code: def save_figure(self, *args):
      dialog = Gtk.FileChooserDialog(
          title="Save the figure",
          parent=self.canvas.get_toplevel(),
          action=Gtk.FileChooserAction.SAVE,
          buttons=(
              Gtk.STOCK_CANCEL,
              Gtk.ResponseType.CANCEL,
              Gtk.STOCK_SAVE,
              Gtk.ResponseType.OK,
          ),
      )
      for (
          name,
          fmts,
      ) in self.canvas.get_supported_filetypes_grouped().items():
          ff = Gtk.FileFilter()
          ff.set_name(name)
          for fmt in fmts:
              ff.add_pattern(f"*.{fmt}")
          dialog.add_filter(ff)
          if self.canvas.get_default_filetype() in fmts:
              dialog.set_filter(ff)
  
      @functools.partial(dialog.connect, "notify::filter")
      def on_notify_filter(*args):
          name = dialog.get_filter().get_name()
          fmt = self.canvas.get_supported_filetypes_grouped()[name][0]
          dialog.set_current_name(
              str(
                  Path(dialog.get_current_name()).with_suffix(f".{fmt}")
              )
          )
  
      dialog.set_current_folder(mpl.rcParams["savefig.directory"])
      dialog.set_current_name(self.canvas.get_default_filename())
      dialog.set_do_overwrite_confirmation(True)
  
      response = dialog.run()
      fname = dialog.get_filename()
      ff = dialog.get_filter()  # Doesn't autoadjust to filename :/
      fmt = self.canvas.get_supported_filetypes_grouped()[
          ff.get_name()
      ][0]
      dialog.destroy()
      if response != Gtk.ResponseType.OK:
          return
      # Save dir for next time, unless empty str (which means use cwd).
      if mpl.rcParams["savefig.directory"]:
          mpl.rcParams["savefig.directory"] = os.path.dirname(fname)
      try:
          self.canvas.figure.savefig(fname, format=fmt)
      except Exception as e:
          dialog = Gtk.MessageDialog(
              parent=self.canvas.get_toplevel(),
              message_format=str(e),
              type=Gtk.MessageType.ERROR,
              buttons=Gtk.ButtonsType.OK,
          )
          dialog.run()
          dialog.destroy()
  
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 2 for calling the NavigationToolbar2GTK3 obj's underlying member method code with example usage: obj.save_figure() without return types