Question

我正在尝试用另一个类来装饰一个类。我也想继承装饰类，但是我遇到了一些错误。这是我的代码：

class Decorator:
    def __init__(self, decorated):
        pass

@Decorator
class Foo:
    pass

class Goo(Foo):
    pass

我尝试从Foo进行子类化时得到的错误是：

追踪（最近的呼叫最后）：
  文件“test.py”，第9行，在   Goo（Foo）：
  TypeError：__ init __（）只需要2个位置参数（给定4个）

将另一个init函数添加到Decorator ...

def __init__(self, *args):
    for arg in args:
        print(arg)

...我得到以下输出：

＆lt; class'__main __。Foo'＆gt;
  GOO
  （＆lt; __ main __。修饰器对象位于0x010073B0＆gt;，）
  {'__ module _'：'_ _ main __'}

这些参数是什么？如何在Decorator内使用它们？

Answer 1

我会尝试回答“这些参数是什么”的问题。这段代码：

@Decorator
class Foo:
    pass

相当于：

class Foo:
    pass
Foo = Decorator(Foo)

这意味着Foo最终成为Decorator类的实例而不是类。

当您尝试将此实例用作类（Goo）的基础时，Python必须确定将用于创建新类的元类。在这种情况下，它将使用等于Foo.__class__的{{1}}。然后它将使用Decorator参数调用元类，并期望它返回一个新类。

这就是你在(name, bases, dict)中结束这些论点的方式。

有关此内容的更多信息，请访问： http://www.python.org/download/releases/2.2.3/descrintro/#metaclasses （特别是“当执行类声明时......”部分）

Answer 2

在定义类之后，您是否尝试将MixIn添加到类中？如果是这样，你可以这样注入MixIn：

def inject_class(mixin):
    def _inject_class(cls):
        return type(cls.__name__,(mixin,)+cls.__bases__,dict(cls.__dict__))
    return _inject_class

class MixIn(object):
    def mix(self):
        print('mix')

@inject_class(MixIn)
class Foo(object):
    def foo(self):
        print('foo')

class Goo(Foo):
    def goo(self):
        print('goo')

goo=Goo()
goo.mix()
goo.foo()
goo.goo()

打印

mix
foo
goo

如果你不想要inject_class的一般性，你可以制作一个专门的类装饰器，它只混合在Decorator中：

def decorate(cls):
    class Decorator(object):
        def deco(self):
            print('deco')
    return type(cls.__name__,(Decorator,)+cls.__bases__,dict(cls.__dict__))

@decorate
class Foo(object):
    def foo(self):
    print('foo')

结果是一样的。

Answer 3

我遇到了同样的问题，以下解决方案对我有用：

from functools import update_wrapper
class decoratorBase():
    def __new__(cls, logic):
        self = object.__new__(cls)
        self.__init__(logic)
        def new (cls):
            #cls is the decorated class type, not the decorator class type itself
            self._createInstance(cls)
            self._postInstanceCreation()
            return self
        self._logic.__new__ = new
        #return the wrapped class and not a wrapper
        return self._logic
    def __init__(self, logic):
        #logic is the decorated class
        self._logic = logic
    def _createInstance(self, cls):
        self._logicInstance = object.__new__(cls)
        self._logicInstance.__init__()
    def _postInstanceCreation(self):
        pass

class factory(decoratorBase):
    def __init__(self, *largs, **kwargs):
        super().__init__(*largs, **kwargs)
        self.__instance = None
    def _createInstance(self, cls):
        self._logicInstance = None
        self._cls = cls
    def _postInstanceCreation(self):
        update_wrapper(self, self._cls)
    def __call__(self, userData, *largs, **kwargs):
        logicInstance = object.__new__(self._cls)
        logicInstance.__init__(*largs, **kwargs)
        logicInstance._update(userData)
        return logicInstance

class singelton(decoratorBase):
    def _postInstanceCreation(self):
        update_wrapper(self, self._logicInstance)
    def __call__(self, userData):
        self._logicInstance._update(userData)
        return self._logicInstance

class base():
    def __init__(self):
        self.var = 0
        print ("Create new object")
    def __call__(self):
        self.var += self._updateValue()
    def _update(self, userData):
        print ("Update object static value with {0}".format(userData))
        self.var = userData

@factory
class factoryTestBase(base):

    def __call__(self):
        super().__call__()
        print("I'm a factory, here is the proof: {0}".format(self.var))
    def _updateValue(self):
        return 1

class factoryTestDerived(factoryTestBase):
    def _updateValue(self):
        return 5

@singelton
class singeltonTestBase(base):
    def __call__(self):
        super().__call__()
        print("I'm a singelton, here is the proof: {0}".format(self.var))
    def _updateValue(self):
        return 1

class singeltonTestDerived(singeltonTestBase):
    def _updateValue(self):
        return 5

这种方法的神奇之处在于__new__()方法的重载，以及装饰器本身的重载以及装饰器返回的“包装器”。我在引号中设置了单词包装器，因为实际上没有包装器。相反，装饰类由装饰器交替并返回。使用此方案，您可以从装饰类继承。最重要的是更改了装饰类的__new__()方法，该方法由以下几行组成：

        def new (cls):
            self._createInstance(cls)
            self._postInstanceCreation()
            return self
        self._logic.__new__ = new

使用此方法，您可以在从装饰类创建对象期间访问装饰器方法，如self._createInstance()。您甚至有机会从装饰器继承（如示例中所示）。

现在让我们举一个简单的例子：

>>> factoryObjCreater = factoryTestBase()
>>> factoryObj1 = factoryObjCreater(userData = 1)
Create new object
Update object static value with 1
>>> factoryObj2 = factoryObjCreater(userData = 1)
Create new object
Update object static value with 1
>>> factoryObj1()
I'm a factory, here is the proof: 2
>>> factoryObj2()
I'm a factory, here is the proof: 2
>>> factoryObjDerivedCreater = factoryTestDerived()
>>> factoryObjDerived1 = factoryObjDerivedCreater(userData = 2)
Create new object
Update object static value with 2
>>> factoryObjDerived2 = factoryObjDerivedCreater(userData = 2)
Create new object
Update object static value with 2
>>> factoryObjDerived1()
I'm a factory, here is the proof: 7
>>> factoryObjDerived2()
I'm a factory, here is the proof: 7
>>> singeltonObjCreater = singeltonTestBase()
Create new object
>>> singeltonObj1 = singeltonObjCreater(userData = 1)
Update object static value with 1
>>> singeltonObj2 = singeltonObjCreater(userData = 1)
Update object static value with 1
>>> singeltonObj1()
I'm a singelton, here is the proof: 2
>>> singeltonObj2()
I'm a singelton, here is the proof: 3
>>> singeltonObjDerivedCreater = singeltonTestDerived()
Create new object
>>> singeltonObjDerived1 = singeltonObjDerivedCreater(userData = 2)
Update object static value with 2
>>> singeltonObjDerived2 = singeltonObjDerivedCreater(userData = 2)
Update object static value with 2
>>> singeltonObjDerived1()
I'm a singelton, here is the proof: 7
>>> singeltonObjDerived2()
I'm a singelton, here is the proof: 12
>>>

继承自装饰类

3 个答案: