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

Question

I would like to return some data from c++ code as a numpy.array object. I had a look at boost::python::numeric, but its documentation is very terse

Answer 1

Doing it using the numpy api directly is not necessarily difficult, but I use boost::multiarray regularly for my projects and find it convenient to transfer the shapes of the array between the C++/Python boundary automatically. So, here is my recipe. Use http://code.google.com/p/numpy-boost/, or better yet, this version of the numpy_boost.hpp header; which is a better fit for multi-file boost::python projects, although it uses some C++11. Then, from your boost::python code, use something like this:

PyObject* myfunc(/*....*/)
{
   // If your data is already in a boost::multiarray object:
   // numpy_boost< double, 1 > to_python( numpy_from_boost_array(result_cm) );
   // otherwise:
   numpy_boost< double, 1> to_python( boost::extents[n] );
   std::copy( my_vector.begin(), my_vector.end(), to_python.begin() );

   PyObject* result = to_python.py_ptr();
   Py_INCREF( result );

   return result;
}