Example for SO question 41086402

#! /usr/bin/python3
from kivy.app import App
from kivy.uix.image import Image
from kivy.uix.widget import Widget
from kivy.uix.relativelayout import RelativeLayout
from kivy.core.window import Window
from kivy.graphics.context_instructions import Scale, PushMatrix, PopMatrix

class ActorWidget(Widget):
    """
    The actor widget that contains an actor image
    """
    def __init__(self, source='Chassis.png', **kwargs):
        super(ActorWidget, self).__init__(**kwargs)
        self.img = Image(source=source, size=(32, 32), allow_stretch=True)
        self.add_widget(self.img)
        self.bind(pos=self.update_img)
        self.bind(size=self.update_img)

    def update_img(self, a, b):
        self.img.pos = self.pos
        self.img.size = self.size

class DemoWidget(RelativeLayout):
    def __init__(self, wid, *args, **kwargs):
        super(DemoWidget, self).__init__(*args, **kwargs)
        self.wid = wid
        self.add_widget(self.wid)
        self._keyboard = Window.request_keyboard(self._keyboard_closed, self)
        self._keyboard.bind(on_key_down=self._on_key_down)

    def _keyboard_closed(self):
        self._keyboard.unbind(on_key_down=self.on_key_down)
        self._keyboard=None

    def _on_key_down(self, *args, **kwargs):
        print('Key accepted')  #  To see that it's not some keyboard issue
        self.wid.canvas.before.add(PushMatrix())
        self.wid.canvas.before.add(Scale(y=10.0))
        self.wid.canvas.after.add(PopMatrix())
        self.wid.canvas.ask_update
        
        
    
class TestApp(App):
    def __init__(self):
        super(TestApp,self).__init__()
        
    def build(self):
        root = DemoWidget(wid=ActorWidget(), size=(32,32), size_hint=(None, None))
        Window.size=(100, 100)
        return root
        
app = TestApp()
app.run()