Getting tkinter to display output in a textbox

Question

I'm trying to create a small GUI that when the user enters a number into a text box, and it displays (as a label) whether it is a prime number or not.

The code I have currently "works" (as in no errors are displayed) but the label doesn't change.

The prime number code works in the python shell.

My code is as follows:

from tkinter import *

root = Tk()

label1 = Label( root, text="Enter Number")
E1 = Entry(root, bd =5)

def isPrime():
    entry1 = E1.get()
    entry1 = int(entry1)
    for d in range(2,entry1):
        if entry1 % d == 0:
            label1 = Label(root, text="Not prime")
            root.update_idletasks()
            break
    else:
        label1 = Label(root, text="Is prime")


submit = Button(root, text ="Submit", command = isPrime)
root.update_idletasks()

label1.pack()
E1.pack()
submit.pack(side =BOTTOM) 
root.mainloop()

Thanks for any help in advance, and please let me know if you'd like any more clarification about any issues. Thanks.

You are replacing the label with a new one, instead of changing the existing Label. You should do label1["text"] = "Is prime" for example. — Amit Gold
– Amit Gold, Commented Apr 25, 2016 at 13:51
@AmitGold if you know the answer you should not be clicking the "Add Comment" button to post the answer. — Tadhg McDonald-Jensen
– Tadhg McDonald-Jensen, Commented Apr 25, 2016 at 14:00
@linusg what would you recommend instead of Tkinter for making GUIs with python? — Tadhg McDonald-Jensen
– Tadhg McDonald-Jensen, Commented Apr 25, 2016 at 14:14
@TadhgMcDonald-Jensen I was reviewing so I didn't have the button. — Amit Gold
– Amit Gold, Commented Apr 25, 2016 at 14:17

Lafexlos · Accepted Answer · 2016-04-25 14:05:45Z

You are re-creating the label1 everytime you click on button. Also, you are not packing the one you are creating since that one is in local scope of isPrime() method.

If you want to change the text of the label, you should pass it as parameter to isPrime() and use .config(text="text here") or label["text"] = "text here".

def isPrime(lbl):
    entry1 = int(E1.get())
    for d in range(2,entry1):
        if entry1 % d == 0:
            lbl.config(text = "Not prime")
            break
    else:
        lbl["text"] = "Prime"

submit = Button(root, text ="Submit", command = lambda:isPrime(label1))

or you can make label1 global and change its text.

def isPrime():
    global label1
    entry1 = E1.get()
    entry1 = int(entry1)
    for d in range(2,entry1):
        if entry1 % d == 0:
            label1.config(text = "Not prime")
            break
    else:
        label1["text"] = "Prime"

submit = Button(root, text ="Submit", command = isPrime)

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