Pickling a vector in boost python?

Question

I have this simple C++ code:

class Contained {};

class CannotPickle {
public:
    CannotPickle() {};
    CannotPickle(std::vector<boost::shared_ptr<Contained>> new_vector) 
      : my_vector(new_vector) {};
    std::vector<boost::shared_ptr<Contained>> my_vector;
};

struct CannotPickle_pickle_suite : boost::python::pickle_suite
{
    static
    boost::python::tuple
    getinitargs(CannotPickle const& c)
    {
        return boost::python::make_tuple(c.my_vector);
    }
};

I'm trying to enable pickling support for CannotPickle like this:

class_<Contained>("Contained");
class_<std::vector<boost::shared_ptr<Contained>>>("ContainedPtrList")
        .def(vector_indexing_suite<std::vector<boost::shared_ptr<Contained>>, true>());
class_<CannotPickle>("CannotPickle")
        .def_pickle(CannotPickle_pickle_suite());

When I try to actually call pickle on a CannotPickle I get this error: RuntimeError: Pickling of "MyModule.ContainedPtrList" instances is not enabled (http://www.boost.org/libs/python/doc/v2/pickle.html)

How can I enable pickling for a vector_indexing_suite?

Answer 1

Some additional searching yielded this code, which seems to work:

#include <vector>

#include <boost/python.hpp>
#include <boost/python/suite/indexing/vector_indexing_suite.hpp>
#include <boost/smart_ptr.hpp>
namespace py = boost::python;

template <class C>
struct PickleSuite: public py::pickle_suite { BOOST_STATIC_ASSERT(sizeof(C)==0); };

template <typename  T>
struct PickleSuite< std::vector<T> >: public py::pickle_suite
{
    static py::tuple getinitargs(const std::vector<T>& o)
    {
        return py::make_tuple();
    }

    static py::tuple getstate(py::object obj)
    {
        const std::vector<T>& o = py::extract<const std::vector<T>&>(obj)();

        return py::make_tuple(py::list(o));
    }

    static void setstate(py::object obj, py::tuple state)
    {
        std::vector<T>& o = py::extract<std::vector<T>&>(obj)();

        py::stl_input_iterator<typename std::vector<T>::value_type> begin(state[0]), end;
        o.insert(o.begin(),begin,end);
    }
};