Kivy: DictProperty demo

dicttest.py

import kivy
kivy.require('1.9.0')

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

## Creating the property in Python
#from kivy.uix.boxlayout import BoxLayout
#class TestBox(BoxLayout):
#   data = DictProperty({'a': ''})

root = Builder.load_string('''
#TestBox:
BoxLayout:
    ## Creating the property in kv
    data: {'a': ''}
    Label:
        text: 'None' if not root.data['a'] else root.data['a']
    Button:
        text: 'set foo'
        on_release: root.data['a'] = 'foo'
    Button:
        text: 'set bar'
        on_release: root.data['a'] = 'bar'
''')

class TestApp(App):
    def build(self):
        return root

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