how to return numpy.array from boost::python?

arrays, boost-python, c++, numpy

Solution

UPDATE: the library described in my original answer (https://github.com/ndarray/Boost.NumPy) has been integrated directly into Boost.Python as of Boost 1.63, and hence the standalone version is now deprecated. The text below now corresponds to the new, integrated version (only the namespace has changed).

Boost.Python now includes a moderately complete wrapper of the NumPy C-API into a Boost.Python interface. It's pretty low-level, and mostly focused on how to address the more difficult problem of how to pass C++ data to and from NumPy without copying, but here's how you'd do a copied std::vector return with that:

#include "boost/python/numpy.hpp"

namespace bp = boost::python;
namespace bn = boost::python::numpy;

std::vector<double> myfunc(...);

bn::ndarray mywrapper(...) {
    std::vector<double> v = myfunc(...);
    Py_intptr_t shape[1] = { v.size() };
    bn::ndarray result = bn::zeros(1, shape, bn::dtype::get_builtin<double>());
    std::copy(v.begin(), v.end(), reinterpret_cast<double*>(result.get_data()));
    return result;
}

BOOST_PYTHON_MODULE(example) {
    bn::initialize();
    bp::def("myfunc", mywrapper);
}

Problem

Original source

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