code: def bind_global_key(conn, event_type, key_string, cb):
      
      root = conn.get_setup().roots[0].root
      return bind_key(conn, event_type, root, key_string, cb)
docs: An alias for ``bind_key(event_type, ROOT_WINDOW, key_string, cb)``.
      :param event_type: Either 'KeyPress' or 'KeyRelease'.
      :type event_type: str
      :param key_string: A string of the form 'Mod1-Control-a'.
                         Namely, a list of zero or more modifiers separated by
                         '-', followed by a single non-modifier key.
      :type key_string: str
      :param cb: A first class function with no parameters.
      :type cb: function
      :return: True if the binding was successful, False otherwise.
      :rtype: bool