NAsync | Task Extension Methods to mimic the async-await syntax | Reactive Programming library

Below is my script on using asyncio to operate with tkinter and its ttk.Progressbar() widget. I derived it after referring to these references (1, 2, 3, 4, 5). I got the progessbar widget to work. But I can't seem to be able to cancel(stop) the asyncio Task object responsible for updating tkinter.Tk() that I have created to replace the usual Tk() event mainloop(). As such, I dont' see a command prompt or >>> prompt after the Tk() window is destroyed. How can I or should I terminate the task object root.update_task? I am using python 3.6. I was hoping loop.shutdown_asyncgens() could end the cancelled task but it did not. Why did it not work? Thank you.