Python装饰器学习(九步入门) 分类: python学习 2015-03-06 14:26 90人阅读 评论(0) 收藏
原文网址:http://www.cnblogs.com/rhcad/archive/2011/12/21/2295507.html
这是在Python学习小组上介绍的内容,现学现卖、多练习是好的学习方式。
第一步:最简单的函数,准备附加额外功能
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# -*- coding:gbk -*- '''示例1: 最简单的函数,表示调用了两次''' def
myfunc(): print ( "myfunc() called." ) myfunc() myfunc() |
第二步:使用装饰函数在函数执行前和执行后分别附加额外功能
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# -*- coding:gbk -*- '''示例2: 替换函数(装饰) 装饰函数的参数是被装饰的函数对象,返回原函数对象 装饰的实质语句: myfunc = deco(myfunc)''' def
deco(func): print ( "before myfunc() called." ) func() print ( " after myfunc() called." ) return func def
myfunc(): print ( " myfunc() called." ) myfunc = deco(myfunc) myfunc() myfunc() |
第三步:使用语法糖@来装饰函数
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# -*- coding:gbk -*- '''示例3: 使用语法糖@来装饰函数,相当于“myfunc = deco(myfunc)” 但发现新函数只在第一次被调用,且原函数多调用了一次''' def
deco(func): print ( "before myfunc() called." ) func() print ( " after myfunc() called." ) return func @deco def
myfunc(): print ( " myfunc() called." ) myfunc() myfunc() |
第四步:使用内嵌包装函数来确保每次新函数都被调用
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# -*- coding:gbk -*- '''示例4: 使用内嵌包装函数来确保每次新函数都被调用, 内嵌包装函数的形参和返回值与原函数相同,装饰函数返回内嵌包装函数对象''' def
deco(func): def _deco(): print ( "before myfunc() called." ) func() print ( " after myfunc() called." ) # 不需要返回func,实际上应返回原函数的返回值 return _deco @deco def
myfunc(): print ( " myfunc() called." ) return 'ok' myfunc() myfunc() |
第五步:对带参数的函数进行装饰
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# -*- coding:gbk -*- '''示例5: 对带参数的函数进行装饰, 内嵌包装函数的形参和返回值与原函数相同,装饰函数返回内嵌包装函数对象''' def
deco(func): def _deco(a, b): print ( "before myfunc() called." ) ret =
func(a, b) print ( " after myfunc() called. result: %s" %
ret) return ret return _deco @deco def
myfunc(a, b): print ( " myfunc(%s,%s) called." %
(a, b)) return a
+ b myfunc( 1 , 2 ) myfunc( 3 , 4 ) |
第六步:对参数数量不确定的函数进行装饰
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# -*- coding:gbk -*- '''示例6: 对参数数量不确定的函数进行装饰, 参数用(*args, **kwargs),自动适应变参和命名参数''' def
deco(func): def _deco( * args, * * kwargs): print ( "before %s called." %
func.__name__) ret =
func( * args, * * kwargs) print ( " after %s called. result: %s" %
(func.__name__, ret)) return ret return _deco @deco def
myfunc(a, b): print ( " myfunc(%s,%s) called." %
(a, b)) return a + b @deco def
myfunc2(a, b, c): print ( " myfunc2(%s,%s,%s) called." %
(a, b, c)) return a + b + c myfunc( 1 , 2 ) myfunc( 3 , 4 ) myfunc2( 1 , 2 ,
3 ) myfunc2( 3 , 4 ,
5 ) |
第七步:让装饰器带参数
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# -*- coding:gbk -*- '''示例7: 在示例4的基础上,让装饰器带参数, 和上一示例相比在外层多了一层包装。 装饰函数名实际上应更有意义些''' def
deco(arg): def _deco(func): def __deco(): print ( "before %s called [%s]." %
(func.__name__, arg)) func() print ( " after %s called [%s]." %
(func.__name__, arg)) return __deco return _deco @deco ( "mymodule" ) def
myfunc(): print ( " myfunc() called." ) @deco ( "module2" ) def
myfunc2(): print ( " myfunc2() called." ) myfunc() myfunc2() |
第八步:让装饰器带 类 参数
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# -*- coding:gbk -*- '''示例8: 装饰器带类参数''' class
locker: def __init__( self ): print ( "locker.__init__() should be not called." ) @staticmethod def acquire(): print ( "locker.acquire() called.(这是静态方法)" ) @staticmethod def release(): print ( " locker.release() called.(不需要对象实例)" ) def
deco( cls ): '''cls 必须实现acquire和release静态方法''' def _deco(func): def __deco(): print ( "before %s called [%s]." %
(func.__name__, cls )) cls .acquire() try : return func() finally : cls .release() return __deco return _deco @deco (locker) def
myfunc(): print ( " myfunc() called." ) myfunc() myfunc() |
第九步:装饰器带类参数,并分拆公共类到其他py文件中,同时演示了对一个函数应用多个装饰器
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# -*- coding:gbk -*- '''mylocker.py: 公共类 for 示例9.py''' class
mylocker: def __init__( self ): print ( "mylocker.__init__() called." ) @staticmethod def acquire(): print ( "mylocker.acquire() called." ) @staticmethod def unlock(): print ( " mylocker.unlock() called." ) class
lockerex(mylocker): @staticmethod def acquire(): print ( "lockerex.acquire() called." ) @staticmethod def unlock(): print ( " lockerex.unlock() called." ) def
lockhelper( cls ): '''cls 必须实现acquire和release静态方法''' def _deco(func): def __deco( * args, * * kwargs): print ( "before %s called." %
func.__name__) cls .acquire() try : return func( * args, * * kwargs) finally : cls .unlock() return __deco return _deco |
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# -*- coding:gbk -*- '''示例9: 装饰器带类参数,并分拆公共类到其他py文件中 同时演示了对一个函数应用多个装饰器''' from
mylocker import * class
example: @lockhelper (mylocker) def myfunc( self ): print ( " myfunc() called." ) @lockhelper (mylocker) @lockhelper (lockerex) def myfunc2( self , a, b): print ( " myfunc2() called." ) return a
+ b if
__name__ = = "__main__" : a =
example() a.myfunc() print (a.myfunc()) print (a.myfunc2( 1 , 2 )) print (a.myfunc2( 3 , 4 )) |
下面是参考资料,当初有不少地方没看明白,真正练习后才明白些:
1. Python装饰器学习 http://blog.csdn.net/thy38/article/details/4471421
2. Python装饰器与面向切面编程 http://www.cnblogs.com/huxi/archive/2011/03/01/1967600.html
3. Python装饰器的理解 http://apps.hi.baidu.com/share/detail/17572338
作者追加评论:
1、对于装饰函数的最里层函数,最好再加上“@functools.wraps(func)”的修饰,这样就能保留原函数的特殊属性,例如:
import functools
def lockhelper(cls):
def _deco(func):
@functools.wraps(func)
def __deco(*args, **kwargs):
2、以上例子都是对每个函数单独进行包装,在待包装函数之前都有一个@,是否可以不在每个函数前都加修饰呢?下面这篇博文的末尾处介绍了一种自动遍历类的每个方法,自动为每个方法添加装饰:
http://blog.csdn.net/zylcf818/article/details/5342276
我对自动批量添加装饰进行了试验,可支持多个装饰器,效果挺好:http://www.cnblogs.com/rhcad/archive/2011/12/21/2296063.html
****************************
后记:看到一个词:语法糖,然后查到python的装饰器。看到本文,通过debug代码,稍微理解了正文中各部方式,不过刚入门
以下是我测试的代码的输出:
一
myfunc() called.
myfunc() called.
二
before myfunc() called.
myfunc() called.
after myfunc() called.
myfunc() called.
myfunc() called.
三
before myfunc() called.
myfunc() called.
after myfunc() called.
myfunc() called.
myfunc() called.
四
before myfunc() called.
myfunc() called.
after myfunc() called.
before myfunc() called.
myfunc() called.
after myfunc() called.
五(多的xxxx是以为我在myfun的返回之前加的一句print 'xxxx')
before myfunc() called.
myfunc(1,2) called.
xxxx
after myfunc() called. result: 3
before myfunc() called.
myfunc(3,4) called.
xxxx
after myfunc() called. result: 7
六(其中deco中的‘return ret’注释掉好像没有影响)
before myfunc called.
myfunc(1,2) called.
after myfunc called. result: 3
before myfunc called.
myfunc(3,4) called.
after myfunc called. result: 7
before myfunc2 called.
myfunc2(1,2,3) called.
after myfunc2 called. result: 6
before myfunc2 called.
myfunc2(3,4,5) called.
after myfunc2 called. result: 12
七
before myfunc called [mymodule].
myfunc() called.
after myfunc called [mymodule].
before myfunc2 called [module2].
myfunc2() called.
after myfunc2 called [module2].
八(没有打印文中的汉字是因为之前中文报错,改成英语的)
before myfunc called [__main__.locker].
locker.acquire() called.(This is static method)
myfunc() called.
locker.release() called.(No need Object instance)
before myfunc called [__main__.locker].
locker.acquire() called.(This is static method)
myfunc() called.
locker.release() called.(No need Object instance)
九(这一步的前半段是写在mylocker.py中的,其中class lockerex(mylocker):改成class lockerex():好像对结果不造成影响。这里应该表示两个类的相互继承的意思吧)
before myfunc called.
mylocker.acquire() called.
myfunc() called.
mylocker.unlock() called.
before myfunc called.
mylocker.acquire() called.
myfunc() called.
mylocker.unlock() called.
None
before __deco called.
mylocker.acquire() called.
before myfunc2 called.
lockerex.acquire() called.
myfunc2() called.
lockerex.unlock() called.
mylocker.unlock() called.
3
before __deco called.
mylocker.acquire() called.
before myfunc2 called.
lockerex.acquire() called.
myfunc2() called.
lockerex.unlock() called.
mylocker.unlock() called.
7
注:这些结果可能与原结果有些不同,因为中间我可能有些小小的改动,懒得去查了。还有代码中有些return是估计无用的。本来一边学一边记可能会加些笔记,现在只能加些结果了。