Python threading loop not continuing?

Question

I'm trying to write a simple program where a timer runs in the background, and every time the timer hits 0, a new image opens up and the timer resets again, for it to continue on and on.

import time
from PIL import Image
import random
import os
import threading

t_time = 5   # seconds i'd like to wait

def Countdown():
    global t_time
    if t_time > 0:
        for i in range(5):
            t_time -= 1
            time.sleep(1)
            print (t_time)


countdown_thread = threading.Thread(target=Countdown)

countdown_thread.start()

def AnmuViewer():
    global t_time

    if t_time > 0:
        random_pic = (random.choice(os.listdir("D:/de_clutter/memez/anmu")))
        openPic = Image.open('D:/de_clutter/memez/anmu/' + random_pic)
        openPic.show()
    if t_time == 0:
            t_time = 5      # theoretically this should reset t_time to 5,
                            # causing Countdown() to start over again. but doesn't

AnmuViewer_thread = threading.Thread(target=AnmuViewer)
AnmuViewer_thread.start()

Instead, the image pops up, the counter counts down to 0, then the program ends.

Answer 1

You're not protecting the shared variable t_time in any way so you are always risking race conditions. Given the sleep calls it would probably work itself out except Anmuviewer isn't a loop. So you start a thread that immediately counts down t_time by one then Amnuviewer runs and it shows a picture then the second if fails and Anmuviewer ends. If you replace Anmuviewer with:

def AnmuViewer():
    global t_time
    while True:
        if t_time <= 0:
            random_pic = (random.choice(os.listdir("D:/de_clutter/memez/anmu")))
            openPic = Image.open('D:/de_clutter/memez/anmu/' + random_pic)
            openPic.show()
            t_time = 5
        sleep(0.5)

that is probably what you're after and will likely work reliably due to how long the sleep calls are though it could still have race conditions.