# a rather generic Tkinter GUI template for calculations
# uses Entry() for data input and Button() to start calculation
 
from Tkinter import *
 
def calculate():
    try:
        # get the enter1 and enter2 values
        price = float(enter1.get())
        tax = float(enter2.get())
        # do the calculation
        percent = 100 * tax / price
        result = "You paid %0.3f%s sales tax" % (percent, '%')
        # display the result string
        label3.config(text=result)
    except ValueError:
        label3.config(text='Enter numeric values!')
    except ZeroDivisionError:
        label3.config(text='Price can not be zero!')
        enter1.focus_set()
 
root = Tk()
# window geometry is width x height + x_offset + y_offset
root.geometry("200x150+30+30")
 
# first entry with label
label1 = Label(root, text='Enter purchase price:')
label1.grid(row=0, column=0)
enter1 = Entry(root, bg='yellow')
enter1.grid(row=1, column=0)
 
# second entry with label
label2 = Label(root, text='Enter sales tax paid:')
label2.grid(row=2, column=0)
enter2 = Entry(root, bg='yellow')
enter2.grid(row=3, column=0)
 
# do the calculation by clicking the button
btn1 = Button(root, text='Calculate Percent', command=calculate)
btn1.grid(row=4, column=0)
 
# display the result in this label
label3 = Label(root)
label3.grid(row=5, column=0)
 
# start cursor in enter1
enter1.focus()
# value has been entered in enter1 now switch focus to enter2
enter1.bind('<Return>', func=lambda e: enter2.focus_set())
 
root.mainloop()