Hello, If a free function 'func' has X* as its first argument, then, boost.python allows it to be bound to a member function on the python side, i.e., the following is legal: void func( X* x, arg1_t arg ) { ... } class_<X>( "X" ).def( "func", &func ); In order to use a function object in place of a free function, one must specialize/overload boost::python::detail::get_signature which, for some reason, does not account for function objects. Here's a very simple example that works: ---------------------------------------------- #include <boost/mpl/vector.hpp> struct X { int y; }; // Function object struct Z { int operator()( X *x, int z ) { return z + x->y; } }; namespace boost { namespace python { namespace detail { mpl::vector<int, X*, int> get_signature( Z&, X* ) {return mpl::vector<int, X*, int>();} }}} #include <boost/python/class.hpp> #include <boost/python/module.hpp> BOOST_PYTHON_MODULE( mft ) { boost::python::class_<X>( "X" ) .def( "z", Z() ).def_readwrite( "y", &X::y ); } ------------------------------------------------- However, note that the overload of get_signature precedes the inclusion of the boost.python headers, which is extremely inconvenient. However, if the headers are moved to their proper location as in the following, ---------------------------------------------- #include <boost/mpl/vector.hpp> #include <boost/python/class.hpp> #include <boost/python/module.hpp> struct X { int y; }; // Function object struct Z { int operator()( X *x, int z ) { return z + x->y; } }; namespace boost { namespace python { namespace detail { boost::mpl::vector<int, X*, int> get_signature( Z&, X* ) {return boost::mpl::vector<int, X*, int>();} }}} BOOST_PYTHON_MODULE( mft ) { boost::python::class_<X>( "X" ) .def( "z", Z() ).def_readwrite( "y", &X::y ); } ------------------------------------------------- the compilation fails with the following error message (gcc 4.4.1 with boost 1.37 or 1.39): $ g++ -Wall -shared -o mft.so memft.cc -lboost_python-mt - I/usr/include/python2.6 -fPIC In file included from memft.cc:1: /usr/include/boost/python/class.hpp: In member function ‘void boost::python::class_<T, X1, X2, X3>::def_impl(T*, const char*, Fn, const Helper&, ...) [with T = X, Fn = Z, Helper = boost::python::detail::def_helper<const char*, boost::python::detail::not_specified, boost::python::detail::not_specified, boost::python::detail::not_specified>, W = X, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]’: /usr/include/boost/python/class.hpp:235: instantiated from ‘boost::python::class_<T, X1, X2, X3>& boost::python::class_<T, X1, X2, X3>::def(const char*, F) [with F = Z, W = X, X1 = boost::python::detail::not_specified, X2 = boost::python::detail::not_specified, X3 = boost::python::detail::not_specified]’ memft.cc:16: instantiated from here /usr/include/boost/python/class.hpp:536: error: no matching function for call to ‘get_signature(Z&, X*)’ Why is the overloaded get_signature not picked up when it is declared *after* the inclusion of the headers? The reason for using function objects is to change the argument types of a member function of X as seen by python; for example, the functor would have an argument type 'double' and would then internally convert the received 'double' argument from the python side into some custom type prior to passing it to the member function of X. In other words, the functor would act as a C++ equivalent of a python decorator. Regards, Ravi