python object to native c++ pointer

Question

Im toying around with the idea to use python as an embedded scripting language for a project im working on and have got most things working. However i cant seem to be able to convert a python extended object back into a native c++ pointer.

So this is my class:

class CGEGameModeBase
{
public:
    virtual void FunctionCall()=0;
    virtual const char* StringReturn()=0;
};

class CGEPYGameMode : public CGEGameModeBase, public boost::python::wrapper<CGEPYGameMode>
{
public:
    virtual void FunctionCall()
    {
        if (override f = this->get_override("FunctionCall"))
            f();
    }

    virtual const char* StringReturn()
    {
        if (override f = this->get_override("StringReturn"))
            return f();

        return "FAILED TO CALL";
    }
};

Boost wrapping:

BOOST_PYTHON_MODULE(GEGameMode)
{
    class_<CGEGameModeBase, boost::noncopyable>("CGEGameModeBase", no_init);

    class_<CGEPYGameMode, bases<CGEGameModeBase> >("CGEPYGameMode", no_init)
        .def("FunctionCall", &CGEPYGameMode::FunctionCall)
        .def("StringReturn", &CGEPYGameMode::StringReturn);
}

and the python code:

import GEGameMode

def Ident():
    return "Alpha"

def NewGamePlay():
    return "NewAlpha"


def NewAlpha():
    import GEGameMode
    import GEUtil

    class Alpha(GEGameMode.CGEPYGameMode):
        def __init__(self):
            print "Made new Alpha!"

        def FunctionCall(self):
            GEUtil.Msg("This is function test Alpha!")

        def StringReturn(self):
            return "This is return test Alpha!"

    return Alpha()

Now i can call the first to functions fine by doing this:

const char* ident = extract< const char* >( GetLocalDict()["Ident"]() );
const char* newgameplay = extract< const char* >( GetLocalDict()["NewGamePlay"]() );

printf("Loading Script: %s\n", ident);
CGEPYGameMode* m_pGameMode = extract< CGEPYGameMode* >( GetLocalDict()[newgameplay]() );

However when i try and convert the Alpha class back to its base class (last line above) i get an boost error:

TypeError: No registered converter was able to extract a C++ pointer to type class CGEPYGameMode from this Python object of type Alpha

I have done alot of searching on the net but cant work out how to convert the Alpha object into its base class pointer. I could leave it as an object but rather have it as a pointer so some non python aware code can use it. Any ideas?

Answer 1

Thanks to Stefan from the python c++ mailling list, i was missing

super(Alpha, self).__init__()

from the constructor call meaning it never made the parent class. Thought this would of been automatic :D

Only other issue i had was saving the new class instance as a global var otherwise it got cleaned up as it went out of scope.

So happy now