how to exit a function when an event is set?

Question

I have an infinite loop thread that sets an event when a sensor is high/true

event  = threading.Event()

def eventSetter():
    while True:
        if sensor:
            event.set()
        else:
            event.clear()

th1 = threading.thread(target=eventSetter)
th1.start

and I have a function capture that takes 5 sec to execute

def capture():
    time.sleep(2) #sleep represents a task that takes 2 sec to finish
    time.sleep(1)
    time.sleep(2)
    return

now I want to exit the function capture in the middle of its task whenever the event is set

for example if task 1 takes 5sec to finish and the event occurs at time 2sec, the task should not continue at time 2sec and the function should exit

I tried checking for the event every line but i don’t know how to exit in the middle of its task thus it waits for the task to finish before return applies also I didn’t like the look of multiple if/return

def capture():
    time.sleep(2) #sleep represents a task that takes sec to finish
    if event.is_set():
        return
    time.sleep(1)
    if event.is_set():
        return
    time.sleep(2)
    if event.is_set():
        return

Asked By: Altz Kienn

||

Source

Answer 1

Do you want breaking loop ?

if you want break any time or condition you need to break `key.

for example

event  = threading.Event()
def eventSetter():
    while True:
        if sensor:
            event.set()
            break
            #loop stoped.
        else:
            event.clear()

     return True #or none.

Answered By: Underdeveloper

Answer 2

You’re going to have to check the event state every chance you get in order to break out of capture as soon as possible. The variation you provided is fine, but here are a couple other ways to do the same thing:

def capture():
    # nested checks are fine with only a few tasks but can get awkward
    # when the indentation gets too deep to be easily readable
    time.sleep(2) # task 1
    if not event.is_set()
        time.sleep(1) # task 2
        if not event.is_set():
            time.sleep(2) # task 3

def capture():
    # defining a list of functions to be executed is great when there
    # are many subtasks but can be overkill if there are just a few
    from functools import partial
    subtasks = [
        partial(time.sleep, 2), # first task
        partial(time.sleep, 1), # second task
        partial(time.sleep, 2)  # third task
    ]

    for subtask in subtasks:
        if event.is_set():
            return
        subtask()

Answered By: Woodford

how to exit a function when an event is set?

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