[Swig-user] Passing a wrapped C++ object to a python callback

[John P. <joh...@st...>]

Hi all,

I'm having trouble using Py_BuildValue to pass a SWIG-wrapped *C++ 
object* back to my python callback function. It says in the python docs 
that I can pass a PyObject using the "o" string, but I'm not sure how I 
can cast my C++ object to a PyObject from inside C++. What's the correct 
way of doing that?

Here are some details: I'm setting up a callback mechanism for a Python 
method to display selected status data from a C++ solver engine. In C++ 
I have written a class 'SolverReporter':

class SolverReporter{
    SolverReporter();
    virtual ~SolverReporter();
    virtual int report(const SolverStatus &status) = 0;
}

Then I have written a subclass PythonSolverReporter with the constructor

PythonSolverReporter::PythonSolverReporter(PyObject *pyfunc){
    this->pyfunc = pyfunc;
    Py_INCREF(pyfunc);
}

and now, there's the 'report' method, and *this* is what I'm struggling 
with:

int PythonSolverReporter::report(const SolverStatus &status){
    PyObject *pyarglist, *pyresult;
    pyarglist = Py_BuildValue("(o)",status); // <------------------ what 
to do here?
    pyresult = PyEval_CallObject(this->pyfunc,pyarglist);
    Py_DECREF(pyarglist);
}

Usage of all this in Python would be like this, for example:

def show_something(status):
    print "Solver status is",status.getIterationNum()

reporter = PythonSolverReporter(show_something)
simulation = Simulation(...)
simulation.solve(reporter)

Any suggestions -- even if it's a completely different way of doing 
things -- would be really appreciated.

Cheers
JP