use boost.python to Warp C++ for python

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在python中调用c++

c++ 速度快，python 比较方便，如果同时用到python和c++中库，则需要相互调用。目前python发展迅速，很多新库都以python为主，但一些传统或者强调速度的库依然是用c++写的。因此掌握这一技能，可以加速开发，避免重复地制造车轮。

介绍

在python中调用c++的方法很多，出名的有swig, boost.python，个人属于刚入门，由于对boost库有好感，觉得代表着c++方面最先进的技术。boost.python的理念也很好，不用去学习接口语言，不用修改源代码，直接快速上手。

官方文档

• quick start
• 接口语法
• bjam documence

写一个小测试

• cpp.cpp: c++源文件
• py.py: python 测试文件
• Jamroot: boost.python 配置文件

安装boost环境

sudo apt-get install libboost-all-dev

再下载一个boost 源代码，这样可以进行下面的官方测试并得到配置文件Jamroot

官方测试

• hello world
• cd /home/yzbx/Downloads/boost_1_61_0/libs/python/example/tutorial
• bjam

warning: mismatched versions of Boost.Build engine and core
warning: Boost.Build engine (bjam) is 2014.03.00
warning: Boost.Build core (at /media/yzbx/NewPartition/home/yzbx/Downloads/boost_1_61_0/tools/build/src) is 2015.07-git
notice: no Python configured in user-config.jam
notice: will use default configuration
warning: No toolsets are configured.
warning: Configuring default toolset "gcc".
warning: If the default is wrong, your build may not work correctly.
warning: Use the "toolset=xxxxx" option to override our guess.
warning: For more configuration options, please consult
warning: http://boost.org/boost-build2/doc/html/bbv2/advanced/configuration.html
Performing configuration checks

    - 32-bit                   : no  (cached)
    - 64-bit                   : yes (cached)
    - arm                      : no  (cached)
    - mips1                    : no  (cached)
    - power                    : no  (cached)
    - sparc                    : no  (cached)
    - x86                      : yes (cached)
    - symlinks supported       : yes (cached)
...patience...
...patience...
...found 1833 targets...

• python hello.py

hello, world

• 官方测试目录，输出一大堆如bin,xxx.so

$: tree /home/yzbx/Downloads/boost_1_61_0/libs/python/example/tutorial
/home/yzbx/Downloads/boost_1_61_0/libs/python/example/tutorial
├── bin
│   ├── config.log
│   ├── gcc-5.4.0
│   │   └── debug
│   │       ├── hello_ext.so
│   │       └── hello.o
│   ├── hello.test
│   │   └── gcc-5.4.0
│   │       └── debug
│   │           ├── hello
│   │           ├── hello.output
│   │           └── hello.test
│   └── project-cache.jam
├── hello.cpp
├── hello_ext.so
├── hello.py
├── Jamroot
├── libboost_python.so -> libboost_python.so.1.61.0
├── libboost_python.so.1 -> libboost_python.so.1.61.0
├── libboost_python.so.1.61 -> libboost_python.so.1.61.0
└── libboost_python.so.1.61.0

• 上面的命令运行成功，说明安装boost.python环境成功！

在ubuntu16.04上基于官方测试进行更改

1. struct or class ? 写c++一般用class，不过用class就要加public，否则默认为private就无法在python中调用。
2. bjam 如何使用配置？

Simply copy the file and tweak use-project boost to where your boost root directory is and you're OK.

The comments contained in the Jamrules file above should be sufficient to get you going. 

上面说只要指定boost的根目录，再按Jamroot中的注释去更改就okay!

3. 如上图，在个人测试文件夹下有三个文件：cpp.cpp,py.py,Jamroot，将root根目录设置为/home/yzbx/Downloads/boost_1_61_0, 再将python 模块名改为yzbx_ext，再将源文件和测试文件改为cpp.cpp,py.py, 并将测试输出目录改为yzbx
4. 个人测试文件的输出，通过对比，不难了解各个参数的含义

$: tree ~/test/boost-python/
/home/yzbx/test/boost-python/
├── bin
│   ├── config.log
│   ├── gcc-5.4.0
│   │   └── debug
│   │       ├── cpp.o
│   │       └── yzbx_ext.so
│   ├── project-cache.jam
│   └── yzbx.test
│       └── gcc-5.4.0
│           └── debug
│               ├── yzbx
│               ├── yzbx.output
│               └── yzbx.test
├── cpp.cpp
├── Jamroot
├── libboost_python.so -> libboost_python.so.1.61.0
├── libboost_python.so.1 -> libboost_python.so.1.61.0
├── libboost_python.so.1.61 -> libboost_python.so.1.61.0
├── libboost_python.so.1.61.0
├── py.py
└── yzbx_ext.so

附件

cpp.cpp

//  Copyright Joel de Guzman 2002-2004. Distributed under the Boost
//  Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt
//  or copy at http://www.boost.org/LICENSE_1_0.txt)
//  Hello World Example from the tutorial
//  [Joel de Guzman 10/9/2002]

#include <boost/python.hpp>
#include <boost/python/module.hpp>
#include <boost/python/def.hpp>


char const* greet()
{
   return "hello, world";
}

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

struct bgs{
void set(int a){this->a=a;}
int getA(){return a;}
    int a;
};

class Var
{
public:
    Var(std::string name) : name(name), value() {}
    std::string const name;
    float value;
};

BOOST_PYTHON_MODULE(yzbx_ext)
{
    using namespace boost::python;
    def("greet", greet);
    def("add",add);
    class_<bgs>("bgs")
        .def("set",&bgs::set)
        .def("getA",&bgs::getA)
        .def_readonly("a",&bgs::a)
    ;

    class_<Var>("Var", init<std::string>())
    .def_readonly("name", &Var::name)
    .def_readwrite("value", &Var::value);
}

py.py

#  Copyright Joel de Guzman 2002-2007. Distributed under the Boost
#  Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt
#  or copy at http://www.boost.org/LICENSE_1_0.txt)
#  Hello World Example from the tutorial

import yzbx_ext
print yzbx_ext.greet()
print yzbx_ext.add(3,5)
bgs=yzbx_ext.bgs()
bgs.set(10)
print bgs.getA()
var=yzbx_ext.Var("pi")
var.value=3.14
print var.name,' is around ', var.value

Jamroot

# Copyright David Abrahams 2006. Distributed under the Boost
# Software License, Version 1.0. (See accompanying
# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

import python ;

if ! [ python.configured ]
{
    ECHO "notice: no Python configured in user-config.jam" ;
    ECHO "notice: will use default configuration" ;
    using python ;
}

# Specify the path to the Boost project.  If you move this project,
# adjust this path to refer to the Boost root directory.
use-project boost
  : /home/yzbx/Downloads/boost_1_61_0 ;

# Set up the project-wide requirements that everything uses the
# boost_python library from the project whose global ID is
# /boost/python.
project
  : requirements <library>/boost/python//boost_python 
                 <implicit-dependency>/boost//headers 
  : usage-requirements <implicit-dependency>/boost//headers 
  ;

# Declare the three extension modules.  You can specify multiple
# source files after the colon separated by spaces.
python-extension yzbx_ext : cpp.cpp ;

# Put the extension and Boost.Python DLL in the current directory, so
# that running script by hand works.
install convenient_copy 
  : yzbx_ext 
  : <install-dependencies>on <install-type>SHARED_LIB <install-type>PYTHON_EXTENSION 
    <location>. 
  ;

# A little "rule" (function) to clean up the syntax of declaring tests
# of these extension modules.
local rule run-test ( test-name : sources + )
{
    import testing ;
    testing.make-test run-pyd : $(sources) : : $(test-name) ;
}

# Declare test targets
run-test yzbx : yzbx_ext py.py ;