如何使用Kivy (Python)的输入进行计算

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.textinput import TextInput
from kivy.uix.label import Label

class CalculatorApp(App):
    def calculate(self, instance):
        try:
            result = eval(self.input.text)
            self.output.text = str(result)
        except:
            self.output.text = "Error"

    def build(self):
        layout = BoxLayout(orientation='vertical')
        self.input = TextInput()
        layout.add_widget(self.input)
        button = Button(text='Calculate')
        button.bind(on_press=self.calculate)
        layout.add_widget(button)
        self.output = Label()
        layout.add_widget(self.output)
        return layout

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

python calculator.py