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

Question

I have a method in c++ that gets called from python and needs to return a python list object.

I have already created the method, and its attached to an exposed class

Answer 1

I use following utility functions to convert from/to stl containers. The trivial sum function illustrates how they are used. Also I found following opensource package which has quite a few conversion utilities: https://github.com/cctbx/cctbx_project/tree/master/scitbx/boost_python

#include 
#include 
#include 
#include 

namespace bpy = boost::python;

namespace fm {

template 
bpy::list stl2py(const Container& vec) {
  typedef typename Container::value_type T;
  bpy::list lst;
  std::for_each(vec.begin(), vec.end(), [&](const T& t) { lst.append(t); });
  return lst;
}

template 
void py2stl(const bpy::list& lst, Container& vec) {
  typedef typename Container::value_type T;
  bpy::stl_input_iterator beg(lst), end;
  std::for_each(beg, end, [&](const T& t) { vec.push_back(t); });
}

bpy::list sum(const bpy::list& lhs, const bpy::list& rhs) {
  std::vector lhsv;
  py2stl(lhs, lhsv);

  std::vector rhsv;
  py2stl(rhs, rhsv);

  std::vector result(lhsv.size(), 0.0);
  for (int i = 0; i < lhsv.size(); ++i) {
    result[i] = lhsv[i] + rhsv[i];
  }
  return stl2py(result);
}

} // namespace fm

BOOST_PYTHON_MODULE(fm)
{
  bpy::def("sum", &fm::sum);
}