Please explain why programm would go into the if statement

Question

Below is a simple python code, which just prints the actual time/date with delay. I would be very grateful if someone can explain to me (as simply as possible) when and why the programm goes into the if statement (if exitFlag:) What is the statement? if exitFLag == True? Sry I don't understand this line.

I tried to copy the function with a similiar and simpler code. But here the programm won't go into the if statement. I hope someone can help me to understand the code better.

test = 0
counter = 10
while counter:
    if test:
        print("if-statement is called")
        break
    print("still in loop")
    counter -=1

import threading
import time


exitFlag = 0

class myThread(threading.Thread):
    def __init__(self, threadID, name, counter):        
        threading.Thread.__init__(self)                 
        self.threadID = threadID                        
        self.name = name
        self.counter = counter

    def run(self):                                      
        print("Starting " + self.name)
        print_time(self.name, self.counter, 5)          
        print("Exiting " + self.name)


def print_time(threadName, counter, delay):
    while counter:
        if exitFlag:                                   
            threadName.exit()
        time.sleep(delay)
        print("%s: %s" % (threadName, time.ctime(time.time())))
        counter -= 1


thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)

thread1.start()
thread2.start()
thread1.join()
thread2.join()

print("Exiting main thread")

[Python `while x:` statement](https://stackoverflow.com/questions/46045023/python-while-x-statement) is another effective duplicate, as is [Python evaluates 0 as false](https://stackoverflow.com/questions/12497199/python-evaluates-0-as-false). — Charles Duffy, Aug 20 '19 at 21:05
...either way, none of the code here will ever enter the `if exitFlag:` or `if test:` sections, because nothing in either section ever assigns truthy values to the tested variables. — Charles Duffy, Aug 20 '19 at 21:06

score -1 · Accepted Answer · answered Aug 20 '19 at 21:15

So in Truth Value Testing (when you check if something is true or false), you can use a lot of different values.

Python's Docs say you can use the following values to represent false:

None

False

zero of any numeric type, for example, 0, 0L, 0.0, 0j.

any empty sequence, for example, '', (), [].

any empty mapping, for example, {}.

instances of user-defined classes, if the class defines a __nonzero__() or __len__() method, when that method returns the integer zero or bool value False.

Anything else evaluates to true.

In this program, exitFlag is an integer. The code

if exitFlag:                                   
        threadName.exit()

is basically saying: "If exitFlag is not 0, exit the thread"

That being said, the code never seems to change exitFlag from 0, so this if statement will likely never be entered

Please explain why programm would go into the if statement

1 Answers1