Python装饰器学习（九步入门）

ython装饰器学习（九步入门）

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

?12345678# -*- coding:gbk -*-'''示例1: 最简单的函数,表示调用了两次'''?defmyfunc():????print("myfunc() called.")?myfunc()myfunc()

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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

?123456789101112131415161718# -*- 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)'''?defdeco(func):????print("before myfunc() called.")????func()????print("? after myfunc() called.")????returnfunc?defmyfunc():????print(" myfunc() called.")?myfunc =deco(myfunc)?myfunc()myfunc()

第三步：使用语法糖@来装饰函数

?12345678910111213141516# -*- 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'''?defdeco(func):????print("before myfunc() called.")????func()????print("? after myfunc() called.")????returnfunc?@decodefmyfunc():????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

?12345678910111213141516171819# -*- 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'''?defdeco(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?@decodefmyfunc():????print(" myfunc() called.")????return'ok'?myfunc()myfunc()

第五步：对带参数的函数进行装饰

?12345678910111213141516171819# -*- 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'''?defdeco(func):????def_deco(a, b):????????print("before myfunc() called.")????????ret =func(a, b)????????print("? after myfunc() called. result: %s"%ret)????????returnret????return_deco?@decodefmyfunc(a, b):????print(" myfunc(%s,%s) called."%(a, b))????returna +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

?1234567891011121314151617181920212223242526# -*- 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'''?defdeco(func):????def_deco(*args, **kwargs):????????print("before %s called."%func.__name__)????????ret =func(*args, **kwargs)????????print("? after %s called. result: %s"%(func.__name__, ret))????????returnret????return_deco?@decodefmyfunc(a, b):????print(" myfunc(%s,%s) called."%(a, b))????returna+b?@decodefmyfunc2(a, b, c):????print(" myfunc2(%s,%s,%s) called."%(a, b, c))????returna+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

?123456789101112131415161718192021222324# -*- 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'''?defdeco(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")defmyfunc():????print(" myfunc() called.")?@deco("module2")defmyfunc2():????print(" myfunc2() called.")?myfunc()myfunc2()

第八步：让装饰器带 类 参数

?12345678910111213141516171819202122232425262728293031323334# -*- coding:gbk -*-'''示例8: 装饰器带类参数'''?classlocker:????def__init__(self):????????print("locker.__init__() should be not called.")?????????????@staticmethod????defacquire():????????print("locker.acquire() called.（这是静态方法）")?????????????@staticmethod????defrelease():????????print("? locker.release() called.（不需要对象实例）")?defdeco(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:????????????????returnfunc()????????????finally:????????????????cls.release()????????return__deco????return_deco?@deco(locker)defmyfunc():????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

?123456789101112131415161718192021222324252627282930313233343536# -*- coding:gbk -*-'''mylocker.py: 公共类 for 示例9.py'''?classmylocker:????def__init__(self):????????print("mylocker.__init__() called.")?????????????@staticmethod????defacquire():????????print("mylocker.acquire() called.")?????????????@staticmethod????defunlock():????????print("? mylocker.unlock() called.")?classlockerex(mylocker):????@staticmethod????defacquire():????????print("lockerex.acquire() called.")?????????????@staticmethod????defunlock():????????print("? lockerex.unlock() called.")?deflockhelper(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:????????????????returnfunc(*args, **kwargs)????????????finally:????????????????cls.unlock()????????return__deco????return_deco?1234567891011121314151617181920212223# -*- 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'''?frommylocker import*?classexample:????@lockhelper(mylocker)????defmyfunc(self):????????print(" myfunc() called.")?????@lockhelper(mylocker)????@lockhelper(lockerex)????defmyfunc2(self, a, b):????????print(" myfunc2() called.")????????returna +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