How to add a basic parameter to a class in Kivy?

I am using Kivy ScreenLayout and I want to know how to create a basic button which will appear in every Screen. For example:

<Scr1>:
    Button:
        pos: 500, 500
        size: 200, 100
        pos_hint: None, None
        text: "Button"
    #something else than in other screens
    
<Scr2>:
    Button:
        pos: 500, 500
        size: 200, 100
        pos_hint: None, None
        text: "Button"
    #something else than in other screens
    
<Scr3>:
    Button:
        pos: 500, 500
        size: 200, 100
        pos_hint: None, None
        text: "Button"
    #something else than in other screens

I don’t want to copy and paste the Button in every class, especially when I have more than 20 screens. Is there a way how can be the button added as a basic parameter to every class without copying? Thanks for any answer.

Answer

You can just use inheritance. Here is an example with two ways of using inheritance as you desire:

from kivy.app import App
from kivy.factory import Factory
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen, ScreenManager

kv = '''
<BaseScreen>:
    Button:
        pos: 500, 500
        size: 200, 100
        size_hint: None, None
        text: "Button"
        on_release: app.root.current='scr2'

<Scr1>:
    name: 'scr1'
    Label:
        text: 'Screen 1'

<Scr2@BaseScreen>:  # inheritance here
    name: 'scr2'
    Label:
        text: 'Screen 2'
'''


class BaseScreen(Screen):
    pass


class Scr1(BaseScreen):  # inheritance here
    pass


class TestApp(App):
    def build(self):
        Builder.load_string(kv)
        sm = ScreenManager()
        sm.add_widget(Scr1())
        sm.add_widget(Factory.Scr2())
        return sm

TestApp().run()