python
import toga
def button_handler(widget):
label.text = "Hello, Toga!"
def build(app):
box = toga.Box()
button = toga.Button('Click me!', on_press=button_handler)
box.add(button)
global label
label = toga.Label('Welcome to Toga!')
box.add(label)
return box
app = toga.App('MyApp', 'org.beeware.myapp', startup=build)
app.main_loop()
