Python question

a.py

import threading

c = 0 # counter

def inc():    
    global c
    c = c + 1

threads = list()

for index in range(4):    
    thr_id = threading.Thread(target=inc)
    threads.append(thr_id)

for t in threads:
    t.start()

print(c)

for t in threads:
    t.join()