I have a use case where we have a C++ framework that is exposed through boost python. If I use a C++ factory to create objects, I want to always return the same python object once it is exposed. I've done this through a postcall policy, but I was wondering if there is a better way. Below is a simple example of my problem and my proposed solution. This works, with the only drawback that I create a PyObject* that I throw out every time. I do not want my framework (in this case, struct X) to know anything about python. Also, I'm familiar with "has_backed_reference" and using a heldType wrapper, but that would only apply to objects instantiated through python. struct X; std::map<std::string, boost::shared_ptr<X> > xmap; std::map<X*, PyObject*> xpymap; struct X // a container element { std::string id; std::string check; X(std::string s) : id(s) { } void printId() { std::cout << "ID is " << id << std::endl; } void change_string(std::string nstring) { check = nstring; } void print_string() { std::cout << "String is now: " << check << std::endl; } boost::shared_ptr<X> static XFactory(std::string val) { std::map<std::string,boost::shared_ptr<X> >::iterator it = xmap.find(val); if (it == xmap.end()) { boost::shared_ptr<X> nptr = boost::make_shared<X>(val); xmap[val] = nptr; return nptr; } return xmap[val]; } }; // Custom call policy to overwrite the postcall from C++ back to python // template <typename BasePolicy = boost::python::default_call_policies> struct carls_policy : BasePolicy { template <typename ArgumentPackage> PyObject* postcall(const ArgumentPackage& args, PyObject* result) { // Chain to base policy. result = BasePolicy::postcall(args, result); // Extract shared_ptr from result // boost::shared_ptr<X> xptr = boost::python::extract< boost::shared_ptr<X> >(result); if (!xptr) { return result; } std::map< X*, PyObject* >::iterator it = xpymap.find(xptr.get()); if (it == xpymap.end()) { xpymap[xptr.get()] = result; Py_INCREF(xpymap[xptr.get()]); // Increment to store in map } else { Py_DECREF(result); // Not needed anymore } Py_INCREF(xpymap[xptr.get()]); // Inremented to return to python return xpymap[xptr.get()]; } }; BOOST_PYTHON_MODULE(rvp) { boost::python::class_<X, boost::shared_ptr<X> > ("X", boost::python::no_init) .def("XFactory", &X::XFactory, carls_policy<>()).staticmethod("XFactory") .def("printId", &X::printId) .def("change_string", &X::change_string) .def("print_string", &X::print_string) ; } Implementation:

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import rvp x1 = rvp.X.XFactory('id1') x2 = rvp.X.XFactory('id2') x3 = rvp.X.XFactory('id1') x1 is x3 True

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