C++ call Python code

oh ..but I can compile above successfully and run the program  
Just I need to call Python code now, do I need the SDK still?

the topic you're tackling here is quite a very difficult one, since it is not limited to just execute some python code, but to pass objects forth and back. Of course this is possible, but not without quite a lot of work, because you need some sort of conversion tool - that translates c++ objects into python objects and back again.

To ease all that trouble, SWIG http://www.swig.org/ has been developed. It's quite a nifty tool, but still  not so easy to handle especially when you want to implement something not so ordinary.

If you really need to call that python code I'd rather suggest to use Swig instead of other perhaps direct ways to interface to pyhton libs, because it's most likely to be better upgradeable. But when the complexity you there, is too much for you I'd rather suggest staying away from calling that python code and stick to rewriting it in c++.

oh really? but I have to do so since I want to incorporate Python as the scription engine.  And I will use BOOST.

So you sure I cannot get any solution here even by increasing the points?  If yes, I am better to close this post and not wait here.

Ok if I dont pass object. Is there any ways that when I modify the Python code, my C++ can get the modified values??

Sure. Why not start with

def multiply(a,b):
    print "Will compute", a, "times", b
    return a*b

And you can get result with

object result = eval("multiply(2,3)");
int c = extract<int>(result);

mish33,
 Thanks!  But if I change the value of Python Code, how does my C++ code know the changes?
In your case, you simply pass the parameters in the Python Code.

If you modify the code (either in embedded string like in the example above or in external file you call) the new code will be executed (unless that is a loaded module).

mish33

hm..if you don't mind , can you modify my code above and let me test?

sorry mish33, do you mind to make a change of my code?

Not really. I still don't understand what you are trying to achieve. Usually one doesn't change code, we only change data. Please elaborate.

I would like to allow user to change the script inside Python and the changed value will be run in C++.

So C++ calls Python code to do something and the user can write their own script inside Python and the results will be returned to C++.

Just like the game engine has scripting function.  For example, in Second Lfe, we can write our own script using LSL

int main( int argc, char ** argv ) {

  try {
    Py_Initialize();


    object main_module((
      handle<>(borrowed(PyImport_AddModule("__main__")))));

    object main_namespace = main_module.attr("__dict__");
    exec_file("multiply.py",
                                      main_namespace.ptr(),
                                      main_namespace.ptr() );

   int a = extract<int>(main_namespace.attr("a"));
   int b = extract<int>(main_namespace.attr("b"));
  printf("%d * %d = %d\n", a,b,a*b );

  } catch( error_already_set ) {
    PyErr_Print();
  }
}


multiply.py
a=5
b=12

oh so we don't need to C++ Class concept?  If I want to use C++  class/ object concept can it be done too?

You will need that to call your classes from python later on.
For that simple example it'll just obscure the basics.

thanks for your comment.  Can I accept this questions and post a new one?  and you try to help me?  I am new in Python and I would like to do a game like application that allow user to write a script.

So I hope to use C++, Create a class / objects and pass to Python to do something.  Then the object and the change stuff will return back to C++.  Pass object is the main concept that I want to see how it works  In web, I found similar things  but I don't know how to make use of it with the .py file

Hope you can help
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright David Abrahams 2002.
// 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)

// Example by Vladimir Prus that passes C++ object into Python, and
// call that object back from Python. Based on:

// embedded_hello -- A simple Boost.Python embedding example -- by
// Dirk Gerrits

#include <boost/python.hpp>
#include <boost/scoped_ptr.hpp>
#include <boost/bind.hpp>
#include <iostream>
#include <stdexcept>
#include <cassert>

using namespace boost::python;
namespace python = boost::python;

void export_classes_to_python();

class B
{
public:
    void say() const
    {
      std::cout << "B::say()\n";
    }
};

class InterfaceForPython
{
public:
    void say() const
    {
        std::cout << "InterfaceForPython::say(), address is " << this << "\n";
    }    

    void run() const
    {      
        std::cout << "InterfaceForPython::run(), address is " << this << "\n";
      std::cout << "About to call Python function\n";
        export_classes_to_python();

        Py_Initialize();

        // Retrieve the main module
        object main_module((
            handle<>(python::borrowed(PyImport_AddModule("__main__")))));

        // Retrieve the main module's namespace
        object main_namespace((main_module.attr("__dict__")));
      
      B* b = new B;

//      If called here, we get exception in executing PyRun_String
          main_namespace["context"] = ptr(b);

        // Prepare the Python code. We'll call the 'foo' method.
        python::handle<> result(
            PyRun_String(
                  "from embedded_hello import *\n"
             "def foo(p): print 'Calling C++ method from Python'; p.say(); context.say()\n"
           "",
             Py_file_input, main_namespace.ptr(), main_namespace.ptr())
            );
        // Result is not needed
        result.reset();

// Works fine here      
//          main_namespace["context"] = ptr(b);

        // Get the 'foo' function.
        object foo(main_module.attr("foo"));
   
        // Invoke it, passing ourselfs *by pointer*.
        foo(ptr(this));
    }
};


BOOST_PYTHON_MODULE(embedded_hello)
{
    class_<InterfaceForPython>("InterfaceForPython")
        .def("say", &InterfaceForPython::say);
    class_<B>("B")
      .def("say", &B::say);      
}


void export_classes_to_python()
{
    // Register the module with the interpreter
    if (PyImport_AppendInittab("embedded_hello", initembedded_hello) == -1)
        throw std::runtime_error("Failed to add embedded_hello to the interpreter's "
                                 "builtin modules");
}

int main()
{
    InterfaceForPython pyint;
   
    if (python::handle_exception(boost::bind(&InterfaceForPython::run, pyint)))
    {
        if (PyErr_Occurred())
            PyErr_Print();
        return 1;
    }

    return 0;
}