Here is a reminder why Boost::Python and C++ Templates in general are evil:
Quote from gcc error message:
In function `boost::python::api::object boost::python::detail::make_function_aux, boost::mpl::int_<0> >(void (pyPythonMsg::*)(int), boost::python::default_call_policies const&, boost::python::detail::args_from_python const&, boost::mpl::list3 const&, std::pair const&, boost::mpl::int_<0>)’: