[C++-sig] Re: Converting a C++ object to python

[David Abrahams]

Raoul Gough <RaoulGough at yahoo.co.uk> writes:

G> "Ron Penton" <rpenton at adelphia.net> writes:
>
>>>If you catch a boost::python::error_already_set in C++, I guess you
>>>can get more information by calling PyErr_Print(), which should dump a
>>>standard Python traceback on stderr. At a guess, you're getting a
>>>Python TypeError from the object constructor, because it doesn't have
>>>a converter for booga *. BTW, why are you passing a pointer to b,
>>>instead of a reference?
>>
>> PyErr_Print says "TypeError: No Python class registered for C++ class class
>> booga",
>> which confirms what you thought.
>
> Well, not really - I would have thought that there is a problem with
> booga * (i.e. pointer to booga), but from your error message, that is
> not the case. I don't suppose it makes any difference to use b instead
> of &b then?
>
>>
>> The part that confuses me is the converter part; I'm not quite sure how to
>> go about creating one. All of the examples I can find go about the creation
>> of the python types manually, rather than using the class_ definition, so
>> I'm really unsure of where to go from here.
>
> Well, we've now snipped the original code, but looking back at it from
> your original post:
>
>> class booga{public:    
>> booga() : a( 0 ) {}    int a;    void 
>> looga() { a = a + 10; cout << a << endl; }};
>> BOOST_PYTHON_MODULE( wrap ){    class_<booga>( "booga" 
>> )        .def( "looga", &amp;booga::looga 
>> );}
>> int main(){    Py_Initialize();    
>>  
>>     PyImport_AppendInittab( 
>> "wrap", initwrap );
>>     booga b;    
>> object obj( &amp;b );
>
> the class_<booga> constructor should handle all of the converter
> registration. However, I know that at least *some* of the registration
> is done at run-time. 

All of it, except for some built-in to-python conversions like those
for int, char const*, etc.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com