问Kivy -如何从有/没有修饰符的按键中获得正确的字符？

EN

from kivy.app import App
from kivy.uix.floatlayout import FloatLayout
from kivy.properties import StringProperty
from kivy.core.window import Window, Keyboard
from kivy.logger import Logger

class textInsert(FloatLayout):
    def __init__(self, **kwargs):
        super(textInsert, self).__init__(**kwargs)
        self.super = []

        text = StringProperty()

        ########################################
        keyboard = Window.request_keyboard(self._keyboard_released, self)
        keyboard.bind(on_key_down=self._keyboard_on_key_down, on_key_up=self._keyboard_released)

        ########################################
    #end def __init__

    def _keyboard_released(self, window, keycode):
        self.super = []

    def _keyboard_on_key_down(self, window, keycode, text, super):
        if 'lctrl' in self.super and keycode[1] == 's':
            Logger.info("Item saved, {}".format(self.super))
            self.super = []
            return False
        elif 'lctrl' not in self.super and keycode[1] in ["lctrl"]:
            self.super.append(keycode[1])
            return False
        else:
            Logger.info("key {} pressed.".format(keycode))
            return False


class ROOT(App):
   def build(self):
      return textInsert()

if __name__ == '__main__':
   ROOT().run()