了解__getattr__和__getattribute__之间的区别 [英] Understanding the difference between __getattr__ and __getattribute__

问题描述

我试图理解__getattr__和__getattribute__之间的区别，但是，我没有做到这一点.

I am trying to understand the difference between __getattr__ and __getattribute__, however, I am failing at it.

答案堆栈溢出"问题

The answer to the Stack Overflow question Difference between __getattr__ vs __getattribute__ says:

在查看以下内容的实际属性之前，先调用

__getattribute__ 对象，因此可能很难 正确实施.你可以结束于 无限递归非常容易.

__getattribute__ is invoked before looking at the actual attributes on the object, and so can be tricky to implement correctly. You can end up in infinite recursions very easily.

我绝对不知道那是什么意思.

I have absolutely no idea what that means.

然后继续说:

您几乎可以肯定想要__getattr__.

为什么?

我了解到，如果__getattribute__失败，则会调用__getattr__.那么，为什么有两种不同的方法做同样的事情呢?如果我的代码实现了新样式类，我应该使用什么?

I read that if __getattribute__ fails, __getattr__ is called. So why are there two different methods doing the same thing? If my code implements the new style classes, what should I use?

我正在寻找一些代码示例来清除此问题.我已尽我最大的能力来搜索Google，但我发现的答案并未彻底讨论该问题.

I am looking for some code examples to clear this question. I have Googled to best of my ability, but the answers that I found don't discuss the problem thoroughly.

如果有任何文档，我准备阅读.

If there is any documentation, I am ready to read that.

推荐答案

一些基本知识.

对于对象，您需要处理其属性.通常，我们执行instance.attribute.有时我们需要更多的控制权(当我们事先不知道属性名称时).

Some basics first.

With objects, you need to deal with its attributes. Ordinarily we do instance.attribute. Sometimes we need more control (when we do not know the name of the attribute in advance).

例如，instance.attribute将变为getattr(instance, attribute_name).使用此模型，我们可以通过提供 attribute_name 作为字符串来获取属性.

For example, instance.attribute would become getattr(instance, attribute_name). Using this model, we can get the attribute by supplying the attribute_name as a string.

您还可以告诉类如何处理它未显式管理的属性，并通过__getattr__方法来实现.

You can also tell a class how to deal with attributes which it doesn't explicitly manage and do that via __getattr__ method.

每当您请求尚未定义的属性时，Python都会调用此方法，因此您可以定义使用该方法的方法.

Python will call this method whenever you request an attribute that hasn't already been defined, so you can define what to do with it.

一个经典的用例:

class A(dict):
    def __getattr__(self, name):
       return self[name]
a = A()
# Now a.somekey will give a['somekey']

注意事项和__getattribute__

的使用

如果您需要捕获每个属性是否存在 ，请改用__getattribute__.区别在于__getattr__仅针对实际上不存在的属性被调用.如果直接设置属性，则引用该属性将在不调用__getattr__的情况下检索该属性.

Caveats and use of __getattribute__

If you need to catch every attribute regardless whether it exists or not, use __getattribute__ instead. The difference is that __getattr__ only gets called for attributes that don't actually exist. If you set an attribute directly, referencing that attribute will retrieve it without calling __getattr__.

__getattribute__一直被调用.

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