Traceback after a kivy run

Question

I am just learning kivy. I wrote a few lines and I tried to run. To many errors: Code:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

class mainWindow(BoxLayout):
    pass


class mainApp(App):
    def build(self):
        return mainWindow

app=mainApp()
app.run()

Errors:

[INFO   ] [Logger      ] Record log in C:\Users\Salvatore Pennisi\.kivy\logs\kivy_21-10-02_44.txt
[INFO   ] [deps        ] Successfully imported "kivy_deps.angle" 0.3.0
[INFO   ] [deps        ] Successfully imported "kivy_deps.glew" 0.3.0
[INFO   ] [deps        ] Successfully imported "kivy_deps.sdl2" 0.3.1
[INFO   ] [Kivy        ] v2.0.0
[INFO   ] [Kivy        ] Installed at "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\__init__.py"
[INFO   ] [Python      ] v3.9.7 (tags/v3.9.7:1016ef3, Aug 30 2021, 20:19:38) [MSC v.1929 64 bit (AMD64)]
[INFO   ] [Python      ] Interpreter at "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\python.exe"
[INFO   ] [Factory     ] 186 symbols loaded
[INFO   ] [Image       ] Providers: img_tex, img_dds, img_sdl2, img_pil (img_ffpyplayer ignored)
 Traceback (most recent call last):
   File "c:\Users\Salvatore Pennisi\Desktop\Personal Home\Lavoro - progetti-studio\programmazione\Traduttore documenti\main.py", line 78, in <module>
     app.run()
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\app.py", line 949, in run
     self._run_prepare()
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\app.py", line 918, in _run_prepare
     self.load_kv(filename=self.kv_file)
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\app.py", line 691, in load_kv
     root = Builder.load_file(rfilename)
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\lang\builder.py", line 306, in load_file
     return self.load_string(data, **kwargs)
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\lang\builder.py", line 404, in load_string
     widget = Factory.get(parser.root.name)(__no_builder=True)
   File "C:\Users\Salvatore Pennisi\AppData\Local\Programs\Python\Python39\lib\site-packages\kivy\factory.py", line 144, in __getattr__
     raise AttributeError(
 AttributeError: First letter of class name <import kivy> is in lowercase

What am I doing wrong? I'd like to made a simple window and then add some features.

Answer 1

The build() method must return an instance of a widget, but return mainWindow is returning a class. Try changing that line to:

return mainWindow()

Also, your class names should start with a capital letter.