| 标题 | Python中的多重装饰器 |
| 内容 | 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： 代码如下: >>> 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： 代码如下: >>> 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： 代码如下: >>> 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： 代码如下: >>> 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。 代码如下: #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。 |
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