[Tkinter] Getting Input from Tkinter Entry

[reblark]

You are trying (adjusted code, line 5 for example) to get amount before it exists.
move the definitions for the entry textvariables (lines 20, 21, 22) before you try to access.
You must also set the values to something valid before access, example:

amount = StringVar()
amount.set('0')

I used this code for another project and it worked without setting the values, like "amount.set('0')