python sleep function not working in thread code example

Example: sleep in python 3

#!/usr/bin/python3
import time

print ("Start : %s" % time.ctime())
time.sleep( 5 )
print ("End : %s" % time.ctime())

# Start : Mon Feb 15 12:08:42 2016
# End : Mon Feb 15 12:08:47 2016