为什么我不能直接向任何 python 对象添加属性?

问题描述

我有这个代码:

>>> class G:
...   def __init__(self):
...     self.x = 20
...
>>> gg = G()
>>> gg.x
20
>>> gg.y = 2000

还有这段代码:

>>> from datetime import datetime
>>> my_obj = datetime.now()
>>> my_obj.interesting = 1
*** AttributeError: 'datetime.datetime' object has no attribute 'interesting'

根据我的 Python 知识，我会说 datetime 会覆盖 setattr/getattr，但我不确定.你能在这里解释一下吗?

From my Python knowledge, I would say that datetime overrides setattr/getattr, but I am not sure. Could you shed some light here?

我对 datetime 并不特别感兴趣.我想知道一般的对象.

I'm not specifically interested in datetime. I was wondering about objects in general.

---

解决方案

我的猜测，是datetime的实现使用了__slots__ 以获得更好的性能.

My guess, is that the implementation of datetime uses __slots__ for better performance.

当使用 __slots__ 时，解释器只为列出的属性保留存储空间，没有别的.这样可以提供更好的性能并使用更少的存储空间，但这也意味着您不能随意添加新属性.

When using __slots__, the interpreter reserves storage for just the attributes listed, nothing else. This gives better performance and uses less storage, but it also means you can't add new attributes at will.

在此处阅读更多信息:http://docs.python.org/reference/datamodel.html