Converting data from C++ to Python and vice versa

SIGVerse with Python

Allowing natural assignment from C++ data type to Python data types and vice-versa is very important for seamless embedding of Python inside C++ Sigverse code To allow this kind of natural assignment, boost.python provides a system for registering converters between the languages

The aim of this tutorial is to show:

converting C++ data type to Python data type
converting Python data type to C++ data type
modifying both C++ and Python data type together

For instance, assigning an STL string to a python object looks like this:

Likewise, it is also important to be able to extract C++ objects from Python objects. Boost.python provides the extract type for this:

Please use the following code for onAction() function by using the complete code provided in the previous tutorial.

double MyController::onAction(ActionEvent &evt) {

double x=2.0;

Py_Initialize();
    try{

py::object main_module = py::import("__main__");
        // load the dictionary object out of the main module
        py::object main_namespace = main_module.attr("__dict__");
        // run simple code within the main namespace using the boost::python::exec

// Set x in python and access from C++.
        py::exec("x=42", main_namespace);
        std::cout << py::extract<int>(main_module.attr("x")) << std::endl;

// Set y from C++ and access within python.
        main_module.attr("y") = 100;
        py::exec("print y", main_namespace);

// Access and modify x in python, then access from C++.
        py::exec("x += y", main_namespace);
        std::cout << py::extract<int>(main_module.attr("x")) << std::endl;
   
   
    }
        catch(boost::python::error_already_set const &){
        // Parse and output the exception
        std::string perror_str = parse_python_exception();
        std::cout << "Error in Python: " << perror_str << std::endl;
    }

return 1.0;     
}

Please use the world file and Makefile provided in previous tutorial and use

    $make
    $sigserver.sh -w ./WorldSample.xml -p write_your_port_number

After the world file loads into sigviewer please push "Start". You shall see the following output in console

   42
   100
   142

This shows that aim of this tutorial to use boost converters from C++ to Python and vice versa have been accomplished.

If someone wants an advanced reference, please refer the following tutorial on how to write boost converters.

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