#封装器包含了函数以及其前后执行的代码，其已经准备完毕
return the_wrapper_around_the_original_function
# 现在想象下，你创建了一个你永远也不远再次接触的函数
def a_stand_alone_function() :
print "I am a stand alone function, don't you dare modify me"
a_stand_alone_function()
#输出: I am a stand alone function, don't you dare modify me
# 好了，你可以封装它实现行为的扩展。可以简单的把它丢给装饰器
# 装饰器将动态地把它和你要的代码封装起来，并且返回一个新的可用的函数。
a_stand_alone_function_decorated = my_shiny_new_decorator(a_stand_alone_function)
a_stand_alone_function_decorated()
#输出 :
#Before the function runs
#I am a stand alone function, don't you dare modify me
#After the function runs
现在你也许要求当每次调用a_stand_alone_function时，实际调用却是a_stand_alone_function_decorated。实现也很简单，可以用my_shiny_new_decorator来给a_stand_alone_function重新赋值。
a_stand_alone_function = my_shiny_new_decorator(a_stand_alone_function)
a_stand_alone_function()
#输出 :
#Before the function runs
#I am a stand alone function, don't you dare modify me
#After the function runs
# And guess what, that's EXACTLY what decorators do !
装饰器揭秘
前面的例子，我们可以使用装饰器的语法：
@my_shiny_new_decorator
def another_stand_alone_function() :
print "Leave me alone"
another_stand_alone_function()
#输出 :
#Before the function runs
#Leave me alone
#After the function runs
当然你也可以累积装饰：
def bread(func) :
def wrapper() :
print "</''''''>"
func()
print "<______/>"
return wrapper
def ingredients(func) :
def wrapper() :
print "#tomatoes#"
func()
print "~salad~"
return wrapper
def sandwich(food="--ham--") :
print food
sandwich()
#输出 : --ham--
sandwich = bread(ingredients(sandwich))
sandwich()
#outputs :
#</''''''>
# #tomatoes#
# --ham--
# ~salad~
#<______/>
使用python装饰器语法：
@bread
@ingredients
def sandwich(food="--ham--") :
print food
