from tkinter import *
def calculate():
try:
price = float(enter1.get())
a = 123000L
a = +123000L
a = -123000L
b = 123UL
c = 0x3aa4f
d = 0b1010101100
f = -3.14e+12
char = '\UAAFF34DD'
str = "ciao\r\n ehh\xAAs\u123456\U123456789ss\12345s"
tax = float(enter2.get())
percent = 100 * tax / price
result = "You paid %0.3f%s sales tax" % (percent, '%')
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()
root.geometry("200x150+30+30")
label1 = Label(root, text='Enter purchase price:')
label1.grid(row=0, column=0)
enter1 = Entry(root, bg='yellow')
enter1.grid(row=1, column=0)
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)
btn1 = Button(root, text='Calculate Percent', command=calculate)
btn1.grid(row=4, column=0)
label3 = Label(root)
label3.grid(row=5, column=0)
enter1.focus()
enter1.bind('<Return>', func=lambda e: enter2.focus_set())
root.mainloop()