如何在Python中创建只读类属性？ [英] How to create a read-only class property in Python?

问题描述

基本上我想做这样的事情：

Essentially I want to do something like this:

class foo:
    x = 4
    @property
    @classmethod
    def number(cls):
        return x

然后我想要以下工作：

>>> foo.number
4

不幸的是，上述方法不起作用。而不是给我 4 它给我< property object at 0x101786c58> 。有没有办法实现上述？

Unfortunately, the above doesn't work. Instead of given me 4 it gives me <property object at 0x101786c58>. Is there any way to achieve the above?

推荐答案

属性描述符当从类中访问时（即实例在 __ get__中无 方法）。

The property descriptor always returns itself when accessed from a class (ie. when instance is None in its __get__ method).

如果这不是你想要的，你可以写一个新的描述符，总是使用类对象（ owner ）代替实例：

If that's not what you want, you can write a new descriptor that always uses the class object (owner) instead of the instance:

>>> class classproperty(object):
...     def __init__(self, getter):
...         self.getter= getter
...     def __get__(self, instance, owner):
...         return self.getter(owner)
... 
>>> class Foo(object):
...     x= 4
...     @classproperty
...     def number(cls):
...         return cls.x
... 
>>> Foo().number
4
>>> Foo.number
4

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