无效语法 - kivy

Question

Learning kivy for the first time and faced a problem while starting .kv file.

main.py :

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

class Grid(Widget):
    pass

class App(App):
    def build(self):
        return Grid()

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

file.kv :

#:kivy 2.0.0
<Grid>:
    Label:
        text: "Hello World!"

error code :

Traceback (most recent call last):
  File "C:\Users\megaa\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\megaa\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "c:\Users\megaa\.vscode\extensions\ms-python.python-2020.12.424452561\pythonFiles\lib\python\debugpy\__main__.py", line 45, in <module>
    cli.main()
  File "c:\Users\megaa\.vscode\extensions\ms-python.python-2020.12.424452561\pythonFiles\lib\python\debugpy/..\debugpy\server\cli.py", line 444, in main        
    run()
  File "c:\Users\megaa\.vscode\extensions\ms-python.python-2020.12.424452561\pythonFiles\lib\python\debugpy/..\debugpy\server\cli.py", line 285, in run_file    
    runpy.run_path(target_as_str, run_name=compat.force_str("__main__"))
  File "C:\Users\megaa\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 267, in run_path
    code, fname = _get_code_from_file(run_name, path_name)
  File "C:\Users\megaa\AppData\Local\Programs\Python\Python39\lib\runpy.py", line 242, in _get_code_from_file
    code = compile(f.read(), fname, 'exec')
  File "d:\python\kivy\tutorial\tutorial2\file.kv", line 1
    <Grid>:
    ^
SyntaxError: invalid syntax

Answer 1

Remember that your.kv file is an design file. we have to load it in the python script.

In order to do that, Please do following in main.py

import kivy
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.gridlayout import GridLayout
from kivy.lang import Builder # new line added 

class Grid(Widget):
    pass

class App(App):
    def build(self):
        return Builder.load_file('file.kv') # change here

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

Now.kv file is loaded and should provide expected output.

Happy Learning

Edit 1:

Remove brackets and it should be running. In file.kv

#:kivy 2.0.0
Grid:
    GridLayout:
        cols: 1
        size: root.width, root.height

        Label:
            text: "Hello World!"

Edit 2: My main.py file:

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder # new line added 

class Grid(Widget):
    pass

class App(App):
    def build(self):
        return Builder.load_file('file.kv') # change here

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

Output Kivy window: :[output_kivy_window][https.//imgur.com/a/819K20A]