Without the code decorator @operator this code throws an exception in the PyCharm

[mysorian]

This code should work as this is a standard way of writing code and running it. But if I delete the decorator @operator the code throws an exception. Is it because of the version I am using (2.3.1) or the PyCharm IDE?

`from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout

class MyButtonApp(App):
@Property
def build(self):
layout = BoxLayout(orientation='vertical')
button = Button(text="BUTTON")
layout.add_widget(button)
return layout

if name == 'main':
MyButtonApp().run()`