如何理解Python装饰器?

def inject_check(method):
    def my_method(*args):
        print "before"
        method(*args)
        print "after"
    return my_method
############################    
#class Demo(object):
#    def hello(self):
#        print &q缉恭光枷叱磺癸委含莲uot;hello"
#    hello=inject_check(hello)
##########################
    
class Demo(object):
    @inject_check
    def hello(self):
        print "hello"
        
d = Demo()
d.hello()
就是在函数上加个包装，如上面代码中的hello函数加上@inject_check装饰器，等价于将函数hello重新赋值：hello=inject_check(hello)