gistfile1.py

from kivy.app import App
from kivy.lang import Builder

from kivy.graphics import Color, Rectangle
from kivy.properties import ObjectProperty
from kivy.uix.behaviors import ButtonBehavior

from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.scrollview import ScrollView
from kivy.uix.image import Image
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.widget import Widget

Builder.load_string('''
<Main_Class>:
    Screen:
        FloatLayout:
            ScrollView:
                Image:
                    FloatLayout:
                        Button:
                            text: 'Hi'
                            id: butt
                        Second_Class:
                            size_hint: 0.5,0.5
                            main__class: root
<Second_Class>:
    on_release: self.function()
    canvas:
        Color:
            rgba: 1,0,0,1
        Rectangle:
            size: self.size
            pos: self.pos
''')

class Second_Class(ButtonBehavior, Widget):
    main__class = ObjectProperty()

    def function(self):
        print self.main__class.ids.butt.text
    

class Main_Class(ScreenManager): 
    def __init__(self, **kwargs):
        super(Main_Class, self).__init__(**kwargs)

class Application(App):
    def build(self):
        return Main_Class()

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