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Sat Apr 28 18:55:01 EDT 2001 · http://mail.python.org/pipermail/python-list/2001-April/080641.html

"Tom" <NoSpam at NoSpam.com> wrote in message
news:T8HG6.20396$HF.4234648 at news4.rdc1.on.home.com...
>
> In args[0] you have a PyObject*.
> If the PyObject is actually one of your PyAtoms, you can cast it as such.
> (PyAtom inherits - I'm assuming - from cxx::PythonExtension<> which
inherits
> from PyObject.)
> Unfortunately, we can't do a safe 'dynamic_cast' because the inheritance
of
> PyObject is non-virtual, so we'll do it the C way:
>     assert( thePyObject->ob_type == PyAtom::type_object() );    // or
throw.
>     PyAtom* pPyAtom = static_cast< PyAtom* >( thePyObject );
>
> I think this is right, but no guarantees.  Tell me if I'm wrong.
>

It was close enough to lead me to something that works:
Py::Object PyBond::GetNbrAtom(const Py::Tuple& args){
  PyObject *pyObj=args[0].ptr();
  if( pyObj->ob_type != PyAtom::type_object() ){
    throw Py::ValueError("argument must be a PyAtom");
  }
  PyAtom *a = static_cast<PyAtom *>(pyObj);

Thanks for the pointer!
-greg

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CXX extension types question