Python装饰器,分两部分,一是装饰器本身的定义,一是被装饰器对象的定义。
一、函数式装饰器:装饰器本身是一个函数。
1.装饰函数:被装饰对象是一个函数
[1]装饰器无参数:
a.被装饰对象无参数:
>>> def test(func): def _test(): print 'Call the function %s().'%func.func_name return func() return _test>>> @test def say():return 'hello world'
>>> say() Call the function say(). 'hello world' >>>
b.被装饰对象有参数:
>>> def test(func): def _test(*args,**kw): print 'Call the function %s().'%func.func_name return func(*args,**kw) return _test>>> @test def left(Str,Len): #The parameters of _test can be '(Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) Call the function left(). 'hello' >>>
[2]装饰器有参数:
a.被装饰对象无参数:
>>> def test(printResult=False): def _test(func): def __test(): print 'Call the function %s().'%func.func_name if printResult: print func() else: return func() return __test return _test>>> @test(True) def say():return 'hello world'
>>> say() Call the function say(). hello world >>> @test(False) def say():return 'hello world'
>>> say() Call the function say(). 'hello world' >>> @test() def say():return 'hello world'
>>> say() Call the function say(). 'hello world' >>> @test def say():return 'hello world'
>>> say()
Traceback (most recent call last): File "<pyshell#224>", line 1, in <module> say() TypeError: _test() takes exactly 1 argument (0 given) >>>
b.被装饰对象有参数:
>>> def test(printResult=False): def _test(func): def __test(*args,**kw): print 'Call the function %s().'%func.func_name if printResult: print func(*args,**kw) else: return func(*args,**kw) return __test return _test>>> @test() def left(Str,Len): #The parameters of __test can be '(Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) Call the function left(). 'hello' >>> @test(True) def left(Str,Len): #The parameters of __test can be '(Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) Call the function left(). hello >>>
[1]装饰器无参数:
a.被装饰对象无参数:
>>> def test(cls): def _test(): clsName=re.findall('(\w+)',repr(cls))[-1] print 'Call %s.__init().'%clsName return cls() return _test>>> @test class sy(object): value=32
>>> s=sy() Call sy.__init(). >>> s <__main__.sy object at 0x0000000002C3E390> >>> s.value 32 >>>
>>> def test(cls): def _test(*args,**kw): clsName=re.findall('(\w+)',repr(cls))[-1] print 'Call %s.__init().'%clsName return cls(*args,**kw) return _test>>> @test class sy(object): def __init__(self,value): #The parameters of _test can be '(value)' in this case. self.value=value
>>> s=sy('hello world') Call sy.__init(). >>> s <__main__.sy object at 0x0000000003AF7748> >>> s.value 'hello world' >>>
a.被装饰对象无参数:
>>> def test(printValue=True): def _test(cls): def __test(): clsName=re.findall('(\w+)',repr(cls))[-1] print 'Call %s.__init().'%clsName obj=cls() if printValue: print 'value = %r'%obj.value return obj return __test return _test>>> @test() class sy(object): def __init__(self): self.value=32
>>> s=sy() Call sy.__init(). value = 32 >>> @test(False) class sy(object): def __init__(self): self.value=32
>>> s=sy() Call sy.__init(). >>>
b.被装饰对象有参数:
>>> def test(printValue=True): def _test(cls): def __test(*args,**kw): clsName=re.findall('(\w+)',repr(cls))[-1] print 'Call %s.__init().'%clsName obj=cls(*args,**kw) if printValue: print 'value = %r'%obj.value return obj return __test return _test>>> @test() class sy(object): def __init__(self,value): self.value=value
>>> s=sy('hello world') Call sy.__init(). value = 'hello world' >>> @test(False) class sy(object): def __init__(self,value): self.value=value
>>> s=sy('hello world') Call sy.__init(). >>>
二、类式装饰器:装饰器本身是一个类,借用__init__()和__call__()来实现职能
1.装饰函数:被装饰对象是一个函数
[1]装饰器无参数:
a.被装饰对象无参数:
>>> class test(object): def __init__(self,func): self._func=func def __call__(self): return self._func()>>> @test def say(): return 'hello world'
>>> say() 'hello world' >>>
b.被装饰对象有参数:
>>> class test(object): def __init__(self,func): self._func=func def __call__(self,*args,**kw): return self._func(*args,**kw)>>> @test def left(Str,Len): #The parameters of __call__ can be '(self,Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) 'hello' >>>
[2]装饰器有参数
a.被装饰对象无参数:
>>> class test(object): def __init__(self,beforeinfo='Call function'): self.beforeInfo=beforeinfo def __call__(self,func): def _call(): print self.beforeInfo return func() return _call>>> @test() def say(): return 'hello world'
>>> say() Call function 'hello world' >>>
或者:
>>> class test(object): def __init__(self,beforeinfo='Call function'): self.beforeInfo=beforeinfo def __call__(self,func): self._func=func return self._call def _call(self): print self.beforeInfo return self._func()>>> @test() def say(): return 'hello world'
>>> say() Call function 'hello world' >>>
b.被装饰对象有参数:
>>> class test(object): def __init__(self,beforeinfo='Call function'): self.beforeInfo=beforeinfo def __call__(self,func): def _call(*args,**kw): print self.beforeInfo return func(*args,**kw) return _call>>> @test() def left(Str,Len): #The parameters of _call can be '(Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) Call function 'hello' >>>
或者:
>>> class test(object): def __init__(self,beforeinfo='Call function'): self.beforeInfo=beforeinfo def __call__(self,func): self._func=func return self._call def _call(self,*args,**kw): print self.beforeInfo return self._func(*args,**kw)>>> @test() def left(Str,Len): #The parameters of _call can be '(self,Str,Len)' in this case. return Str[:Len]
>>> left('hello world',5) Call function 'hello' >>>
[1]装饰器无参数:
a.被装饰对象无参数:
>>> class test(object): def __init__(self,cls): self._cls=cls def __call__(self): return self._cls()>>> @test class sy(object): def __init__(self): self.value=32
>>> s=sy() >>> s <__main__.sy object at 0x0000000003AAFA20> >>> s.value 32 >>>
b.被装饰对象有参数:
>>> class test(object): def __init__(self,cls): self._cls=cls def __call__(self,*args,**kw): return self._cls(*args,**kw)>>> @test class sy(object): def __init__(self,value): #The parameters of __call__ can be '(self,value)' in this case. self.value=value
>>> s=sy('hello world') >>> s <__main__.sy object at 0x0000000003AAFA20> >>> s.value 'hello world' >>>
[2]装饰器有参数:
a.被装饰对象无参数:
>>> class test(object): def __init__(self,printValue=False): self._printValue=printValue def __call__(self,cls): def _call(): obj=cls() if self._printValue: print 'value = %r'%obj.value return obj return _call>>> @test(True) class sy(object): def __init__(self): self.value=32
>>> s=sy() value = 32 >>> s <__main__.sy object at 0x0000000003AB50B8> >>> s.value 32 >>>
b.被装饰对象有参数:
>>> class test(object): def __init__(self,printValue=False): self._printValue=printValue def __call__(self,cls): def _call(*args,**kw): obj=cls(*args,**kw) if self._printValue: print 'value = %r'%obj.value return obj return _call>>> @test(True) class sy(object): def __init__(self,value): #The parameters of _call can be '(value)' in this case. self.value=value
>>> s=sy('hello world') value = 'hello world' >>> s <__main__.sy object at 0x0000000003AB5588> >>> s.value 'hello world' >>>
总结:【1】@decorator后面不带括号时(也即装饰器无参数时),效果就相当于先定义func或cls,而后执行赋值操作func=decorator(func)或cls=decorator(cls);
【2】@decorator后面带括号时(也即装饰器有参数时),效果就相当于先定义func或cls,而后执行赋值操作 func=decorator(decoratorArgs)(func)或cls=decorator(decoratorArgs)(cls);
【3】如上将func或cls重新赋值后,此时的func或cls也不再是原来定义时的func或cls,而是一个可执行体,你只需要传入参数就可调用,func(args)=>返回值或者输出,cls(args)=>object of cls;
【4】最后通过赋值返回的执行体是多样的,可以是闭包,也可以是外部函数;当被装饰的是一个类时,还可以是类内部方法,函数;
【5】另外要想真正了解装饰器,一定要了解func.func_code.co_varnames,func.func_defaults,通过它们你可以以func的定义之外,还原func的参数列表;另外关键字参数是因为调用而出现的,而不是因为func的定义,func的定义中的用等号连接的只是有默认值的参数,它们并不一定会成为关键字参数,因为你仍然可以按照位置来传递它们。