threading_gui.py

#!/usr/bin/env python3

import tkinter as tk
from tkinter import simpledialog, messagebox
import threading, queue, time

root = tk.Tk()
root.withdraw()
thread_queue = queue.Queue()

def show_error(error):
  messagebox.showerror('ERROR', error, parent = root)

def main(thread_queue):
  while 1:
    print("Infinite Loop")
    time.sleep(3)
    print("Infinite Loop2")
    thread_queue.put({ 'call': 'show_error', 'error': 'porra' })
    time.sleep(5)

def probe_for_message():
  try:
    res = thread_queue.get(0)
    if res['call'] == 'show_error':
      show_error(res['error'])
  except queue.Empty:
    pass

  root.after(500, probe_for_message)

if __name__ == "__main__":
  main_thread = threading.Thread(target = main, args=(thread_queue, ))
  main_thread.start()

  root.after(500, probe_for_message)
  root.mainloop()