[C++-sig] keeping weak_ptrs upon python objects smart_ptr holders

[Nicolas LELONG]

Hi everyone,

I've been trying to wrap my Observer pattern implementation with BPL. I'm
willing to be able to create new observers in Python.
My listeners objects keep weak_ptrs upon their observers, these weak_ptrs
are used to notify the observers and to be able to know if a given observer
is still "alive".

I have not been able to obtain a weak_ptr that references the real
shared_ptr holding the observer objects. The weak_ptrs I get seem to
reference a dummy smart_ptr which is destoyed after the execution of
python::detail::caller_arity<>::impl<>::operator().

The 'problem' can be seen with the following code :

**** c++ code **********************************************

struct A
{
    virtual ~A(){}
    virtual std::string f() = 0;
};

struct ACallback :  A,  Callback
{
    ACallback (PyObject* self) : Callback(self) {}

    std::string f()
    {
      object self(handle<>(borrowed(mSelf)));
      return extract<std::string>(self.attr("f")());
    }
};

boost::weak_ptr<A> instance;

void setInstance(boost::shared_ptr<A> a) { instance = a; };

std::string doInstance()
{
  boost::shared_ptr<A> a = instance.lock();
  if (a.get() == NULL)
    return "no more object here!";
  else
    return a->f();
};

BOOST_PYTHON_MODULE( test )
{
  class_<A, ACallback, boost::noncopyable>("A")
    .def("f", pure_virtual(&A::f));

  def("setInstance", setInstance);
  def("doInstance", doInstance);
}

******** python script ***************************

from test import *

class E(A):
  def f(self):
    return 'E::f'

e = E()
setInstance(e)
res0 = doInstance()
res1 = e.f()

***************************************************

At the end of the script, res0 contains 'no more object here!' and res1
contains what I'd like res0 to contain : 'E::f' !

I did not find any information that could help me to solve this problem.
Is there any known way to achieve this or am I doomed to get rid of
weak_ptrs ?!

Thanks,
Nicolas.