如何通过另一个函数更改on_press函数？ （蟒，kivy）

Question

我正在编程货币转换器只是为了好玩并学习更多关于python的东西。我试图通过＆＃34; swap＆＃34; -button的on_press函数来改变＆＃34;计算＆＃34; - 按钮的on_press函数。有了这个，我试图改变计算的方向。 这是代码： 蟒-文件：

class Waehrungsrechner(BoxLayout):    
    def swap_GBP(self,*args):
        GBP_textleft = self.ids.GBP_textleft
        GBP_textright = self.ids.GBP_textright
        textleft = GBP_textleft.text
        textright = GBP_textright.text
        BTN_calc = self.ids.GBP_calc

        direction = -1

        if textleft == "Euro":
            direction = 1
        elif textleft == "Britisches Pfund":
            direction = 2

        if direction == 1:
            GBP_textleft.text = "Britisches Pfund"
            GBP_textright.text = "Euro"
            BTN_calc.bind(on_press = Waehrungsrechner.calculate_GBP2())
            direction = 2
        elif direction == 2:
            GBP_textleft.text = "Euro"
            GBP_textright.text = "Britisches Pfund"
            BTN_calc.bind(on_press = Waehrungsrechner.calculate_GBP1())
            direction = 1


    def calculate_GBP1(self,*args):

        Input = self.ids.GBP_Input
        label = self.ids.GBP_Ergebnis
        access = True
        try:
            Eingabe = float(Input.text)
        except:
            label.text = "Error"
            access = False

        if access == True:
            Ergebnis = "{0:.2f}".format(Eingabe*GBP_valuef)
            label.text = str(Ergebnis)

    def calculate_GBP2(self,*args):

        Input = self.ids.GBP_Input
        label = self.ids.GBP_Ergebnis
        access = True
        try:
            Eingabe = float(Input.text)
        except:
            label.text = "Error"
            access = False

        if access == True:
            Ergebnis = "{0:.2f}".format(Eingabe*(1/GBP_valuef))
            label.text = str(Ergebnis)


class WaehrungsrechnerApp(App):

    def build(self):

        return Waehrungsrechner();

Waehrungsrechner1 = WaehrungsrechnerApp()
Waehrungsrechner1.run()

KV-文件：

<Waehrungsrechner>:
    orientation: 'vertical'

    Label:
        text: "Waehrungsrechner"
        font_size: 60
        size_hint_y: None
        height: 200


    BoxLayout:
        orientation: 'horizontal'

        BoxLayout:
            orientation: 'vertical'

            Label:
                id: GBP_textleft
                text: "Euro"
                font_size: 30

            TextInput:
                id: GBP_Input
                font_size: 25
                multiline: False

        BoxLayout:
            orientation: 'vertical'

            Button:
                id: GBP_calc
                text: "Berechne"
                font_size : 20
                on_press: root.calculate_GBP1()

            Button:
                text: "<-->"
                font_size: 20
                on_press: root.swap_GBP()

        BoxLayout:
            orientation: 'vertical'         

            Label:
                id: GBP_textright
                text: "Britisches Pfund"
                font_size: 30

            Label:
                id: GBP_Ergebnis
                text: ""
                font_size: 30

    TextInput:
        font_size: 30
        multiline: False

它显示：calculate_GBP2（）缺少1个必需的位置参数：＆＃39; self＆＃39;

Answer 1

必须通过对象访问类的方法，在您的情况下是self，除非它是staticmethod，此外，bind()方法需要名称函数，而不是评估函数，因此它消除了括号。

你必须改变：

BTN_calc.bind(on_press = Waehrungsrechner.calculate_GBP2())
...
BTN_calc.bind(on_press = Waehrungsrechner.calculate_GBP1())

为：

BTN_calc.bind(on_press = self.calculate_GBP2)
...
BTN_calc.bind(on_press = self.calculate_GBP1)

Answer 2

它似乎现在正在使用这两个函数，第一个是覆盖第二个函数的结果（添加打印时）。如何从按钮取消绑定功能？