Passing variable changes between threads in Python functions [Beginner]

Question

So I have this code:

import time
import threading

bar = False

def foo():
    while True:
        if bar == True:
            print "Success!"
        else:
            print "Not yet!"
    time.sleep(1)

def example():
    while True:
        time.sleep(5)
        bar = True

t1 = threading.Thread(target=foo)
t1.start()

t2 = threading.Thread(target=example)
t2.start()

I'm trying to understand why I can't get bar to = to true.. If so, then the other thread should see the change and write Success!

Answer 1

bar is a global variable. You should put global bar inside example():

def example():
    global bar
    while True:
        time.sleep(5)
        bar = True

• When reading a variable, it is first searched inside the function and if not found, outside. That's why it's not necessary to put global bar inside foo().
• When a variable is assigned a value, it is done locally inside the function unless the global statement has been used. That's why it's necessary to put global bar inside example()

Answer 2

You must specify 'bar' as global variable. Otherwise 'bar' is only considered as a local variable.

def example():
    global bar
    while True:
        time.sleep(5)
        bar = True