django: while files are preparing for download , show loading animation

I use Django , When files are preparing for download , I want to show loading circle animation , How can i understand files preparing finish time ?

I try this code but its useless because it calculate is long for response

request.start_time = time.time() print("start") print(request.start_time) print("final") print(time.time()) total = time.time() - request.start_time print("total unclear") print(total) print("total") print(int(total * 1000))

No error