boost::python: Python list to std::vector

Question

Finally I'm able to use std::vector in python using the [] operator. The trick is to simple provide a container in the boost C++ wrapper which handles the internal vector stuff:

#include <boost/python.hpp>
#include <vector>
class world
{
    std::vector<double> myvec;

    void add(double n)
    {
        this->myvec.push_back(n);
    }

    std::vector<double> show()
    {
     return this->myvec;
    }
};

BOOST_PYTHON_MODULE(hello)
{
    class_<std::vector<double> >("double_vector")
        .def(vector_indexing_suite<std::vector<double> >())
    ;

    class_<World>("World")
     .def("show", &World::show)
        .def("add", &World::add)
    ;
 }

The other challenge is: Howto translate python lists into std::vectors? I tried to add a c++ class expecting a std::vector as parameter and added the corresponding wrapper code:

#include <boost/python.hpp>
#include <vector>
class world
{
    std::vector<double> myvec;

    void add(double n)
    {
        this->myvec.push_back(n);
    }

    void massadd(std::vector<double> ns)
    {
        // Append ns to this->myvec
    }

    std::vector<double> show()
    {
     return this->myvec;
    }
};

BOOST_PYTHON_MODULE(hello)
{
    class_<std::vector<double> >("double_vector")
        .def(vector_indexing_suite<std::vector<double> >())
    ;

    class_<World>("World")
     .def("show", &World::show)
        .def("add", &World::add)
        .def("massadd", &World::massadd)
    ;
 }

But if doing so, I end up with the following Boost.Python.ArgumentError:

>>> w.massadd([2.0,3.0])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Boost.Python.ArgumentError: Python argument types in
    World.massadd(World, list)
did not match C++ signature:
    massadd(World {lvalue}, std::vector<double, std::allocator<double> >)

Can anybody tell me how I can access python lists within my c++ function?

Thanks, Daniel

Answer 1

To make your C++ method accept Python lists you should use boost::python::list

void massadd(boost::python::list& ns)
{
    for (int i = 0; i < len(ns); ++i)
    {
        add(boost::python::extract<double>(ns[i]));
    }
}