Python中的多重装饰器

多重装饰器，即多个装饰器修饰同一个对象【实际上并非完全如此，且看下文详解】

1.装饰器无参数：

>>> def first(func):

    print '%s() was post to first()'%func.func_name

    def _first(*args,**kw):

        print 'Call the function %s() in _first().'%func.func_name

        return func(*args,**kw)

    return _first


>>> def second(func):

    print '%s() was post to second()'%func.func_name

    def _second(*args,**kw):

        print 'Call the function %s() in _second().'%func.func_name

        return func(*args,**kw)

    return _second


>>> @first

@second

def test():return 'hello world'
test() was post to second()

_second() was post to first()

>>> test()

Call the function _second() in _first().

Call the function test() in _second().

'hello world'

>>>

实际上它是相当于下面的代码：

>>> def test():

    return 'hello world'
>>> test=second(test)

test() was post to second()

>>> test

<function _second at 0x000000000316D3C8>

>>> test=first(test)

_second() was post to first()

>>> test

<function _first at 0x000000000316D358>

>>> test()

Call the function _second() in _first().

Call the function test() in _second().

'hello world'

>>>

2.装饰器有参数：

>>> def first(printResult=False):

    def _first(func):

        print '%s() was post to _first()'%func.func_name

        def __first(*args,**kw):

            print 'Call the function %s() in __first().'%\

                  func.func_name

            if printResult:

                print func(*args,**kw),'#print in __first().'

            else:

                return func(*args,**kw)

        return __first

    return _first
>>> def second(printResult=False):

    def _second(func):

        print '%s() was post to _second()'%func.func_name

        def __second(*args,**kw):

            print 'Call the function %s() in __second().'%\

                  func.func_name

            if printResult:

                print func(*args,**kw),'#print in __second().'

            else:

                return func(*args,**kw)

        return __second

    return _second
>>> @first(True)

@second(True)

def test():

    return 'hello world'
test() was post to _second()

__second() was post to _first()

>>> test()

Call the function __second() in __first().

Call the function test() in __second().

hello world #print in __second().

None #print in __first().

>>>

如上，第35行输出后调用__second()，而__second()中又调用了test()并print test()，而后返回__first()中继续执行print，而这个print语句print的内容是__second()返回的None

它等同于：

>>> def test():

    return 'hello world'
>>> test=second(True)(test)

test() was post to _second()

>>> 

>>> test

<function __second at 0x000000000316D2E8>

>>> test=first(True)(test)

__second() was post to _first()

>>> test

<function __first at 0x0000000003344C18>

>>>

3.多重装饰器的应用：

比如你是项目经理，你要求每一个代码块都必须有参数检查ArgsType和责任检查ResponsibilityRegister，这样就需要两个装饰器对此代码块进行监督。

#coding=utf-8

import os,sys,re

from collections import OrderedDict
def ArgsType(*argTypes,**kwTypes):

    u'''ArgsType(*argTypes,**kwTypes)

    options=[('opt_UseTypeOfDefaultValue',False)]
    以下为本函数相关的开关，并非类型检验相关的关键字参数，所有options:

    opt_UseTypeOfDefaultValue=>bool:False,为True时，将对没有指定类型的带默

                               认值的参数使用其默认值的类型

    '''

    def _ArgsType(func):

        #确定所有的parameter name

        argNames=func.func_code.co_varnames[:func.func_code.co_argcount]

        #确定所有的default parameter

        defaults=func.func_defaults

        if defaults:

            defaults=dict(zip(argNames[-len(defaults):],defaults))

        else:defaults=None

        #将“参数类型关键字参数”中的所有“options关键字参数”提出

        options=dict()

        for option,default in [('opt_UseTypeOfDefaultValue',False)]:

            options[option]=kwTypes.pop(option,default)

        #argTypes和kwTypes的总长度应该与argNames一致

        if len(argTypes)+len(kwTypes)>len(argNames):

            raise Exception('Too much types to check %s().'%func.func_name)

        #所有kwTypes中的键不能覆盖在argTypes中已经占用的names

        if not set(argNames[len(argTypes):]).issuperset(

            set(kwTypes.keys())):

            raise Exception('There is some key in kwTypes '+

                'which is not in argNames.')

        #确定所有的参数应该有的types

        types=OrderedDict()

        for name in argNames:types[name]=None

        if len(argTypes):

            for i in range(len(argTypes)):

                name=argNames[i]

                types[name]=argTypes[i]

        else:

            for name,t in kwTypes.items():

                types[name]=t

        if len(kwTypes):

            for name,t in kwTypes.items():

                types[name]=t

        #关于default parameter的type

        if options['opt_UseTypeOfDefaultValue']:

            for k,v in defaults.items():

                #如果default parameter的type没有另外指定，那么就使用

                #default parameter的default value的type

                if types[k]==None:

                    types[k]=type(v)

        def __ArgsType(*args,**kw):

            #order the args

            Args=OrderedDict()

            #init keys

            for name in argNames:Args[name]=None

            #init default values

            if defaults is not None:

                for k,v in defaults.items():

                    Args[k]=v

            #fill in all args

            for i in range(len(args)):

                Args[argNames[i]]=args[i]

            #fill in all keyword args

            for k,v in kw.items():

                Args[k]=v

            #check if there is some None in the values

            if defaults==None:

                for k in Args:

                    if Args[k]==None:

                        if defaults==None:

                            raise Exception(('%s() needs %r parameter, '+

                                'which was not given')%(func.func_name,k))

                        else:

                           if not defaults.has_key(k):

                                raise Exception(('Parameter %r of %s() is'+

                                    ' not a default parameter')%\

                                    (k,func.func_name))

            #check all types

            for k in Args:

                if not isinstance(Args[k],types[k]):

                    raise TypeError(('Parameter %r of %s() must be '+

                        'a %r object, but you post: %r')%\

                        (k,func.func_name,types[k],Args[k]))

            return func(*args,**kw)

        return __ArgsType

    return _ArgsType
def ResponsibilityRegister(author):

    def _ResponsibilityRegister(func):

        def __ResponsibilityRegister(*args,**kw):

            try:

                return func(*args,**kw)

            except Exception as e:

                print ("Something is wrong, It's %s's responsibility."%\

                       author).center(80,'*')

                raise e

        return __ResponsibilityRegister

    return _ResponsibilityRegister
@ResponsibilityRegister('Kate')

@ArgsType(str,int)

def left(Str,Len=1):

    return Str[:Len]
print 'Good calling:'

print left('hello world',8)

print 'Bad calling:'

print left(3,7)

这里没有文档，所以调用者不知道，使用了错误的调用，导致出错，这是Kate的责任。

像上面这种，对代码有两种互不相干的检验时，就可以使用多重装饰器。