Python中的各种装饰器详解

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) >>>


由上面这段代码中的最后两个例子可知:当装饰器有参数时,即使你启用装饰器的默认参数,不另外传递新值进去,也必须有一对括号,否则编译器会直接将func传递给test(),而不是传递给_test()

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 >>>


 
2.装饰类:被装饰的对象是一个类

[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 >>>


b.被装饰对象有参数:

>>> 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' >>>


 [2]装饰器有参数:

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' >>>  


  2.装饰类:被装饰对象是一个类

[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。