AttributeError: 'NoneType' object has no attribute 'get'

[George87]

Hi. I make my first steps on programming and i try to learn Python and Tkinter. I want to make a simple calc that has 2 entries and when i press the sum button make the sum and print the result on a label. The problem is that i get this error:

AttributeError: 'NoneType' object has no attribute 'get'

What i do wrong?

from tkinter import *

root = Tk()

def sum():
    result = Label (root, text=int(entry1.get()) + int(entry2.get())).pack()

entry1 = Entry(root).pack()
entry2 = Entry(root).pack()

sumbutton = Button (root, text="+", command=sum).pack()

root.mainloop()