Get through Python and C++

Python is the best glue language in the world (PHP is the best language in the world, of course), and the simplicity of Python and the efficiency of C++ can solve 99% of the problems

In general, Python and C++ interactions fall into two categories:

1. Extending Python with C++ : when a performance bottleneck occurs in a Python project, remove the bottleneck and wrap it in C++ into a module that Python can call (the so library);
2. Embed C++ in Python: when a C++ project has features that are expected to change frequently for greater flexibility, implement those features in Python and call them in C++. This article will briefly introduce one of the practices in the first part.

Boost.Python

Boost is a treasure trove that provides the functionality we need. Also, Boost.Python is used by default in many of Boost’s libraries, so it’s been well tested.

The installation

Hello World

Implement a module in C++ that, when called in Python, returns a specific string.

#include <boost/python.hpp>

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

BOOST_PYTHON_MODULE(hello_boostpy)
{
	using namespace boost::python;
	def("greet", greet);
}
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Too simple, the code basically says it all ~

Compile it into a dynamically linked library form:

G++ -i /usr/include/python2.7/-fpic-shared -o hello_boostpy.so hello_boostpy.cc -lboost_pythonCopy the code

You can use LDD to see if hello_boostpy.so can find libboost_python. If not, add its path manually to the environment variable LD_LIBRARY_PATH, or use ldconfig.

Now you can use the hello_boostpy library in Python:

# -*- coding: utf-8 -*-
import sys
sys.path.append('.')


def test():
    import hello_boostpy
    return hello_boostpy.greet()


if __name__ == "__main__":
    print test()
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Expose Class

#include <boost/python.hpp>
#include <vector>
#include <string>
#include <sstream>
using namespace boost::python;

struct Person
{
	void set_name(std::string name) { this->name = name; }
	std::string print_info();
	void set_items(list& prices, list& discounts);
	
	
	std::string name;
	std::vector<double> item_prices;
	std::vector<double> item_discounts;
};
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void Person::set_items(list& prices, list& discounts) { for(int i = 0; i < len(prices); ++i) { double price = extract<double>(prices[i]); double discount = extract<double>(discounts[i]); item_prices.push_back(price); item_discounts.push_back(discount); }}Copy the code

BOOST_PYTHON_MODULE(person)
{
	class_<Person>("Person")
		.def("set_name", &Person::set_name)
		.def("print_info", &Person::print_info)
		.def("set_items", &Person::set_items)
	;	
}
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# -*- coding: utf-8 -*- import sys sys.path.append('.') def test(): Import person p = person.person () p.set_name('Qie') p.set_items([100, 123.456, 888.8], [0.3, 0.1, 0.5]) print p.p rint_info () if __name__ = = "__main__" : the test ()Copy the code

Py++

The module packaging process above still looks a bit boring, with a lot of repetitious work. Can it be done automatically? Py++ provides the ability to automatically generate Boost.Python code, greatly reducing the workload and error probability for modules with a large number of interfaces. For details, see Tutorial

For more on Boost.Python, see GitHub Saber in the Tutorial of the official documentation

Recommended reading:

Python coroutines: from yield/send to async/await/ exploring how to hotfix Python programs how to estimate the memory footprint of a Python object

Reprint please indicate the source: blog.guoyb.com/2017/11/05/…

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