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

[Marcelo M. <mm...@ac...>]

I think you are trying to re-implement by hand the "director" feature.

Read the Python docs about director, the main idea is like this:

You enable directors using the 'directors' option and the %director feature:

-------- myodule.i -------
%module(directors=1) mymodule

%director SolverReporter;

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


Then, in python you use:

class PythonSolverReporter(mymodule.SoverReporter):
    def __init__(self, something):
        self.somtheing = something
        mymodule.SoverReporter.__init__(self)

    def report(self, status):           //overload SoverReporter::report
         if self.something:
            print status.something
         ...
    

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


and that is, 'reporter' is a C++ SoverReporter object for Simulation,
but execute the python code you define in the python side, ie:

     def report(self, status):           //overload SoverReporter::report
         if self.something:
            print status.something
         ...


Marcelo


John Pye wrote:

> 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
>
>
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