abc.abstractmethod +属性 [英] abc.abstractmethod + property

问题描述

根据 docs ，它应该可以结合使用 @property 和 @ abc.abstractmethod ，因此以下内容应在python3.3中起作用：

According to the docs it should work to combine @property and @abc.abstractmethod so the following should work in python3.3:

import abc

class FooBase(metaclass=abc.ABCMeta):

    @property
    @abc.abstractmethod
    def greet(self):
        """ must be implemented in order to instantiate """
        pass

    @property
    def greet_comparison(self):
        """ must be implemented in order to instantiate """
        return 'hello'

class Foo(FooBase):
    def greet(self):
        return 'hello'

测试实现：

In [6]: foo = Foo()
In [7]: foo.greet
Out[7]: <bound method Foo.greet of <__main__.Foo object at 0x7f935a971f10>>

In [8]: foo.greet()
Out[8]: 'hello'

因此它显然不是属性，因为它应该这样工作：

so it is obviously not a property, because then it should work like that:

In [9]: foo.greet_comparison
Out[9]: 'hello'

也许我'm愚蠢或根本行不通，有人知道吗？

Maybe I'm to stupid or it simply doesn't work, somebody has an idea?

推荐答案

如果要问候成为属性，您仍然需要在实现中使用 @property 装饰器：

If you want greet to be a property, you still need to use the @property decorator in your implementation:

class Foo(FooBase):
    @property
    def greet(self):
        return 'hello'

ABC元类所做的全部工作就是测试您是否在具体类中提供了相同的名称；

All that an ABC metaclass does is test wether or not you have provided the same name in the concrete class; it doesn't care if it is a method or a property or a regular attribute.

因为它不在乎，所以不会神奇地应用属性装饰器。这是一件好的事情；也许在特定的实现中，静态属性足以满足要求，并且属性可能会过大。

Because it doesn't care, it doesn't magically apply property decorators either. This is a good thing; perhaps in a specific implementation a static attribute is enough to satisfy the requirement, and a property would be overkill.

ABC元类的目的是帮助您检测出差距。您的实施；

The purpose of a ABC metaclass is to help you detect gaps in your implementation; it never was intended to enforce the types of the attributes.

请注意，在Python 3.3之前，您不能合并 @property 和 @抽象方法。您必须使用 @abstractproperty 装饰器来代替。在这种情况下，当您的财产需要的不仅仅是简单的吸气剂时，就会存在歧义。 Python 3.3更好地涵盖了这种情况（有关痛苦的细节，请参见问题11610 ）。

Note that before Python 3.3 you can not combine a @property with an @abstractmethod. You would have to use an @abstractproperty decorator instead. There is an ambiguity there when your property needs more than a simple getter in that case; Python 3.3 covers that case much better (see issue 11610 for the painful details).

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