class A:
    def __init__(self):
        documents = []
        doc_num   = 0

        self.main_window = gtk.Window(gtk.WINDOW_TOPLEVEL)
        self.main_window.set_size_request(800,600)
        self.main_window.set_position(gtk.WIN_POS_CENTER)	

        self.vbox = gtk.VBox(homogeneous = False, spacing = 0)
        
        self.init_menu()
        self.main_window.add(self.vbox)
        self.main_window.show_all()

    def init_menu(self):  
        self.main_menu = gtk.MenuBar()
        self.file_menu = gtk.Menu()
        self.file_item = gtk.MenuItem("File")
        self.file_item.set_submenu(self.file_menu)
        self.file_new = gtk.MenuItem("New")
        self.file_menu.append(self.file_new)
        
        self.menubox = gtk.VBox(homogeneous = False, spacing = 0)
        self.menubox.pack_start(self.main_menu, False,False, 0)
        self.vbox.pack_start(self.menubox, False, False, 0)
  
        self.menubox.show()

self.main_menu.append(self.file_item)