpython-37dm-x86_64-linux-gnu.so整个过程还是比较简单的。
如果你的工程项目比较大的话，相信都会综合应用一些相关的工具来实现，比如cmake，那么这些安装卸载的东西就能通过cmake脚本实现啦。
使用setuptools
本质上setuptools和distutils没有什么太大的不同，可以看作是distutils的增强版。所以如果你想使用setuptools，只要在setup.py中把distutils换成setuptools即可，下面我给出本演示中可以使用的完整的setup.py源码，编译安装命令仍然是上面那个：
｀python setup.py build_ext --inplace｀
# setup.py
from setuptools import setup, Extension
setup(name="sample",
ext_modules=[
Extension("sample",
["../sample.c", "pysample.c"],
include_dirs = ['..'],
)
]
)如果你想把打包发布的话，使用命令｀python setup.py sdist｀会得到一个压缩包，拷贝到你需要的地方解压缩再｀python setup.py install｀就可以了，这个过程这里就不再展开详述了。
其他工具
其他工具如cython, swig我都没怎么用过，这里给个链接为参考：
https://blog.csdn.net/tanmx219/article/details/86666456
还有一个工具pybind11（python + c++11)，这个在pytorch源码third-party中有用到，源码量也比较少，参考：
https://github.com/pybind/pybind11
参考资料
https://packaging.python.org/
https://media.readthedocs.org/pdf/python-packaging-user-guide/latest/python-packaging-user-guide.pdf
https://thomasnyberg.com/cpp_extension_modules.html
https://thomasnyberg.com/what_are_extension_modules.html
