how to create a progress bar in python flask for a function call in html

Question

I wanted to run a python function when I click submit button on the index.html page, as the function takes a lot of time to run the page is getting timed out.

here is my code:

@app.route('/recommend/<search_keyword>')
def recommend(search_keyword):
    global urls
    urls=[]
    cmp='complete'
    urls=task(search_keyword)
    return render_template('index.html')

My function task() returns a list which is passed to the index.html page to display the list