http://www.dotblogs.com.tw/rickyteng/archive/2013/11/06/126852.aspx

class entryExit(object):
def __init__(self, f): 
    print 'entry init enter' 
    self.f = f 
    print 'entry init exit'
def __call__(self, *args): 
    print "Entering", self.f.__name__ 
    r = self.f(*args) 
    print "Exited", self.f.__name__ 
    return r
print 'decorator using'
@entryExit 
def hello(a): 
print 'inside hello' 
return "hello world " + a
print 'test start' 
print hello('friends')
>>> ================================ RESTART ================================ 
>>> 
decorator using 
entry init enter 
entry init exit 
test start 
Entering hello 
inside hello 
Exited hello 
hello world friends