code: def _get_key(self, event):
      unikey = chr(Gdk.keyval_to_unicode(event.keyval))
      key = cbook._unikey_or_keysym_to_mplkey(
          unikey, Gdk.keyval_name(event.keyval)
      )
      mods = self._mpl_modifiers(event.state, exclude=key)
      if "shift" in mods and unikey.isprintable():
          mods.remove("shift")
      return "+".join([*mods, key])
  
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 15 for calling the FigureCanvasGTK3 obj's underlying member method code with example usage: obj._get_key(event) and returns: str