Deploying and running a Python Flask/Socketio webapp

I recently found this example about Flask and SocketIO, where some numbers are generated with a Python script, sent via Websocket to the frontend and are printed in real-time dynamically on a Web page.

I want to build a Webapp based on Flask/SocketIO and on this example, but since i am fairly new to Python, i had the following doubt:

Let's say i deploy that simple app somewhere where it runs 24/7, for example on Heroku. Will the app start working and printing numbers only when someone opens it on a browser, showing different numbers to each, or will it run for the whole time, showing the same thing to each one who opens it?