python属性获取和设置顺序是什么?

2022-01-13 00:00:00 python class instance-variables attributes metaprogramming

问题描述

Python 为我们提供了很多关于实例/类属性的可能性，例如:

Python provides us many possibilities on instance/class attribute, for example:

class A(object):
    def __init__(self):
        self.foo = "hello"

a = A()

有很多方法可以访问/更改self.foo的值:

There are many ways to access/change the value of self.foo:

  1. 直接访问a.foo
  2. 内部字典 a.__dict__['foo']
  3. 获取和设置a.__get__和a.__set__，当然还有两个预定义的方法.
  4. getattribute a.__getattribute__
  5. __getattr__ 和 __setattr__
  6. 也许更多.
  1. direct access a.foo
  2. inner dict a.__dict__['foo']
  3. get and set a.__get__ and a.__set__,of course there two are pre-defined methods.
  4. getattribute a.__getattribute__
  5. __getattr__ and __setattr__
  6. maybe more.

在阅读源代码时，我总是不知道它们的最终访问顺序是什么?当我使用 a.foo 时，我怎么知道哪个方法/属性会被实际调用?

While reading source code, I always get lost of what's their ultimate access order? When I use a.foo, how do I know which method/attribute will get called actually?

解决方案

bar = a.foo...

  1. 调用 a.__getattribute__('foo')
  2. 默认情况下会查找 a.__dict__['foo']
  3. 如果在 A 上定义，则调用 foo 的 .__get__().
  1. invokes a.__getattribute__('foo')
  2. which in turn by default looks up a.__dict__['foo']
  3. or invokes foo's .__get__() if defined on A.

然后将返回的值分配给 bar.

The returned value would then be assigned to bar.

a.foo = bar...

  1. 调用 a.__getattribute__('foo')
  2. 默认情况下会查找 a.__dict__['foo']
  3. 如果在 A 上定义，则调用 foo 的 .__set__(bar).

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