Flask return nothing, instead of having the re-render template
If you want the user to stay in place, you should send the form using JavaScript asynchronously. That way, the browser won't try to fetch and render a new page.
You won't be able to get this behavior from the Flask end only. You can return effectively nothing but the browser will still try to get it and render that nothing for the client.
I have written a python function using flask framework to process some data submitted via a web form.  However I don't want to re-render the template, I really just want to process the data and the leave the web form, it the state it was in, when the POST request was created.  Not sure how to do this ... any suggestions ?