python3 index.py

from app import (start, App)


app = App()

@app.route('/')         # action for route /
def route_index():      # function name should have prefix 'route_'
    # simple return 'Hello, World!' in browser
    return app.response.send('Hello, World!')


start(app, __name__)    # default run in port 8080

# or define your port
# start(app, __name__, port = 5000)