有什么办法在Python中创建类属性吗？ [英] Is there any way to create a class property in Python?

问题描述

以下因某种原因无法使用：

The following doesn't work for some reason:

>>> class foo(object):
...     @property
...     @classmethod
...     def bar(cls):
...             return "asdf"
... 
>>> foo.bar
<property object at 0x1da8d0>
>>> foo.bar + '\n'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'property' and 'str'

推荐答案

如果你有一种方法可以做到这一点，想让描述符属性在从对象X获取属性时触发，然后必须将描述符放在 type（X）。所以如果X是一个类，描述符必须放在类的类型中，也就是类的元类 - 不涉及欺骗，它只是一个完全一般的规则。

If you want the descriptor property to trigger when you get an attribute from object X, then you must put the descriptor in type(X). So if X is a class, the descriptor must go in the class's type, also known as the class's metaclass -- no "trickery" involved, it's just a matter of completely general rules.

或者，您可以编写自己的特殊用途描述符。请参见此处了解关于描述符的出色的操作方法条约。 编辑例如：

Alternatively, you might write your own special-purpose descriptor. See here for an excellent "how-to" treaty on descriptors. Edit for example:

class classprop(object):
  def __init__(self, f):
    self.f = classmethod(f)
  def __get__(self, *a):
    return self.f.__get__(*a)()

class buh(object):
  @classprop
  def bah(cls): return 23

print buh.bah

根据需要发出 23 。

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