Python接口(1):使用Python调用C/C++的种种方法

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Python是解释性语言, 底层就是用c实现的, 所以用python调用C是很容易的, 下面就总结一下各种调用的方法, 给出例子, 所有例子都在ubuntu9.10, python2.6下试过.

1. Python 调用 C (base)

想在python中调用c函数, 如这儿的fact

#include <Python.h>

int fact(int n)
{
if (n <= 1)
    return 1;
else
    return n * fact(n - 1);
}

PyObject* wrap_fact(PyObject* self, PyObject* args)
{
int n, result;

if (! PyArg_ParseTuple(args, "i:fact", &n))
    return NULL;
result = fact(n);
return Py_BuildValue("i", result);
}

static PyMethodDef exampleMethods[] =
{
{"fact", wrap_fact, METH_VARARGS, "Caculate N!"},
{NULL, NULL}
};

void initexample()
{
PyObject* m;
m = Py_InitModule("example", exampleMethods);
}

把这段代码存为wrapper.c, 编成so库,

gcc -fPIC wrapper.c -o example.so -shared -I/usr/include/python2.6 -I/usr/lib/python2.6/config

然后在有此so库的目录, 进入python, 可以如下使用

import example

example.fact(4)

2. Python 调用 C++ (base)

在python中调用C++类成员函数, 如下调用TestFact类中的fact函数,

#include <Python.h>

class TestFact{
    public:
    TestFact(){};
    ~TestFact(){};
    int fact(int n);
};

int TestFact::fact(int n)
{
if (n <= 1)
    return 1;
else
    return n * (n - 1);
}

int fact(int n)
{
    TestFact t;
    return t.fact(n);
}

PyObject* wrap_fact(PyObject* self, PyObject* args)
{
int n, result;

if (! PyArg_ParseTuple(args, "i:fact", &n))
return NULL;
result = fact(n);
return Py_BuildValue("i", result);
}

static PyMethodDef exampleMethods[] =
{
{"fact", wrap_fact, METH_VARARGS, "Caculate N!"},
{NULL, NULL}
};

extern "C" //不加会导致找不到initexample
void initexample()
{
PyObject* m;
m = Py_InitModule("example", exampleMethods);
}

把这段代码存为wrapper.cpp, 编成so库,

g++ -fPIC wrapper.cpp -o example.so -shared -I/usr/include/python2.6 -I/usr/lib/python2.6/config

然后在有此so库的目录, 进入python, 可以如下使用

import example

example.fact(4)

3. Python 调用 C++ (Boost.Python)

Boost库是非常强大的库, 其中的python库可以用来封装c++被python调用, 功能比较强大, 不但可以封装函数还能封装类, 类成员.

http://dev.gameres.com/Program/Abstract/Building%20Hybrid%20Systems%20with%20Boost_Python.CHN.by.JERRY.htm

首先在ubuntu下安装boost.python, apt-get install libboost-python-dev

#include <boost/python.hpp>
char const* greet()
{
   return "hello, world";
}

BOOST_PYTHON_MODULE(hello)
{
    using namespace boost::python;
    def("greet", greet);
}

把代码存为hello.cpp, 编译成so库

g++ hello.cpp -o hello.so -shared -I/usr/include/python2.5 -I/usr/lib/python2.5/config -lboost_python-gcc42-mt-1_34_1

此处python路径设为你的python路径, 并且必须加-lboost_python-gcc42-mt-1_34_1, 这个库名不一定是这个, 去/user/lib查

然后在有此so库的目录, 进入python, 可以如下使用

>>> import hello
>>> hello.greet()
'hello, world'

4. python 调用 c++ (ctypes)

ctypes is an advanced ffi (Foreign Function Interface) package for Python 2.3 and higher. In Python 2.5 it is already included.

ctypes allows to call functions in dlls/shared libraries and has extensive facilities to create, access and manipulate simple and complicated C data types in Python - in other words: wrap libraries in pure Python. It is even possible to implement C callback functions in pure Python.

http://python.net/crew/theller/ctypes/

#include <Python.h>

class TestFact{
    public:
    TestFact(){};
    ~TestFact(){};
    int fact(int n);
};

int TestFact::fact(int n)
{
if (n <= 1)
    return 1;
else
    return n * (n - 1);
}

extern "C"
int fact(int n)
{
    TestFact t;
    return t.fact(n);
}
将代码存为wrapper.cpp不用写python接口封装, 直接编译成so库,