I'm learning to use Tkinter and in the tutorials it tells me to import W from Tkinter, but W is just a str ("w").
My question is why use Tkinter.W not "w".  Is it because Tkinter will sometimes have the var equal something else dependent upon system?
I always use the string value. I see absolutely no benefit in using the constants. The chance of them changing is virtually zero. These constants have remained unchanged since Tkinter was created. 
tkinter takes backwards compatibility pretty seriously, so even if they are changed, the string values will undoubtedly continue to work for a year or two. 
My recommendation is to never use the constants.
Python Tkinter: Why use Tkinter.W not str "w"