Kivymd数学方程求解程序报错：AttributeError: 'super'对象无__getattr__属性

问题场景 #

开发基于Kivymd的数学方程求解程序，点击界面中的“Cal”或“Expand”按钮时，触发错误：

AttributeError: 'super' object has no attribute '__getattr__'

程序相关代码：

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.core.window import Window
from kivymd.uix.screen import MDScreen
from kivy.properties import DictProperty
from kivymd.uix.screenmanager import MDScreenManager

__version__ = "1.0.0"

kv = """WindowManager:
    Home:
    Heugebra:

<Home>:
    name: "Home"


    FloatLayout:
        orientation: "vertical"

        MDCard:
            size: 500,400

            FloatLayout:
                size: 500,400

                MDTextField:
                    id: Equ
                    hint_text: "Insert the Equation"
                    size_hint: None,None
                    width: 200
                    pos_hint: {"x": 0.3,"y": 0.3}
                    on_text_validate: root.get_data()
                MDLabel:
                    id: Eq_anser
                    text: "test"
                    pos_hint: {"x": 0.4,"y": 0.3}
                MDRoundFlatButton:
                    text: "Cal"
                    pos_hint: {"x": 0.8,"y": 0.3}
                    on_press: app.get_data()
                MDRoundFlatButton:
                    text: "Expand"
                    pos_hint: {"X": 0.4, "y": 0.3}
                    on_press: app.expand()
                MDRoundFlatButton:
                    text: "Draw"
                    pos_hint: {"x": 0.4,"y": 0.25}
                    on_release:
                        app.root.current = "Heugebra"
                        root.manager.transition.direction = "left"
                MDFloatingActionButtonSpeedDial:
                    data: app.data
                    root_button_anim: True
<Heugebra>:
    name: "Heugebra"

    MDRoundFlatButton:
        text: "Back to Home"
        pos_hint: {"x": 0.3, "Y": 0.5}
        on_release:
            app.root.current = "Home"
            root.manager.transition.direction = "right"

"""

class WindowManager(MDScreenManager):
    pass

class Home(MDScreen):
    pass

class Heugebra(MDScreen):
    pass

class MAIN(MDApp):
    data = DictProperty()

    def on_start(self):
        Window.set_title('Every Solver')

    def build(self):
        self.theme_cls.theme_style = "Dark"
        self.theme_cls.primary_palette = "Indigo"
        self.data = {
                "Integrate": ["math-integral",
                        "on_press", lambda x: self.calculas('int')],
                "Diff": ["math-diff.png",
                        "on_press", lambda x: self.calculas('diff')],
        }
        return Builder.load_string(kv)

    def calculas(self, calc: str):
        print(calc)

    def get_data(self):
        x = self.root.ids.Equ.text
        self.root.ids.Eq_anser.text = "None"

    def expand(self):
        x = self.root.ids.Equ.text
        self.root.ids.Eq_anser.text = "None"

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

错误原因 #

错误根源在于MAIN类的get_data和expand方法中，self.root指向的是WindowManager（屏幕管理器），而该组件并没有直接包含Equ和Eq_anser这两个控件的ids——这两个控件属于Home屏幕内部的元素，直接通过self.root.ids访问会找不到目标控件，从而触发__getattr__相关的属性错误。

另外，原代码中“Expand”按钮的pos_hint使用了大写的"X"，这不符合Kivy的属性命名规范（应为小写"x"），会导致布局异常，建议一并修正。

解决方法 #

方法一：在App类中获取目标屏幕实例后访问控件 #

修改MAIN类的get_data和expand方法，先通过屏幕管理器获取Home屏幕的实例，再通过实例访问内部ids：

def get_data(self):
    # 获取Home屏幕实例
    home_screen = self.root.get_screen("Home")
    x = home_screen.ids.Equ.text
    home_screen.ids.Eq_anser.text = "None"

def expand(self):
    home_screen = self.root.get_screen("Home")
    x = home_screen.ids.Equ.text
    home_screen.ids.Eq_anser.text = "None"

同时修正kv中Expand按钮的pos_hint：

MDRoundFlatButton:
    text: "Expand"
    pos_hint: {"x": 0.4, "y": 0.3}  # 将大写X改为小写x
    on_press: app.expand()

方法二：将逻辑迁移到Home屏幕类中（更符合Kivy的MVC设计） #

将数据获取和处理的逻辑放在Home屏幕类内部，直接通过self.ids访问控件，同时调整按钮的绑定事件：

1. 修改kv文件中的按钮绑定：

MDRoundFlatButton:
    text: "Cal"
    pos_hint: {"x": 0.8,"y": 0.3}
    on_press: root.get_data()  # 改为调用根布局（Home屏幕）的方法
MDRoundFlatButton:
    text: "Expand"
    pos_hint: {"x": 0.4, "y": 0.3}  # 修正大写X为小写x
    on_press: root.expand()

2. 更新Home类，添加对应的方法：

class Home(MDScreen):
    def get_data(self):
        x = self.ids.Equ.text
        self.ids.Eq_anser.text = "None"

    def expand(self):
        x = self.ids.Equ.text
        self.ids.Eq_anser.text = "None"

3. 删除MAIN类中的get_data和expand方法。

两种方法都能解决错误，方法二更贴合Kivy的组件设计思路，推荐使用。

内容的提问来源于stack exchange，提问作者Hashem Alsharif