[Boost-users] Boost Python: add_property and shared_ptr

Subject: [Boost-users] Boost Python: add_property and shared_ptr
From: Raul Durand (raul.durand_at_[hidden])
Date: 2012-07-28 23:52:52

Hi!

I've been using the boost::python library for some time with few problems
but now I got stuck.
Fortunately I isolated the problem.

In the class Domain below I defined a property called solver which returns
a  shared_ptr<Solver>  instance:

*namespace bp=boost::python;**
**class Solver
**{
**public:
**    bool _b;
**    void func() { _b = true; }
**};**
**typedef shared_ptr<Solver> Solver_ptr;**
**
class Domain
**{
**public:
**    Solver_ptr solver;
**    void set_solver(Solver_ptr s) { solver = s; }
**};**
**typedef shared_ptr<Domain> Domain_ptr;**
**
BOOST_PYTHON_MODULE(test) {**
*

* bp::class_<Solver, Solver_ptr>("Solver")*

*   .def("func", &Solver::func)*

* ;*

* bp::class_<Domain, Domain_ptr>("Domain")*

*   .def("set_solver" , &Domain::set_solver)*

*   .add_property("solver" , &Domain::solver)*

* ;*

*}*

The code compiles ok. The problem appears while running in Python:

*from test import *
**d = Domain()
**s = Solver()
**d.set_solver(s)    # is it ok to do that?
**d.solver.func()    # this line does not work*

With the following error message:

*Traceback (most recent call last):*
*  File "test_test.py", line 5, in <module>*
*    d.solver.func()*
*Boost.Python.ArgumentError: Python argument types in*
*    Solver.func(Solver)*
*did not match C++ signature:*
*    func(Solver {lvalue})*

I suspect that the problem is related with add_property returning a
shared_ptr<Solver> aka Solver_ptr.
It seems that add_property is returning a *non lvalue* Solver object.
I tried applying return value policies with no luck.
How can I get Domain::solver with type Solver_ptr in Python as a lvalue ?

Thanks!

Raul Durand