Python接口(1):使用Python调用C/C++的种种方法

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,
g++ -fPIC wrapper.cpp -o example.so -shared -I/usr/include/python2.6 -I/usr/lib/python2.6/config
 
进入python, 可以如下使用
>>> import ctypes

>>> pdll = ctypes.CDLL('/home/ubuntu/tmp/example.so')

>>> pdll.fact(4)

12