子类化 Python 的 `property` [英] Subclassing Python's `property`

问题描述

在我的一个类中，我有许多属性在获取和设置方面做非常相似的事情.所以我将 property 的参数抽象成一个工厂函数:

In one of my classes, I have a number of properties that do very similar things on getting and setting. So I abstracted the arguments to property into a factory function:

def property_args(name):
    def getter(self):
        # do something
        return getattr(self, '_' + name)
    def setter(self, value)
        # do something
        setattr(self, '_' + name, value)
    return getter, setter

class MyClass(object):
    def __init__(self):
        self._x = None
    x = property(*property_args('x'))  # obviously there's more than one of these IRL

然而，我后来发现 property 实际上是一个类，将它子类化将是完美的选择.我在文档中找不到任何解释我需要覆盖的内容(以及 __init__ 等的参数签名)，而且我真的不想去寻找 C 源代码为了它.有谁知道我在哪里可以找到这些信息?

However, I've since discovered that property is in fact a class, and subclassing it would be perfect for this. I can't find anything in the documentation that explains what I need to override (and the argument signatures of __init__ etc), and I don't really want to have to go hunting in the C source code for it. Does anyone know where I can find this information?

推荐答案

以下是 property() 中代码的纯 Python 等效项:

Here is a pure Python equivalent for the code in property():

class Property(object):
    "Emulate PyProperty_Type() in Objects/descrobject.c"

    def __init__(self, fget=None, fset=None, fdel=None, doc=None):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel
        if doc is None and fget is not None:
            doc = fget.__doc__
        self.__doc__ = doc

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        if self.fget is None:
            raise AttributeError("unreadable attribute")
        return self.fget(obj)

    def __set__(self, obj, value):
        if self.fset is None:
            raise AttributeError("can't set attribute")
        self.fset(obj, value)

    def __delete__(self, obj):
        if self.fdel is None:
            raise AttributeError("can't delete attribute")
        self.fdel(obj)

    def getter(self, fget):
        return type(self)(fget, self.fset, self.fdel, self.__doc__)

    def setter(self, fset):
        return type(self)(self.fget, fset, self.fdel, self.__doc__)

    def deleter(self, fdel):
        return type(self)(self.fget, self.fset, fdel, self.__doc__)

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