[Tutor] How do we create a GUI to run a simple calculation program in Python?

[Alex Kleider]

On 2017-04-04 12:12, Alan Gauld via Tutor wrote:
> On 04/04/17 17:55, Lisa Hasler Waters wrote:
> 
>> A middle school student of mine created a program to calculate simple 
>> and
>> compound interest. He built it in PyCharm EDU using a Mac running 
>> 10.11.6.
>> 
>> He would like to create a GUI to run this program. Please, can you 
>> advise
>> on how he could build this?
> 
> He could use Tkinter, or he could create an HTML screen and
> write a small server using a Framework like Flask.
> 
> Whatever he does he will need to dsepsarate his UI from his
> logic - a good programming skill regardless of UI.

Can anyone suggest a good tutorial that explains exactly what this means 
and how to achieve it?
(separate UI from logic I mean.)