[C++-sig] Problem using wrapped void* in Python

Kor de Jong k.dejong at geog.uu.nl
Fri Nov 28 11:07:00 CET 2003

Hi all,

I am trying to wrap a C struct with Boost.Python which among other 
members has an opaque pointer to some data, for example:

// A class in C.
typedef struct AClass {
   ENUM1 v1;
   void *data;
} AClass;

// Boost.Python code to wrap AClass.
     .value("first", first)
     .value("second", second)

     .def_readwrite("v1", &A::v1)
     .def_readwrite("data", &A::data)

// Python code which uses AClass.
import amodule

var = amodule.AClass()
print var.v1
print var.data

This results in the following error message when run:
   print var.data
TypeError: No to_python (by-value) converter found for C++ type: Pv

I don't want to use the value pointed to by the void pointer in Python 
(which can't be done anyway I suppose), I just want to copy it around 
and pass it to wrapped C functions again.

So, what I am looking for is a way to tell Boost.Python how to convert 
from void* to Python and back. I have tried various things, like the 
opaque_pointer_converter and the to_python_converter, but I end up with 
code which I don't understand anymore and/or which doesn't compile. I 
would be very grateful if one of you could provide me with a bit of code 
to get me going again.

Thanks in advance!

Kor de Jong

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