在python中使用kivy编写一个加减法的简单计算器，详细代码给我一下

以下是一个简单的加减法计算器的Kivy代码： ``` from kivy.app import App from kivy.uix.boxlayout import BoxLayout from kivy.uix.button import Button from kivy.uix.label import Label class CalculatorApp(App): def build(self): self.equation = "" layout = BoxLayout(orientation='vertical') self.label = Label(text="0", font_size=50, size_hint=(1, 0.5)) layout.add_widget(self.label) button_layout = BoxLayout() buttons = [ ["7", "8", "9", "+"], ["4", "5", "6", "-"], ["1", "2", "3", "="], ["C", "0", ".", ""] ] for row in buttons: row_layout = BoxLayout() for label in row: button = Button(text=label, font_size=30, size_hint=(0.25, 0.25)) button.bind(on_press=self.button_pressed) row_layout.add_widget(button) button_layout.add_widget(row_layout) layout.add_widget(button_layout) return layout def button_pressed(self, instance): label = instance.text if label == "C": self.equation = "" self.label.text = "0" elif label == "=": try: result = str(eval(self.equation)) self.label.text = result self.equation = result except: self.label.text = "Error" self.equation = "" else: self.equation += label self.label.text = self.equation if __name__ == '__main__': CalculatorApp().run() ``` 这个计算器使用BoxLayout布局，包含一个Label和一个按钮布局。按钮布局包含四个行，每行包含四个按钮。当用户按下按钮时，它们的标签将添加到equation字符串中，并显示在Label上。如果用户按下“C”按钮，则清除equation字符串和Label。如果用户按下“=”按钮，则计算equation字符串的结果并显示在Label上。如果计算失败，则显示“Error”。