code: def _add_button(self, button, group, position):
      if group not in self._groups:
          if self._groups:
              self._add_separator()
          toolbar = Gtk.Toolbar()
          toolbar.set_style(Gtk.ToolbarStyle.ICONS)
          self.pack_start(toolbar, False, False, 0)
          toolbar.show_all()
          self._groups[group] = toolbar
      self._groups[group].insert(button, position)
  
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 3 for calling the ToolbarGTK3 obj's underlying member method code with example usage: obj._add_button(button, group, position) without return types