From http://www.boost.org/doc/libs/1_37_0/libs/python/doc/v2/overloads.html

Few methods and functions have parameters by default.

To send this information to boost::python, you need to call theses instructions :

BOOST_PYTHON_FUNCTION_OVERLOADS( overloadsname , functionname , arg_minimum, arg_maximum )
BOOST_PYTHON_FUNCTION_OVERLOADS( overloadsname , classname::staticmethodname , arg_minimum, arg_maximum )

For global functions and for static methods.

BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS( overloadsname , classname::methodname, arg_minimum, arg_maximum )

For class methods.

Sample :

#include <boost/python/module.hpp>
#include <boost/python/def.hpp>
#include <boost/python/args.hpp>
#include <boost/python/tuple.hpp>
#include <boost/python/class.hpp>
#include <boost/python/overloads.hpp>
#include <boost/python/return_internal_reference.hpp>

using namespace boost::python;

tuple f(int x = 1, double y = 4.25, char const* z = "wow")
{
    return make_tuple(x, y, z);
}

BOOST_PYTHON_FUNCTION_OVERLOADS(f_overloads, f, 0, 3)

class X
{
    X( const int& _loc)
    {
       localval=_loc;
    }
    int returnsame(int x=5)
    {
        return x+localval;
    }
    static int returnsum(int m,int x=10)
    {
        return m+x;
    }
    int localval;
};

BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(X_returnsame_overloads, X::returnsame, 0, 1)
BOOST_PYTHON_FUNCTION_OVERLOADS(X_returnsum_overloads, X::returnsum, 1, 2)


BOOST_PYTHON_MODULE(args_ext)
{
    def("f", f, 
        f_overloads(
            args("x", "y", "z"), "This is f's docstring"
        ));

    
    class_<X>("X", init<int>())
        .def("returnsame", &X::returnsame, 
                X_returnsame_overloads(
                    args("x"), "returnsame's docstring"
                )
        )
        .def("returnsum", &X::returnsum,
                X_returnsum_overloads( args("x","m"), "returnsum's docstring"
               )
        )
        .staticmethod("returnsum")
        ;
}