Kivy: dock demo without kv

dockdemonokv.py

import kivy
kivy.require('1.9.0')

from kivy.app import App
from kivy.uix.anchorlayout import AnchorLayout
from kivy.uix.stacklayout import StackLayout
from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.metrics import dp


class TestApp(App):
    def build(self):
        root = AnchorLayout(anchor_x='left')

        sl = StackLayout(orientation='lr-tb', size_hint=(None, None), width=1)
        sl.bind(minimum_height=sl.setter('height'))

        def update_button_size(inst, size):
            inst.width = size[0] + dp(12)
            inst.height = size[1] + dp(12)

        b1 = Button(text='Hello, this is a long message here', size_hint=(None, None))
        b1.bind(texture_size=update_button_size)

        b2 = Button(text='Hello world', size_hint=(None, None))
        b2.bind(texture_size=update_button_size)

        sep = Widget(size_hint_y=None, height=dp(12))

        b3 = Button(text='Bye', size_hint=(None, None))
        b3.bind(texture_size=update_button_size)

        sl.add_widget(b1)
        sl.add_widget(b2)
        sl.add_widget(sep)
        sl.add_widget(b3)

        root.add_widget(sl)

        return root

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