def hook_wnd_proc(self):
        """Attach to OS Window message handler"""
        self.__local_wnd_proc_wrapped = WndProcType(self.local_wnd_proc)
        self.__old_wnd_proc = SetWindowLong(self.__local_win_handle,
                                        GWL_WNDPROC,
                                        self.__local_wnd_proc_wrapped)