What is the best way to stop a thread and avoid 'RuntimeError' in python using threading and tkinter modules?

Question

I have went through multiple solutions on the net, but they require a lot of code that might get confusing once you scale up. Is there a simple way to stop the thread and avoid the RuntimeError: threads can only be started once, in order to call the thread an infinite number of times. Here is a simple version of my code:

import tkinter
import time
import threading

def func():

    entry.config(state='disabled')
    label.configure(text="Standby for  seconds")
    time.sleep(3)
    sum = 0
    for i in range(int(entry.get())):
        time.sleep(0.5)
        sum = sum+i
        label.configure(text=str(sum))
    entry.config(state='normal')

mainwindow = tkinter.Tk()
mainwindow.title('Sum up to any number')

entry = tkinter.Entry(mainwindow)
entry.pack()
label = tkinter.Label(mainwindow, text = "Enter an integer",font=("Arial",33))
label.pack()

print(entry.get())

button = tkinter.Button(mainwindow, text="Press me", command=threading.Thread(target=func).start)
button.pack()

Answer 1

While this is a simple way that get things done, in a fewer lines of code. I couldn't use the .join() method. But, it seems that the app isn't creating any new threads. This is obvious through threading.active_counts() method. Here is the code below:

import tkinter, threading, time

def calc():
    entry.config(state='disabled')
    label.configure(text="Standby for 3 seconds")
    time.sleep(3)
    sum = 0
    for i in range(int(entry.get())):
        time.sleep(0.5)
        sum = sum+i
        labelnum.configure(text=str(sum))
    button.config(state='normal')
    label.configure(text="Sum up to any number")
    entry.config(state='normal')

def func():
    t = threading.Thread(target=calc)
    t.start()
    #del t
    print('Active threads:',threading.active_count())


mainwindow = tkinter.Tk()
mainwindow.title('Sum up to any number')
entry = tkinter.Entry(mainwindow)
entry.pack()
label = tkinter.Label(mainwindow, text = "Enter an integer",font=("Arial",33))
label.pack()
labelnum = tkinter.Label(mainwindow, text="",font=('Arial',33))
labelnum.pack()
button = tkinter.Button(mainwindow, text="Press me", command=func)
button.pack()
mainwindow.mainloop()