setState in python while loop

Question

I am new to python and I was trying this below code. I have some experience in web development where we have the "setState()" function. Do we have similar functionality in python.

below is my code:

running = True
def updaterunning():
    logger.info("running is set")
    running = False

def func_function4():
    logger.info("starting function 4")
    timeout = time.time() +10
    a=1
    while time.time() <= timeout:
        if running == True:
            logger.info("function 4 : %s", a)
            a+=1
            time.sleep(1)
            if a == 7:
                updaterunning()
    logger.info("exiting function 4")

f4 = threading.Thread(target = func_function4)
f4.start()

actual output:

2021-06-26 22:57:01,604 - starting function 4
2021-06-26 22:57:01,609 - function 4 : 1
2021-06-26 22:57:02,623 - function 4 : 2
2021-06-26 22:57:03,637 - function 4 : 3
2021-06-26 22:57:04,652 - function 4 : 4
2021-06-26 22:57:05,663 - function 4 : 5
2021-06-26 22:57:06,675 - function 4 : 6
2021-06-26 22:57:07,686 - running is set
2021-06-26 22:57:07,688 - function 4 : 7
2021-06-26 22:57:08,696 - function 4 : 8
2021-06-26 22:57:09,703 - function 4 : 9
2021-06-26 22:57:10,718 - function 4 : 10
2021-06-26 22:57:11,736 - exiting function 4

expected output:

2021-06-26 22:57:01,604 - starting function 4
2021-06-26 22:57:01,609 - function 4 : 1
2021-06-26 22:57:02,623 - function 4 : 2
2021-06-26 22:57:03,637 - function 4 : 3
2021-06-26 22:57:04,652 - function 4 : 4
2021-06-26 22:57:05,663 - function 4 : 5
2021-06-26 22:57:06,675 - function 4 : 6
2021-06-26 22:57:07,686 - running is set
2021-06-26 22:57:11,736 - exiting function 4

Here, once I set the running to False, I expect the If condition (If running == True) to fail and thus exiting the program. But it keeps on executing. This should be a simple one to fix but I am unaware of the functionality. Thanks for the help.

Why would the if condition exit the program on fail? You are just running code when running is True, not stopping the code when running is True. I think you meant to add this to the while loop instead of another if statement. — Ayush Garg, Jun 26 '21 at 17:55
You could break out from the loop instead of constantly calling an extra if statement. — nagyl, Jun 26 '21 at 17:56
@megargayu. Yes. I had tried that earlier and then split the conditions to check. But you are right. I have now added the If condition to the while loop so that it exits the loop when the condition fails. Thank you. — Raja, Jun 27 '21 at 11:04

score 1 · Accepted Answer · answered Jun 26 '21 at 17:57

When you do running = False in your updaterunning function, it's setting a local variable called running; the variable in the outer scope is not changed.

One way to address this is with globals, but a better solution IMO is to put this state into an object.

class ThingDoer:
    def __init__(self):
        self.running = False

    def updaterunning(self):
        logger.info("running is set")
        self.running = False

    def func_function4(self):
        logger.info("starting function 4")
        self.running = True
        timeout = time.time() +10
        a = 1
        while time.time() <= timeout:
            if self.running == True:
                logger.info("function 4 : %s", a)
                a+=1
                time.sleep(1)
                if a == 7:
                    self.updaterunning()
        logger.info("exiting function 4")

f4 = threading.Thread(target = ThingDoer().func_function4)
f4.start()

By putting this state in a class, you make it possible to have more than one ThingDoer operating in parallel without interfering with each other (which would lead to some very difficult-to-debug behavior), but if you want to only have a single piece of running state, you can also do that by having ThingDoer be a singleton.

setState in python while loop

1 Answers1