[C++-sig] Smart Pointers in Boost.Python with Automatic Dereferencing

[Ralf W. Grosse-Kunstleve]

Boost.Python has special support for boost::shared_ptr<>. E.g. this
should do what you want (untested):

  class_<A, shared_ptr<A> >("A")

It is more difficult only if you have your own smart pointers.

Ralf

----- Original Message ----
From: "Bilokon, Paul" <paul.bilokon at lehman.com>
To: Development of Python/C++ integration <c++-sig at python.org>
Sent: Monday, May 19, 2008 5:30:59 AM
Subject: [C++-sig] Smart Pointers in Boost.Python with Automatic Dereferencing


Hi all,

I'm trying to find an authoritative resource on exposing functions that
return smart pointers using Boost.Python.

So far my best example is this:

http://wiki.python.org/moin/boost.python/PointersAndSmartPointers

However, I find the need to explicitly dereference the pointer in Python
deeply unsatisfactory:

print (+an_A).hello()

This is essentially C++ programming in Python. The whole purpose of the
exercise is to avoid the need for explicit memory management!

Is there another method that will simply allow me to call

print an_A.hello()

Many thanks for your help!

Best wishes,
Paul


P.S. Just for your information I'll paste the C++ code:

#include <boost/shared_ptr.h> 
using namespace boost;

struct A {
    shared_ptr<A> create () { return shared_ptr<A>(new A); }
    std::string   hello  () { return "Just nod if you can hear me!"; }
};

BOOST_PYTHON_MODULE(shared_ptr)
{
    class_<A>("A",init<>())
        .def("create",&A::create,return_value_policy<return_by_value>())
        .staticmethod("create")
        .def("hello",&A::hello)
        ;

    class_< shared_ptr<A> >("A_ptr", init<const shared_ptr<A>& >())

.def("__pos__",&boost::shared_ptr<A>::get,return_internal_reference<>())
        ;
}

And the sample Python program:

from shared_ptr import *
an_A = A_ptr.create()
print (+an_A).hello()
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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