Question

I call to join , so i dont understand why the main thread print ‘End’ before all threaded were finished.
The output is :

End
Thread
Thread

Additional related question:
Just to make sure if is set daemon flag to true, is it mean that there is no meaning to call to join (because main can be finished when there are still daemon threads)?

#!/usr/bin/env python
import sys
import threading
from time import sleep

num_worker_threads = 2                  
threads = []   

def worker():
    sleep(1)
    print 'Thread'

for i in range(num_worker_threads):
     t = threading.Thread(target=worker)
     threads.append(t)
     t.start()
     t.join

print 'End'

Answer 1

Because you actually don’t call join. Replace:

t.join

with:

t.join()

The point is that t.join expression returns bound method object, and adding parentheses makes expression to be a method call.

Joining threads matters only for user threads, daemon threads will not block main thread to finish.