Threads

import time
 
nb_repeat = 50
 
 
def a_complex_operation(*args):
    a = []
    for x in range(999999):
        a.append(x)
    return None
 
 
t1 = time.time()
for _ in range(nb_repeat):
    a_complex_operation()
print time.time()-t1


from multiprocessing import Pool
nb_repeat = 50
 
def a_complex_operation(*args):
    a = []
    for x in range(999999):
        a.append(x)
    return None
pool = Pool(processes=nb_repeat)
results = pool.map(a_complex_operation, [None for _ in range(nb_repeat)])


from threading import Thread
import time
 
nb_repeat = 50
 
def a_complex_operation(*args):
    a = []
    for x in range(999999):
        a.append(x)
    return None
 
t1 = time.time()
threads = []
for _ in range(nb_repeat):
    threads.append(Thread(target=a_complex_operation))
 
[x.start() for x in threads]
[x.join() for x in threads]
print time.time()-t1