Python调用C

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. 引言

众所周知，Python语言简单、易学、开源、具有丰富的库，Python的第一个编译器是用C语言实现的。但Python的缺点也非常明显，最让人诟病的就是Python的性能问题。因此，为了提高程序的运行效率，通常会将程序的关键部分使用C或C++重写，编译成动态链接库，然后在Python（CPython）中进行调用。运行环境：Ubuntu 16.04、Python 2.7、Python 3.5。

2. Python C扩展

2.1 普通C函数

void hello()
{
    printf("Hello World!\n");
}

int add(int a, int b)
{
    return a + b;
}

2.2 Python C扩展

Python扩展模块由以下几部分组成：

• 头文件<Python.h>
• 调用的C函数
• 模块方法表
• 模块初始化函数

具体实现demo.c如下：

// 包含Python头文件
#include <Python.h>


// 兼容Python3
#if PY_MAJOR_VERSION >= 3
#define PYTHON3
#endif


// hello函数实现
static PyObject* hello(PyObject *self, PyObject *args)
{
    printf("Hello World\n");
    return Py_None;
}


// add函数实现
static PyObject* add(PyObject *self, PyObject *args)
{
    int a, b;
    if(!PyArg_ParseTuple(args, "ii", &a, &b))
    {
        return NULL;
    }
    return Py_BuildValue("i", a + b);
}


// 模块方法表
static PyMethodDef TwoMethods[] = {
    { "hello", hello, METH_NOARGS, "Print Hello" },
    { "add", add, METH_VARARGS, "Add two integers"},
    { NULL, NULL, 0, NULL }
};


#ifdef PYTHON3
// Python3模块定义结构体
static struct PyModuleDef testModule = {
    PyModuleDef_HEAD_INIT,
    "testModule",
    "Test Module",
    -1,
    TwoMethods
};


// Python3模块初始化函数
PyMODINIT_FUNC PyInit_demo(void)
{
    return PyModule_Create(&testModule);
}


#else
// Python2模块初始化函数
PyMODINIT_FUNC initdemo(void)
{
    Py_InitModule("demo", TwoMethods);
}
#endif

2.3 编译并测试

编写setup.py文件：

from distutils.core import setup, Extension

demo = Extension('demo', sources = ['demo.c'])

setup(name = 'C extension module', version = '1.0', description = 'This is a demo', ext_modules = [demo])

生成动态链接库的命令如下：

#python2
$ python setup.py build_ext --inplace
running build_ext
building 'demo' extension
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c demo.c -o build/temp.linux-x86_64-2.7/demo.o
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security -Wl,-Bsymbolic-functions -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-x86_64-2.7/demo.o -o /workspace/python-c/demo.so

#python3
$ python3 setup.py build_ext --inplace
running build_ext
building 'demo' extension
x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/usr/include/python3.5m -c demo.c -o build/temp.linux-x86_64-3.5/demo.o
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-Bsymbolic-functions -Wl,-z,relro -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 build/temp.linux-x86_64-3.5/demo.o -o /workspace/python-c/demo.cpython-35m-x86_64-linux-gnu.so

hello，add函数测试：

>>> from demo import hello, add
>>> hello()
Hello World
>>> add(2, 3)
5

参考资料

1. https://www.cnblogs.com/vamei/archive/2013/02/06/2892628.html
2. https://www.yanxurui.cc/posts/python/2017-06-18-3-ways-of-calling-c-functions-from-python/
3. https://swe.mirsking.com/languages/python/pythoncallcplusplus
4. https://www.jianshu.com/p/cd28e8b0cce1
5. https://docs.python.org/2.7/extending/extending.html
6. https://docs.python.org/2.7/extending/building.html
7. https://tutorialedge.net/python/python-c-extensions-tutorial/