app.py

from h2o_wave import main, app, Q, ui


@app('/')
async def serve(q: Q):
    # Check if a link is clicked or active in URL.
    if q.args['#'] is not None:
        # Set it to local state.
        q.client.current_nav = f'#{q.args["#"]}'

    # Create a navigation card.
    q.page['nav'] = ui.nav_card(
        box='1 1 2 -1',
        # Use saved value or go for a default.
        value=q.client.current_nav or '#menu/spam',
        title='H2O Wave',
        items=[
            ui.nav_group('Menu', items=[
                ui.nav_item(name='#menu/spam', label='Spam'),
                ui.nav_item(name='#menu/ham', label='Ham'),
                ui.nav_item(name='#menu/eggs', label='Eggs'),
                ui.nav_item(name='#menu/toast', label='Toast'),
            ])
        ]
    )

    await q.page.save()