kivy count down animation WIP

count-down.py

'''
    count down 3-2-1 w/ fade out to full transparency
'''

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.properties import NumericProperty
from kivy.animation import Animation

Builder.load_string('''
<CustomFloat>:
    Button:
        text: 'Click me to start'
        on_press: root.start_count_down()
        size_hint: (1,0.1)

<CustomLabel>:
    font_size: '42sp'
    size_hint: (0.75, 0.75) # (None, None)
    pos_hint: {'center_x': 0.5, 'center_y': 0.5}
    canvas.before:
        Color:
            rgba: 0.47, 0.65, 1.0, 1.0
        Rectangle:
            # self here refers to ??? the widget ??? (CustomLabel?!)
            pos: self.pos
            size: self.size
''')

class CustomFloat(FloatLayout):
    label_number = NumericProperty(3)

    def start_count_down(self):
        self.label_number = 3
        self.count_down()

    def count_down(self, animation=None, widget=None):
        my_label = CustomLabel(text=str(self.label_number), color=[1,1,1,1])

        self.add_widget(my_label)
        Animation.cancel_all(my_label)

        fade_to_color = [1,1,1,0]

        anim = Animation(color=fade_to_color, font_size=250.0,
                         duration=1.0, t='in_circ')

        if self.label_number > 1:
            anim.bind(on_complete=self.count_down)

        anim.start(my_label)

        self.label_number -= 1

class CustomLabel(Label):
    pass

class TestApp(App):

    def build(self):
        return CustomFloat()

TestApp().run()