def __init__(self,**kwargs):
self.register_event_type('on_finish')
self.register_event_type('on_answer')
super(Exam, self).__init__(**kwargs)
self.orientation="vertical"
self.question_label=Label()
self.chain_widget=Caterpillar()
buttons=BoxLayout(orientation="horizontal")
b=Button(text="Valid")
b.background_color=(0,1,0,1)
b.val=True
b.bind(on_press=self.answer)
buttons.add_widget(b)
b=Button(text="Invalid")
b.background_color=(1,0,0,1)
b.val=False
b.bind(on_press=self.answer)
buttons.add_widget(b)
self.add_widget(self.question_label)
self.add_widget(self.chain_widget)
self.add_widget(buttons)
