What you're looking for is AJAX. You can use this to query your server without reloading the page in the browser. When the page loads, you should grab a time object (using javascript) then every time someone commits their changes to Flask, record their time object along with the new contents. If the time object < the current, you'll need to compare the difference.

As far as reading items from a python list...you're going to need to figure out how you're returning the data from flask. If I were you, I would use the json module to encode your python data in json objects (similar to dictionaries) then return that to the calling browser; the reason is that json is a javascript native type.

You could also return a string and parse it on the client side.

Anyway, you can figure that out.

Flask and AJAX

JSON module

jQuery.ajax