fire event of text entered in textinput

#!/usr/bin/kivy
import kivy
kivy.require('1.7.2')

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.gridlayout import GridLayout
from kivy.uix.textinput import TextInput

Builder.load_string('''
<MenuScreen>:
    GridLayout:
        padding: 5
        spacing: 5
        cols: 1
        padding: root.width*0.1
        TextInput:
            on_text: root.val1()
''')

class MenuScreen(Screen):
    def val1(self):
        print "i am executed"

sm = ScreenManager()
menu = MenuScreen(name='menu')
sm.add_widget(menu)

class MainApp(App):
    def build(self):
        return sm

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