Python threads run the example concurrently and sequentially

#-*- coding:utf-8 -*- 
import threading 
import time 
def fun(name, ls_name, front_thread = None): 
''''' 
 Thread startup function  
 through front_thread To use threads to run in order  
''' 
time.clock() 
time.sleep(2) 
#  if front_thread Where there is, there is front_thread When the run is complete, run the current thread  
if front_thread != None: 
front_thread.join() 
ls_name.append(name) 
print "thread %s : %s"% (name, time.clock()) 

if __name__ == '__main__': 
ls_result_name = [] 
ls_thread = [] 
time.clock() 
#  One by one, to start 1000 A thread  
for i in range(0,10): 
if len(ls_thread) == 0: 
t = threading.Thread(target=fun, args=(i,ls_result_name,None)) 
else: 
t = threading.Thread(target=fun, args=(i,ls_result_name,ls_thread[-1])) 
t.start() 
ls_thread.append(t) 

#  Wait for all threads to finish  
for t in ls_thread: 
t.join() 

print 'ls_result_name:', ls_result_name 
print "main thread:%s" % time.clock()

The running result is:
Thread 0, 1.99962006344
Thread 1:2.00000866032
Thread 2:2.00059113658
Thread 3:2.00080345407
Thread 4:2.00100068584
Thread 5:2.00119456523
Thread 6:2.00138593033
Thread 7:2.00166753037
Thread 8:2.00211758757
Thread 9:2.0024776892
Ls_result_name: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
The main thread: 2.003211302
More detailed use of threads can be referred to:
http://docs.python.org/library/threading.html
For a more detailed introduction of the time.clock module, please refer to:
http://blog.csdn.net/kiki113/archive/2009/03/28/4033017.aspx