Python 3.x 如何使用屏幕上的按钮打开设备摄像头？奇异蟒蛇3

我是编程新手，自学对我打击很大。我现在正在学习python并创建一个项目应用程序来识别叶子特性，我使用Kivymd作为UI。我仍然对如何从另一个文件调用函数感到困惑？这是我的main.py：

class MainScreen(Screen):
    pass

class FileManagerScreen(Screen):
    pass

class SecondScreen(Screen):
    pass

sn = ScreenManager()
screen = Screen()

sn.add_widget(MainScreen(name='mainmenu'))
sn.add_widget(FileManagerScreen(name='fmanager'))
sn.add_widget(SecondScreen(name='secondscreen'))

class MainApp(MDApp):
    spath = 'directory'

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        Window.bind(on_keyboard=self.events)
        self.manager_open = False
        self.file_manager = MDFileManager(
            exit_manager=self.exit_manager,
            select_path=self.select_path,
            previous=True,
        )

    def build(self):
        self.theme_cls.primary_palette = "Green"
        self.theme_cls.theme_style = "Dark"
        screens = Builder.load_string(KV)
        return screens

    def file_manager_open(self):
        self.file_manager.show('/User/Downloads/Test_Images')  # output manager to the screen
        self.manager_open = True

    def select_path(self, path):
        '''It will be called when you click on the file name
        or the catalog selection button.

        :type path: str;
        :param path: path to the selected directory or file;
        '''

        self.exit_manager()
        toast(path)
        self.print_path(path)

    def print_path(self, path):
        self.spath = 'C:' + path
        self.root.ids.screen_manager.get_screen("fmanager").ids.dir_label.text = "Directory Updated"

    def exit_manager(self, *args):
        '''Called when the user reaches the root of the directory tree.'''

        self.manager_open = False
        self.file_manager.close()

    def events(self, instance, keyboard, keycode, text, modifiers):
        '''Called when buttons are pressed on the mobile device.'''

        if keyboard in (1001, 27):
            if self.manager_open:
                self.file_manager.back()
        return True

if __name__ == '__main__':
    MainApp().run()
    app = MainApp()
    text = app.spath

当我在fmanager屏幕上单击摄像头按钮时，我希望从另一个文件夹打开摄像头功能。这件事我已经坚持了一个月了。有人能帮忙吗？非常感谢