利用Boost.Python实现Python C/C++混合编程

学习中如果碰到问题，参考官网例子：

D:\boost_1_61_0\libs\python\test

参考：Boost.Python 中英文文档。

利用Boost.Python实现Python C/C++混合编程

导出函数

#include<string>#include<boost/python.hpp>using namespace std;using namespace boost::python;char const * greet(){    return "hello,world";}BOOST_PYTHON_MODULE(hello_ext){    def("greet", greet);}

python:

import hello_extprint hello_ext.greet()

导出类：

导出默认构造的函数的类

c++

#include<string>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct World{    void set(string msg) { this->msg = msg; }    string greet() { return msg; }    string msg;};BOOST_PYTHON_MODULE(hello) //导出的module 名字{    class_<World>("World")        .def("greet", &World::greet)        .def("set", &World::set);}

python:

import hello planet = hello.World() # 调用默认构造函数，产生类对象planet.set("howdy")   # 调用对象的方法print planet.greet() # 调用对象的方法

构造函数的导出：

#include<string>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct World{    World(string msg):msg(msg){} //增加构造函数    World(double a, double b):a(a),b(b) {} //另外一个构造函数    void set(string msg) { this->msg = msg; }    string greet() { return msg; }    double sum_s() { return a + b; }    string msg;    double a;    double b;};BOOST_PYTHON_MODULE(hello) //导出的module 名字{    class_<World>("World",init<string>())         .def(init<double,double>()) // expose another construct        .def("greet", &World::greet)        .def("set", &World::set)        .def("sum_s", &World::sum_s);}

python 测试调用：

import helloplanet = hello.World(5,6)planet2 = hello.World("hollo world")print planet.sum_s()print planet2.greet()

如果不想导出任何构造函数，则使用no_init:

class_<Abstract>("Abstract",no_init)

类的数据成员

#include<string>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct Var{    Var(string name):name(name),value(){}    string const name;    float value;};BOOST_PYTHON_MODULE(hello_var){    class_<Var>("Var", init<string>())        .def_readonly("name", &Var::name) //只读        .def_readwrite("value", &Var::value); //读写}

python调用:

import hello_varvar = hello_var.Var("hello_var")var.value = 3.14# var.name = 'hello' # errorprint var.name

C++类对象导出为Python的类对象，注意var.name不能赋值。

类的属性

// 类的属性#include<string>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct Num{    Num(){}    float get() const { return val; }    void set(float val) { this->val = val; }    float val;};BOOST_PYTHON_MODULE(hello_num){    class_<Num>("Num")        .add_property("rovalue", &Num::get) // 对外：只读        .add_property("value", &Num::get, &Num::set);// 对外读写 .value值会改变.rovalue值，存储着同样的数据。}

python:

import hello_numnum = hello_num.Num()num.value = 10print num.rovalue #  result: 10

继承

// 类的继承#include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct Base {    virtual ~Base() {};    virtual string getName() { return "Base"; }    string str;};struct Derived : Base {    string getName() { return "Derived"; }};void b(Base *base) { cout << base->getName() << endl; };void d(Derived *derived) { cout << derived->getName() << endl; };Base * factory() { return new Derived; }/*    下面的额外的代码如果去掉会报错。    解决地址：http://stackoverflow.com/questions/38261530/unresolved-external-symbols-since-visual-studio-2015-update-3-boost-python-link/38291152#38291152*/namespace boost{    template <>    Base const volatile * get_pointer<class Base const volatile >(        class Base const volatile *c)    {        return c;    }}BOOST_PYTHON_MODULE(hello_derived){    class_<Base>("Base")        .def("getName", &Base::getName)        .def_readwrite("str", &Base::str);    class_<Derived, bases<Base> >("Derived")        .def("getName", &Derived::getName)        .def_readwrite("str", &Derived::str);    def("b", b);    def("d", d);    def("factory", factory,        return_value_policy<manage_new_object>());//}

python:

import hello_derivedderive = hello_derived.factory()hello_derived.d(derive)

类的虚函数：

/* 类的虚函数，实现的功能是：可以编写Python类，来继承C++类*/#include<boost/python.hpp>#include<boost/python/wrapper.hpp>#include<string>#include<iostream>using namespace boost::python;using namespace std;struct Base{    virtual ~Base() {}    virtual int f() { return 0; };};struct BaseWrap : Base, wrapper<Base>{    int f()    {        if (override f = this->get_override("f"))            return f(); //如果函数进行重载了，则返回重载的        return Base::f(); //否则返回基类    }    int default_f() { return this->Base::f(); }};BOOST_PYTHON_MODULE(hello_virtual){    class_<BaseWrap, boost::noncopyable>("Base")        .def("f", &Base::f, &BaseWrap::default_f);}

python：

import hello_virtual base = hello_virtual.Base()# 定义派生类，继承C++类class Derived(hello_virtual.Base):    def f(self):        return 42derived = Derived()print base.f()print derived.f()

类的运算符/特殊函数

// 类的运算符/特殊函数#include<string>#include<iostream>// #include<boost/python.hpp> 如果仅包含该头文件，会出错#include <boost/python/operators.hpp>#include <boost/python/class.hpp>#include <boost/python/module.hpp>#include <boost/python/def.hpp>#include <boost/operators.hpp>using namespace std;using namespace boost::python;class FilePos{public:    FilePos() :len(0) {}    operator double()const { return len; };//重载类型转换符    int len;};// operator 方法FilePos operator+(FilePos pos, int a){    pos.len = pos.len + a;    return pos; //返回的是副本}FilePos operator+(int a, FilePos pos){    pos.len = pos.len + a;    return pos; //返回的是副本}int operator-(FilePos pos1, FilePos pos2){    return (pos1.len - pos2.len);}FilePos operator-(FilePos pos, int a){    pos.len = pos.len - a;    return pos;}FilePos &operator+=(FilePos & pos, int a){    pos.len = pos.len + a;    return pos;}FilePos &operator-=(FilePos & pos, int a){    pos.len = pos.len - a;    return pos;}bool operator<(FilePos  pos1, FilePos pos2){    if (pos1.len < pos2.len)        return true;    return false;}//特殊的方法FilePos pow(FilePos pos1, FilePos pos2){    FilePos res;    res.len = std::pow(pos1.len, pos2.len);    return res;}FilePos abs(FilePos pos){    FilePos res;    res.len = std::abs(pos.len);    return res;}ostream& operator<<(ostream& out, FilePos pos){    out << pos.len;    return out;}BOOST_PYTHON_MODULE(hello_operator){    class_<FilePos>("FilePos")        .def_readwrite("len",&FilePos::len)        .def(self + int())        .def(int() + self)        .def(self - self)        .def(self - int())        .def(self += int())        .def(self -= other<int>())        .def(self < self)        .def(float_(self))//特殊方法 ,     __float__        .def(pow(self, other<FilePos>()))  // __pow__        .def(abs(self))         //  __abs__        .def(str(self));                //  __str__ for ostream}

注意上面的：.def(pow(self, other<FilePos>()))模板后面要加上括号。也要注意头文件的包含，否则会引发错误。

python:

import hello_operatorfilepos1 = hello_operator.FilePos()filepos1.len = 10filepos2 = hello_operator.FilePos()filepos2.len = 20;print filepos1 - filepos2

函数

函数的调用策略。

// 函数的调用策略 #include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct X{    string str;};struct Z{    int value;};struct Y{    X x;    Z *z;    int z_value() { return z->value; }};X & f(Y &y, Z*z){    y.z = z;    return y.x;  //因为x是y的数据成员，x的声明周期与y进行了绑定。因为我们的目的是：Python接口应尽可能的反映C++接口}BOOST_PYTHON_MODULE(hello_call_policy){    class_<Y>("Y")        .def_readwrite("x", &Y::x)        .def_readwrite("z", &Y::z)        .def("z_value", &Y::z_value);    class_<X>("X")        .def_readwrite("str", &X::str);    class_<Z>("Z")        .def_readwrite("value", &Z::value);    // return_internal_reference<1 表示返回的值与第一个参数有关系：即第一个参数是返回对象的拥有者（y和x都是引用的形式)。    // with_custodian_and_ward<1, 2> 表示第二个参数的生命周期依赖于第一个参数的生命周期。    def("f", f, return_internal_reference<1, with_custodian_and_ward<1, 2> >());}

函数重载

// overloading#include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct X{    bool f(int a)    {        return true;    }    bool f(int a, double b)    {        return true;    }    bool f(int a, double b, char c)    {        return true;    }    int f(int a, int b, int c)    {        return a + b + c;    }};bool (X::*fx1)(int) = &X::f;bool(X::*fx2)(int, double) = &X::f;bool(X::*fx3)(int, double,char) = &X::f;int(X::*fx4)(int, int,int) = &X::f;BOOST_PYTHON_MODULE(hello_overloaded){    class_<X>("X")        .def("f", fx1)        .def("f", fx2)        .def("f", fx3)        .def("f", fx4);}

python:

import hello_overloadedx = hello_overloaded.X() # create a new objectprint x.f(1)  # default int typeprint x.f(2,double(3))print x.f(4,double(5),chr(6))  # chr(6) convert * to char print x.f(7,8,9)

默认参数

普通函数的默认参数：

然而通过上面的方式对重载函数进行封装时，就丢失了默认参数的信息。当然我们可以通过一般形式的封装，如下：

int f(int,double = 3.14,char const * = "hello");int f1(int x){ return f(x);}int f2(int x,double y){return f(x,y)}//int module initdef("f",f); // 所有参数def("f",f2); //两个参数def("f",f1); //一个参数

但是通过上面的形式封装很麻烦。我们可以通过宏的形式，为我们批量完成上面的功能。

C++:

// BOOST_PYTHON_FUNCTION_OVERLOADS#include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;void foo(int a, char b = 1, unsigned c = 2, double d = 3){    return;}BOOST_PYTHON_FUNCTION_OVERLOADS(foo_overloads, foo, 1, 4); // 参数个数的最小为1，最大为4BOOST_PYTHON_MODULE(hello_overloaded){    def("foo", foo, foo_overloads()); //实现导出带有默认参数的函数}

python:

import hello_overloadedhello_overloaded.foo(1)hello_overloaded.foo(1,chr(2))hello_overloaded.foo(1,chr(2),3)  # 3对应的C++为unsigned inthello_overloaded.foo(1,chr(2),3,double(4))

成员函数的默认参数：

//使用BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS 宏，完成成员函数默认参数的接口#include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct george{    void wack_em(int a, int b = 0, char c = 'x')    {        return;    }};BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(george_overloads, wack_em, 1, 3); // 参数个数的最小为1，最大为3BOOST_PYTHON_MODULE(hello_member_overloaded){    class_<george>("george")        .def("wack_em", &george::wack_em, george_overloads());}

python:

import hello_member_overloadedc = hello_member_overloaded.george()c.wack_em(1)c.wack_em(1,2)c.wack_em(1,2,chr(3))

利用init和optional实现构造函数的重载。
使用方法如下：

// init  optional#include<string>#include<iostream>#include<boost/python.hpp>using namespace std;using namespace boost::python;struct X{    X(int a, char b = 'D', string c = "constructor", double b = 0.0) {}};BOOST_PYTHON_MODULE(hello_construct_overloaded){    class_<X>("X")        .def(init<int, optional<char, string, double> >()); // init 和 optional}

对象接口

Python 是动态类型的语言，C++是静态类型的。Python变量可能是：integer,float ,list ,dict,tuple,str,long,等等，还有其他类型。从Boost.Python和C++的观点来看，Python中的变量是类object的实例，在本节，我们看一下如何处理Python对象。

基本接口

// init  optional#include<string>#include<iostream>#include<boost/python.hpp>#include <numpy/arrayobject.h>using namespace std;using namespace boost::python;namespace bp = boost::python;void f(object x){    int y = extract<int>(x); // retrieve an int from x}int g(object x){    extract<int> get_int(x);    if (get_int.check())        return get_int();    else        return 0;}int test(object &x){    dict d = extract<dict>(x.attr("__dict__"));    d["whatever"] = 4;    return 0;}int test2(dict & d){    d["helloworld"] = 3;    return 0;}class A {public:    list lst;    void listOperation(list &lst) {};};// 传入np.array数组对象，让C++进行处理int add_arr_1(object & data_obj, object rows_obj, object cols_obj){    PyArrayObject* data_arr = reinterpret_cast<PyArrayObject*>(data_obj.ptr());    float * data = static_cast<float *>(PyArray_DATA(data_arr));    // using data    int rows = extract<int>(rows_obj);    int cols = extract<int>(cols_obj);    for (int i = 0; i < rows*cols; i++)    {        data[i] += 1;    }    return 0;}BOOST_PYTHON_MODULE(hello_object){    def("test", test);    def("test2", test2);    def("add_arr_1", add_arr_1);}

python 调用：

import hello_objectdic1 = {"whatever":1}hello_object.test2(dic1)arr = np.array([1,2,3],dtype = float32)print arr.dtypeprint arrhello_object.add_arr_1(arr,1,3)print arr