[C++-sig] How to create a custom exception derived from Exception

[Glenn Ramsey]

Using boost::python how can I create an a custom exception that is derived from 
Python's Exception? The functionality I would like to get by doing this is to 
provide additional methods for the catching code to retrieve information from 
the exception.

I know it is possible to just wrap and throw my own exception class but it seems 
that because it is not derived from Exception then in certain situations I get 
the error "SystemError: 'finally' pops bad exception".

This example [1] shows how to wrap a C++ exception class...

class MyCPPException : public std::exception {...}

using namespace boost::python;
...

PyObject *myCPPExceptionType=0;

void translate(MyCPPException const &e)
{
    PyErr_SetObject(myCPPExceptionType, object(e).ptr());
}


BOOST_PYTHON_MODULE(MyModule)
{
    ...
        
    class_<MyCPPException> myCPPExceptionClass("MyCPPException"...);
    myCPPExceptionClass
        .def("get_extra_info", &MyCPPException::get_extra_info);

    myCPPExceptionType=myCPPExceptionClass.ptr();

    register_exception_translator<MyCPPException>(&translate);
    ...
}

But this is not derived from Exception.

This example [2] shows how to create an exception that is derived from 
Exception.

PyObject* createExceptionClass(const char* name, PyObject* baseTypeObj = 
PyExc_Exception)
{
    using std::string;
    namespace bp = boost::python;

    string scopeName = bp::extract<string>(bp::scope().attr("__name__"));
    string qualifiedName0 = scopeName + "." + name;
    char* qualifiedName1 = const_cast<char*>(qualifiedName0.c_str());

    PyObject* typeObj = PyErr_NewException(qualifiedName1, baseTypeObj, 0);
    if(!typeObj) bp::throw_error_already_set();
    bp::scope().attr(name) = bp::handle<>(bp::borrowed(typeObj));
    return typeObj;
}

PyObject* myExceptionTypeObj = 0;

void translate(MyCPPException const &e)
{
    PyErr_SetObject(myExceptionTypeObj, object(e).ptr());
}


BOOST_PYTHON_MODULE(MyModule)
{
    register_exception_translator<MyCPPException>(&translateFunc);
    ...
    myExceptionTypeObj = createExceptionClass("MyException");
    ...
}

But this doesn't have any custom methods to get info from the exception.

How can I do both at the same time?

Glenn

[2] 
<http://stackoverflow.com/questions/9620268/boost-python-custom-exception-class>

[1] 
<http://stackoverflow.com/questions/2261858/boostpython-export-custom-exception>
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