Попытка проверить индекс текстового ввода текста, но получение ошибки

Question

Я пытаюсь проверить индекс текста Kivy TextInput, но он говорит мне, что индекс выходит за пределы диапазона. Вот мой код.

        self.creditCardField = TextInput(size_hint = (.6, .07), pos_hint = {"center_x": 0.5, "center_y": 0.70}, font_name = "fonts/Qanelas-Light.otf")
        self.creditCardField.hint_text = "Card Number"
        self.creditCardField.input_filter = 'int'
        self.add_widget(self.creditCardField)
        self.creditCardField.bind(text = self.on_text_card)
        self.creditCardField.bind(text = self.verification)
        self.creditCardImage = Image(pos_hint = {"center_x": 0.80, "center_y": 0.70})
        self.add_widget(self.creditCardImage)

    def verification(self, instance, value):
        if value[0] == "4":
            self.creditCardImage.source = "cardicons/visa.png"
        if value[0] == 5 and value[1] < 6 and value[1] > 0:
            self.creditCardImage.source = "cardicons/mastercard.png"
        if value[0:2] in (36, 38):
            self.creditCardImage.source = "cardicons/dinersclub.png"
        if value[0:4] == 6011 or value[0:2] == 65:
            self.creditCardImage.source = "cardicons/discover.png"
        if value[0:2] == 35:
            self.creditCardImage.source = "cardicons/jcb.png"
        if value[0:2] in (34, 37):
            self.creditCardImage.source = "cardicons/americanexpress.png"

Спасибо за помощь