[C++-sig] easy method for converting boost::tuple to python tuple?

[David Abrahams]

Grant Goodyear <grant at grantgoodyear.org> writes:

> I have a c++ function that returns boost::tuple<double, float, int>.  From
> python I get the following when I try to access this function::
>
> No to_python (by-value) converter found for C++ type:
> boost::tuples::tuple<double, float, int, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type,
> boost::tuples::null_type, boost::tuples::null_type>
>
> Fair enough, I need to tell boost.python what to do.  Google provides
> the following link:
> http://mail.python.org/pipermail/c++-sig/2002-July/001722.html
> which is a tad dated.  Is there a simple way to tell boost.python
> how to perform the conversion?

http://www.boost.org/libs/python/doc/v2/to_python_converter.html

should set you on the right path.

  // Untested!
  #include <boost/python/tuple.hpp>
  #include <boost/python/module.hpp>
  #include <boost/python/refcount.hpp>


  namespace python = boost::python;
  namespace tuples = boost::tuples;

  namespace my
  {
    template <class H, class T>
    python::tuple tuple_to_python(tuples::cons<H,T> const& x)
    {
        return python::make_tuple(x) + my::tuple_to_python(x.tail);
    }

    python::tuple tuple_to_python(tuples::null_type)
    {
        return python::tuple();
    }

    template <class T>
    struct tupleconverter
    {
        static PyObject* convert(T const& x)
        {
            return python::incref(my::tuple_to_python(x).ptr());
        }
    };
  }

  BOOST_PYTHON_MODULE(whatever)
  {
      to_python_converter<my_tuple_type, tupleconverter<my_tuple_type> >();
  }

Something like this really should be in the library already, though,
shouldn't it?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com