Python Threading Timer and Event objects

Question

code:

from threading import Timer, Event
from time import sleep

def hello(e):
    print e
    print 'Inside......'
    while True:
        if e.isSet():
            print "hello_world"
            break

if __name__ == '__main__':
    e = Event()
    t = Timer(1, hello(e,))
    t.start()
    print e.isSet()
    sleep(2)
    e.set()
    print e.isSet()

Output:

 [root@localhost ~]# python test_event.py 
<threading._Event object at 0x7f440cbbc310>
Inside......

In the above code, I am trying to understand the Timer and, Event objects from python. If I run the above code, the Timer invokes the function hello() and it runs indefinitely. The main thread is not executing the line next to t.start(). What am I missing here??

Thanks.

Possible duplicate of threading.Timer()

RatDon
– RatDon

2018-01-29 06:49:50 +00:00
Commented Jan 29, 2018 at 6:49 — RatDon
– RatDon, Commented Jan 29, 2018 at 6:49

RatDon · Accepted Answer · 2018-01-29 06:53:12Z

2

In your code,

t = Timer(1, hello(e,))

Instead of passing arguments to the thread, you are calling the function before creating the thread. hello(e,) calls the function which waits for the event e to set. Since it's stuck in an infinite loop here and doesn't return from the function hello, the thread creation is not happening and e is never set.

Just change it to a valid thread creation:

t = Timer(1, hello, [e])

edited Jan 29, 2018 at 6:53

answered Jan 29, 2018 at 6:45

RatDon

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1 Comment

wonder Over a year ago

Thanks a lot for explaining it with clarity.

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