1st i tried working in a program that generates random pokemon so we can create teams to play in showdown. It looked like this

I am new to function in python.My requirement is
Select Main data file by user opening folder location using tkiter
Select Lookup file from location
Select common column from main data file.
select common column from lookup file
select multiple lookup columns separated by comma
and merge data and save file at desired location.

I want to get a directory with a function and use the obtained path in another function.
For example, I’m just giving a simple code sample.

I have 2 functions: one that opens a certain window with buttons, and the other one that does stuff that I need and closes a window.
It works fine if I defy second function within the first one, but I need them to be separate, and that’s the problem.