[C++-sig] runtime error R6025 - pure virtual function call

[Dave Wolfe]

I'm being driven slowly mad by the following error:

  C:\projects\PyScheduler\dtest.exe
  In PyHelloPrinter.__init__()...

  runtime error R6025
  - pure virtual function call

The setup is: I've written the simplest C++ app I could manage that
embeds Python, and tries to create (in C++) an instance of a Python
class (defined in pyhello.py) that implements a C++-defined interface.

I've spent an embarrassing number of hours trying to figure this out. If
I don't find a solution soon, I'll be forced to conclude that I am
simply too dense to use Boost.Python. `:-}
  
I'm using ActiveState Python 2.4.3 on (32-bit) WinXP, and a snapshot of
boost downloaded from CVS a few days ago.  Compiler is VC++ 7.1.
Everything works fine from Python; if I say: "python pyhello.py" it runs
with no problems.  But I get 'runtime error R6025' without fail when I
try to run my C++ app.

The code I'm running, shorn of all adornments, is appended below.  Any
help is *much* appreciated!

TIA,

- Dave W.

----------

// File: main.cpp
ICallable* CreatePythonHelloPrinter(std::string greetee)
{
    ICallable* retval = NULL;
    try
    {
        bpl::object main = bpl::import("__main__");
        bpl::object global = main.attr("__dict__");
        bpl::exec_file("pyhello.py", global, global);
        bpl::object PyHelloPrinter = global["PyHelloPrinter"];
        bpl::object myPyPrinter = PyHelloPrinter(greetee);
        retval = bpl::extract<ICallable*>(myPyPrinter);
    }
    catch (bpl::error_already_set const&)
    {
        std::cerr << GetPythonException();
    }
    
    return retval;
}

int main()
{
    // Init the python interpreter
    Py_Initialize();
    
    ICallable*  pyGreeter = CreatePythonHelloPrinter("World");
    if (pyGreeter) pyGreeter->operator()();

    // Shut down python
    Py_Finalize();
}


----------
# File: pyhello.py
from Callable import *

class PyHelloPrinter(ICallable):
    def __init__(self, greetee):
        ICallable.__init__(self)
        self._name = greetee
    def __call__(self):
        print 'PyHelloPrinter(): Hello, %s!' % (self._name,)

----------
// File: Callable.h
#ifndef CALLABLE_H
#define CALLABLE_H

#include <boost/noncopyable.hpp>

struct ICallable
{
    virtual ~ICallable() { }
    virtual void operator()() = 0;
};

#endif // !CALLABLE_H

----------
// File: Callable.cpp

#include <Callable.h>
#include <boost/python.hpp>

using namespace boost::python;

struct PyWrap_ICallable : ICallable, wrapper<ICallable>
{
    void operator()()
    {
        if (override func = get_override("__call__"))
            func();
    }
};

BOOST_PYTHON_MODULE(Callable)
{
    class_<PyWrap_ICallable, boost::noncopyable>("ICallable")
        .def("__call__", pure_virtual(&ICallable::operator() ) )
        ;
}