如何实现Python调用C代码--python与C之间如何通信(swig)

转载: https://www.zhihu.com/question/23003213

1. C代码如何调用Python

1.1 test

#include <Python.h>    
                       
int main(int argc, char *argv[])
{
    Py_SetProgramName(argv[0]);
    Py_Initialize();   
    
    PyRun_SimpleString("print ('Hello Python!')
");

    Py_Finalize();

    return 0;

}

Linux下执行:

gcc -Wall cpython01.c -o cpython01.out -I/usr/include/python2.7 -lpython2.7

注意是Python2.7不是python3...不然好像报错....

1.2 C调用Python函数

great_module.py

#!/usr/bin/python3     
#-*- coding:utf-8 -*-  

def great_function(a):
    return a + 1     

include_module_from_py.c

#include <stdio.h>
#include <Python.h>

int include_module_from_py(int a)
{
    int res = 0;
    PyObject *pModule, *pFunc;
    PyObject *pArgs, *pValue;

    //import great_module.py 
    pModule = PyImport_Import(PyString_FromString("great_module"));  //

    //great_module.great_function(args)
    pFunc = PyObject_GetAttrString(pModule, "great_function");

    //build args
    pArgs = PyTuple_New(1);                           //Pyxxx_new录创建类型为xxx的变量
    PyTuple_SetItem(pArgs, 0, PyInt_FromLong(a));     //若a为tuple, 则a[i]=b对应于 PyTuple_SetItem(a, i, b)

    //call
    pValue = PyObject_CallObject(pFunc, pArgs);

    res = PyInt_AsLong(pValue);   

    return res;
}

int main()
{

    Py_Initialize();

    printf("res = %d
", include_module_from_py(3));

    Py_Finalize();

    return 0;
}

运行时,需要先: 

export PYTHONPATH=.:$PYTHONPATH

编译:

gcc -Wall include_module_from_py.c -o include_module.out -I/usr/include/python2.7 -lpython2.7

2. python调用C/C++

great_module.c

#include <stdio.h>
#include <Python.h>

int great_function(int a)
{
    return a + 1;
}

static PyObject * _great_function(PyObject *self, PyObject *args)
{
    int _a; 
    int res;

    //负责将Python的参数转换为C的参数
    if (!PyArg_ParseTuple(args, "i", &_a))
    {   
        return NULL;
    }   

    res = great_function(_a);

    return PyLong_FromLong(res);

}

//导出表, 负责告诉Python这个模块有哪些函数可以被Python调用
static PyMethodDef GreateModuleMethods[] = { 
    {   
        "great_function",         // 函数名
        _great_function,          // 包裹函数
        METH_VARARGS,             // 参数变长 
        ""                        // 说明性文字
    },  
    { NULL, NULL, 0, NULL }       //总是如此 
};

//导出函数, 名字: module名称+前缀init
PyMODINIT_FUNC initgreat_module()
{

    (void) Py_InitModule("great_module", GreateModuleMethods);
}

gcc -fPIC -shared great_module.c -o great_module.so -I/usr/include/python2.7 -lpython2.7

3. ctypes: Python调用C

#include <stdio.h>

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

double add_double(double a, double b)
{
    return a + b;
}

gcc -shared -Wl,-soname,adder -o adder.so -fPIC add.c

#!/usr/bin/python3
#-*- coding:utf-8 -*-

from ctypes import *


adder = CDLL('./adder.so')


res_int = adder.add_int(4, 5)
print("4 + 5 = %d " % (res_int))

a = c_double(5.5)
b = c_double(4.1)

add_double = adder.add_double
add_double.restype = c_double 
print("5.5 + 4.1 = ", str(add_double(a, b)))

工作中用了之后, 想想看还是用ctypes方便点....工程生成.so动态链接库, 然后直接在Python里导入. 

最好是在C代码中, 将需要的功能接口写的易调用点!! 然后Python也不需要传很多的参数, 直接获取一个结果等等...

4. 使用SWIG使Python调用C/C++ 

example.h

#include <iostream>
using namespace std;

class Example {
    public:
        void say_hello();
    
};

example.cpp

#include "example.h"

void Example::say_hello()
{
    cout << "hello
";
}

example.i

%module example
%{
#include "example.h"
%}
%include "example.h"

setup.py

#!/usr/bin/python3
#-*- coding:utf-8 -*-

"""
setup.py file for SWIG C++/Python example
"""
from distutils.core import setup, Extension

example_module = Extension('_example',
    sources=['example.cpp', 'example_wrap.cxx',],
)

setup (
    name = 'example',
    version = '0.1',
    author = "douzi",
    description = """Simple swig C++/Python example""",
    ext_modules = [example_module],
    py_modules = ["example"],
)

然后使用:

swig -c++ -python example.i
python3 setup.py build_ext --inplace

 https://blog.csdn.net/gxt_gy/article/details/50341215