Kivy 基础知识问题（prolly .kv 文件）

问：

你们能看看我的python/kivy代码吗？

main.py（复制自视频教程）：

from kivy.app import App
from kivy.uix.widget import Widget

class MainWidget(Widget):
    pass

class TheLabApp(App):
    pass

TheLabApp().run()

thelab.kv：

#:kivy ! 2.1.0

MainWidget:

<MainWidget>:
    Button:
        text: "Hello"
        size: "200dp", "100dp"
        pos: "100dp", "200dp"

运行此代码最终会得到不同的结果。有时它会编译返回空窗口，有时它最终会出现以下（或类似）错误：

 Traceback (most recent call last):
   File "c:\Users\klaud\Documents\Studia\A Python\test\main.py", line 10, in <module>
     TheLabApp().run()
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\app.py", line 954, in run
     self._run_prepare()
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\app.py", line 923, in _run_prepare
     self.load_kv(filename=self.kv_file)
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\app.py", line 696, in load_kv
     root = Builder.load_file(rfilename)
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\lang\builder.py", line 305, in load_file
     return self.load_string(data, **kwargs)
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\lang\builder.py", line 372, in load_string
     parser = Parser(content=string, filename=fn)
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\lang\parser.py", line 483, in __init__
     self.parse(content)
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\lang\parser.py", line 590, in parse
     self.execute_directives()
   File "C:\Users\klaud\AppData\Roaming\Python\Python310\site-packages\kivy\lang\parser.py", line 569, in execute_directives
     raise ParserException(self, ln, 'Unknown directive')
 kivy.lang.parser.ParserException: Parser: File "c:\Users\klaud\Documents\Studia\A Python\test\thelab.kv", line 1:
 ...
 >>    1:#:kivy
       2:
       3:MainWidget:
 ...
 Unknown directive

代码是从 yt 复制的，在那里它工作得很好。你有什么想法吗？