Python的C/C++扩展——boost_python编写Python模块

前面讲述了Python使用ctypes直接调用动态库和使用Python的C语言API封装C函数，本文概述方便封装C++类给Python使用的boost_python库。

安装boost python库：

sudo aptitude install libboost-python-dev

示例

下面代码简单实现了一个普通函数maxab()和一个Student类：

#include <iostream>
#include <string>

int maxab(int a, int b) { return a>b?a:b; }

class Student {
    private:
        int age;
        std::string name;

    public:
        Student() {}
        Student(std::string const& _name, int _age) { name=_name; age=_age; }

        static void myrole() { std::cout << "I'm a student!" << std::endl; }

        void whoami() { std::cout << "I am " << name << std::endl; }

        bool operator==(Student const& s) const { return age == s.age; }
        bool operator!=(Student const& s) const { return age != s.age; }

};

使用boost.python库封装也很简单，如下代码所示：

#include <Python.h>
#include <boost/python.hpp>
#include <boost/python/suite/indexing/vector_indexing_suite.hpp>
#include <vector>

#include "student.h"

using namespace boost::python;

BOOST_PYTHON_MODULE(student) {                                                                                                                                                                              
    // This will enable user-defined docstrings and python signatures,
    // while disabling the C++ signatures
    scope().attr("__version__") = "1.0.0";
    scope().attr("__doc__") = "a demo module to use boost_python.";
    docstring_options local_docstring_options(true, false, false);
    def(
            "maxab", &maxab, "return max of two numbers.\n"
       );  

    class_<Student>("Student", "a class of student")
        .def(init<>())
        .def(init<std::string, int>())
        // methods for Chinese word segmentation
        .def(
                "whoami", &Student::whoami, "method's doc string..."
            )   
        .def(
                "myrole", &Student::myrole, "method's doc string..."
            )   
        .staticmethod("myrole");
    // 封装STL
    class_<std::vector<Student> >("StudentVec")
        .def(vector_indexing_suite<std::vector<Student> >())
        ;   
}

上述代码还是include了Python.h文件，如果不include的话，会报错误：

wrap_python.hpp:50:23: fatal error: pyconfig.h: No such file or directory

编译

编译以上代码有两种方式，一种是在命令行下面直接使用g++编译：

g++ -I/usr/include/python2.7  -fPIC wrap_student.cpp -lboost_python -shared -o student.so

首先指定Python.h的路径，如果是Python 3的话就要修改为相应的路径，编译wrap_student.cpp要指定-fPIC参数，链接(-lboost_python)生成动态库(-shared)。 生成的student.so动态库就可以被python直接import使用了

In [1]: import student

In [2]: student.maxab(2, 5)
Out[2]: 5

In [3]: s = student.Student('Tom', 12)

In [4]: s.whoami()
I am Tom

In [5]: s.myrole()
I'm a student!
另外一直方法是用python的setuptools编写setup.py脚本：

#!/usr/bin/env python

from setuptools import setup, Extension

setup(name="student",
    ext_modules=[
    Extension("student", ["wrap_student.cpp"],                                                                                                                                                              
    libraries = ["boost_python"])
])

然后执行命令编译：

python setup.py build
or
sudo python setup.py install

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