[C++-sig] Exposing C++ data with Boost.Python

[devin kelly]

Hello,

I'm trying to expose some data that I develop in C++ to python.  Basically,
the reverse of this sample code:

#include <iostream>
#include <python2.6/Python.h>
#include <boost/python.hpp>
#include <boost/python/exec.hpp>

int main(){

        Py_Initialize();
        object main_module = import("__main__");
        object main_namespace = main_module.attr("__dict__");
        ignored = exec("result = 5 ** 2", main_namespace);
        int five_squared = extract<int>(main_namespace["result"]);
        std::cout << five_squared << std::endl;


        return 0;
}


So this code starts the python interpreter, squares 5 (in python) and then
extracts the result to an int called five_squared.  This works fine for me,
it's basically an example straight out of the boost.python webpage.

What I'd really like to do though is have an int that I initialize in C++
and then square in python.  So this would require me to pass (or expose)
that data to python.  I've been trying this for a while and have had no luck
whatsoever.  The best I can think of is code like this:

int main(){
        Py_Initialize();
        object main_module = import("__main__");
        object main_namespace = main_module.attr("__dict__");
        main_namespace["num2square"] = 6;
        ignored = exec("result = num2square ** 2", main_namespace);
        int five_squared = extract<int>(main_namespace["result"]);
        std::cout << five_squared <<
std::endl;
        return 0;
}

This doesn't work.  Python throws an error.  What am I doing wrong??

Thanks for any help,
Devin


-- 
http://users.wpi.edu/~dkelly/
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