AttributeError: 'Button' object has no attribute 'number'

class MyGrid(GridLayout):
    def __init__(self, **kwargs):
        super(MyGrid, self).__init__(**kwargs)
        
        self.cols = 1
        self.add_widget(Label(text="Lotto Number Generator"))
        self.number = (Label(text=""))
        self.add_widget(self.number)
        self.button = (Button(text="Generate"))
        self.add_widget(self.button)
        self.button.bind(on_press=generate)

def generate(self):
    self.number.text = random.sample(range(1, 36),k=7)


class LottoGen(App):
    def build(self):
        return MyGrid()

LottoGen().run()