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如何在python抽象类中创建抽象属性

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问题：如何在python抽象类中创建抽象属性
回答 0
回答 1
回答 2

问题：如何在python抽象类中创建抽象属性

在以下代码中，我创建了一个基本抽象类Base。我希望所有从其继承的类都Base提供该name属性，因此我将该属性设置为@abstractmethod。

然后，我创建了一个Base名为的子类，该子类Base_1旨在提供一些功能，但仍保持抽象。中没有name属性Base_1，但是python实例化了该类的对象而没有错误。一个人如何创建抽象属性？

from abc import ABCMeta, abstractmethod
class Base(object):
    __metaclass__ = ABCMeta
    def __init__(self, strDirConfig):
        self.strDirConfig = strDirConfig

    @abstractmethod
    def _doStuff(self, signals):
        pass

    @property    
    @abstractmethod
    def name(self):
        #this property will be supplied by the inheriting classes
        #individually
        pass


class Base_1(Base):
    __metaclass__ = ABCMeta
    # this class does not provide the name property, should raise an error
    def __init__(self, strDirConfig):
        super(Base_1, self).__init__(strDirConfig)

    def _doStuff(self, signals):
        print 'Base_1 does stuff'


class C(Base_1):
    @property
    def name(self):
        return 'class C'


if __name__ == '__main__':
    b1 = Base_1('abc')
点击查看英文原文

In the following code, I create a base abstract class Base. I want all the classes that inherit from Base to provide the name property, so I made this property an @abstractmethod.

Then I created a subclass of Base, called Base_1, which is meant to supply some functionality, but still remain abstract. There is no name property in Base_1, but nevertheless python instatinates an object of that class without an error. How does one create abstract properties?

from abc import ABCMeta, abstractmethod
class Base(object):
    __metaclass__ = ABCMeta
    def __init__(self, strDirConfig):
        self.strDirConfig = strDirConfig

    @abstractmethod
    def _doStuff(self, signals):
        pass

    @property    
    @abstractmethod
    def name(self):
        #this property will be supplied by the inheriting classes
        #individually
        pass


class Base_1(Base):
    __metaclass__ = ABCMeta
    # this class does not provide the name property, should raise an error
    def __init__(self, strDirConfig):
        super(Base_1, self).__init__(strDirConfig)

    def _doStuff(self, signals):
        print 'Base_1 does stuff'


class C(Base_1):
    @property
    def name(self):
        return 'class C'


if __name__ == '__main__':
    b1 = Base_1('abc')

回答 0

从Python 3.3开始，修复了一个错误，这意味着property()装饰器现在应用于抽象方法时，可以正确地标识为抽象。

注：订单的问题，你必须使用@property前@abstractmethod

Python 3.3以上版本：（python docs）：

class C(ABC):
    @property
    @abstractmethod
    def my_abstract_property(self):
        ...

Python 2：（python docs）

class C(ABC):
    @abstractproperty
    def my_abstract_property(self):
        ...
点击查看英文原文

Since Python 3.3 a bug was fixed meaning the property() decorator is now correctly identified as abstract when applied to an abstract method.

Note: Order matters, you have to use @property before @abstractmethod

Python 3.3+: (python docs):

class C(ABC):
    @property
    @abstractmethod
    def my_abstract_property(self):
        ...

Python 2: (python docs)

class C(ABC):
    @abstractproperty
    def my_abstract_property(self):
        ...

回答 1

在Python 3.3之前，您不能嵌套@abstractmethod和@property。

使用@abstractproperty创建抽象属性（文档）。

from abc import ABCMeta, abstractmethod, abstractproperty

class Base(object):
    # ...
    @abstractproperty
    def name(self):
        pass

该代码现在引发正确的异常：

追溯（最近一次通话）：
  在第36行的文件“ foo.py”中 
    b1 = Base_1（'abc'）  
TypeError：无法使用抽象方法名称实例化抽象类Base_1
点击查看英文原文

Until Python 3.3, you cannot nest @abstractmethod and @property.

Use @abstractproperty to create abstract properties (docs).

from abc import ABCMeta, abstractmethod, abstractproperty

class Base(object):
    # ...
    @abstractproperty
    def name(self):
        pass

The code now raises the correct exception:

Traceback (most recent call last):
  File "foo.py", line 36, in 
    b1 = Base_1('abc')  
TypeError: Can't instantiate abstract class Base_1 with abstract methods name

回答 2

根据上面的詹姆斯回答 

def compatibleabstractproperty(func):

    if sys.version_info > (3, 3):             
        return property(abstractmethod(func))
    else:
        return abstractproperty(func)

并将其用作装饰器

@compatibleabstractproperty
def env(self):
    raise NotImplementedError()
点击查看英文原文

Based on James answer above 

def compatibleabstractproperty(func):

    if sys.version_info > (3, 3):             
        return property(abstractmethod(func))
    else:
        return abstractproperty(func)

and use it as a decorator

@compatibleabstractproperty
def env(self):
    raise NotImplementedError()