[C++-sig] boost python exposing const*

[MM]

I have a c++ class T that I succesfully expose via:

class_<T, T*> ...


later on, I have

struct S {
const T* underlying;
};

class_<S,S*>("S").
.def_readonly("underlying", &S::underlying)
;

From python, when I call:

s.underlying

where s is a python instance of S, i get the following error:

TypeError: No to_python (by-value) converter found for C++ type: T const*

Do I need another converter for T const* in particular? or for both T* and
T const*?
Does the class_<T,T*> above only expose T itself, not pointers to it?

Thanks
MM

[Holger Joukl]

Hi,

Post by MM
class_<T, T*> ...
later on, I have
struct S {
  const T* underlying;
};
class_<S,S*>("S").
    .def_readonly("underlying", &S::underlying)
;
s.underlying
TypeError: No to_python (by-value) converter found for C++ type: T const*
Do I need another converter for T const* in particular? or for both
T* and T const*?
Does the class_<T,T*> above only expose T itself, not pointers to it?

Using add_property() instead should be your friend, to be able to use a
call policy.

E.g.:

#include <boost/python.hpp>

namespace bp = boost::python;


// classes to expose
struct A
{
};


struct B
{
B() : underlying(NULL) { }
A const * underlying;
};


// expose to python
BOOST_PYTHON_MODULE(properties)
{

bp::class_<A>("A")
;

bp::class_<B>("B")
// Won't work: "No to_python (by-value) converter found...
//.def_readonly("underlying", &B::underlying)
.add_property("underlying", bp::make_getter(&B::underlying,
bp::return_internal_reference<>()))
;
}


See FAQ entry also:
http://www.boost.org/doc/libs/1_59_0/libs/python/doc/v2/faq.html#topythonconversionfailed

Holger

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