A simple example of animating a graphical instruction of a widget from a keyboard event.

test_anim.py

from kivy.app import App
from kivy.animation import Animation
from kivy.lang import Builder
from kivy.properties import NumericProperty
from kivy.core.window import Window
from kivy.uix.boxlayout import BoxLayout


KV = '''
FloatLayout:
    MyWidget:
        id: widget
        size_hint: .5, .5
        pos_hint: {'center': (.5, .5)}

<MyWidget>:
    canvas.before:
        PushMatrix:
        Scale:
            origin: self.center
            xyz: [self.zoom, self.zoom, 1]
    canvas:
        Line:
            rectangle: self.pos + self.size
            width: 2

    canvas.after:
        PopMatrix:
'''


class MyWidget(BoxLayout):
    zoom = NumericProperty(1)


class MyApp(App):
    def build(self):
        self.root = Builder.load_string(KV)
        Window.bind(on_key_down=self.key_action)
        return self.root

    def key_action(self, *args):
        widget = self.root.ids.widget
        Animation.cancel_all(widget, 'zoom')
        anim = (
            Animation(zoom=.8, t='out_quad', d=.2)
            + Animation(zoom=1, t='out_elastic', d=.5)
        )

        anim.start(widget)


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