from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.textinput import TextInput
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout

class TesztApp(App):
	def build(self):
		self.box = BoxLayout(orientation='vertical', spacing=20)
		self.lbl = Label(text='Érték', size_hint=(1.0,.5))
		self.txt = TextInput(hint_text='Ide írj', size_hint=(1.0,.1))
		self.btn = Button(text='Valami', on_press=self.csinal, size_hint=(1.0,.1))
		
		self.box.add_widget(self.lbl)
		self.box.add_widget(self.txt)
		self.box.add_widget(self.btn)
		return self.box
	def csinal(self, instance):
		self.txt.text = 'valami'
TesztApp().run()