code: def _add_separator(self):
      sep = Gtk.Separator()
      sep.set_property("orientation", Gtk.Orientation.VERTICAL)
      self.pack_start(sep, False, True, 0)
      sep.show_all()
  
imports: import functools
  import logging
  import os
  from pathlib import Path
  import matplotlib
  from matplotlib import _api, backend_tools, cbook
  from matplotlib.backend_bases import ToolContainerBase, CloseEvent, KeyEvent, LocationEvent, MouseEvent, ResizeEvent
  from gi.repository import Gio, GLib, GObject, Gtk, Gdk
  from .None import _backend_gtk
  from ._backend_gtk import _BackendGTK, _FigureCanvasGTK, _FigureManagerGTK, _NavigationToolbar2GTK, TimerGTK
label_desc: Use image node_id 7 for calling the ToolbarGTK3 obj's underlying member method code with example usage: obj._add_separator() without return types