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。