Python - tkinter - thread (reddit.com)

#
# https://www.reddit.com/r/learnpython/comments/59nj50/while_loop_freezing_tkinter_gui_threading_issue/
# http://pastebin.com/q877u6gf
#

import tkinter as tk
import threading

# --- constants --- (UPPER_CASE)

START = 1
STOP  = 0
EXIT  = -1

# --- functions ---

def test_loop():
    global looping

    while True:
        if looping == START:
            print("test")
        if looping == EXIT:
            break

def start():
    global looping

    looping = START

def stop():
    global looping

    looping = STOP

# --- main ---

looping = STOP

root = tk.Tk()

text = tk.StringVar()
text.set("Here's some text!")

leftFrame = tk.Frame(root)
leftFrame.pack(side=tk.LEFT)

rightFrame = tk.Frame(root)
rightFrame.pack(side=tk.RIGHT)

playButton = tk.Button(leftFrame, text="Play", fg="blue", command=start)
playButton.pack(side=tk.TOP)

stopButton = tk.Button(rightFrame, text="Stop", fg="red", command=stop)
stopButton.pack(side=tk.BOTTOM)

message = tk.Message(root, textvariable=text, relief=tk.RAISED)
message.pack()

thread = threading.Thread(target=test_loop)
thread.daemon = True
thread.start()

root.mainloop()

looping = EXIT