Main.py

import kivy
kivy.require('1.5.0')

import kivy.core.window
from kivy.config import Config
from kivy.app import App
from kivy.uix.floatlayout import FloatLayout

class MainUI(FloatLayout):
    pass

class MyApp(App):

    def build(self):
        Config.set('graphics', 'width', '1200')
        Config.set('graphics', 'height', '800')
        Config.write()
        print kivy.core.window.Window.size
        return MainUI()

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