[python] Send data from a textbox into Flask?

Assuming you already know how to write a view in Flask that responds to a url, create one that reads the request.post data. To add the input box to this post data create a form on your page with the text box. You can then use jquery to do

var data = $('#<form-id>').serialize()

and then post to your view asynchronously using something like the below.

$.post('<your view url>', function(data) {
  $('.result').html(data);
});