`weakref`回调可以代替`__del__`吗？ [英] Can `weakref` callbacks replace `__del__`?

问题描述

有什么障碍阻止 weakref __ del __ 做的所有事情都做得很好，例如 finalize 这个调用会在解释器退出之前进行，调用的顺序是明确的，等等）？

看起来在遥远的过去有人认为 weakref 最终会导致从语言中删除 __ del __ 。

是什么阻止了这种情况发生？

似乎有一些少数用例 __ del __ ，并且我知道所有的工作似乎至少工作（通常好得多）， weakref 回调或<$ c $

更新： https://www.python.org/dev/peps/pep-0442/ =nofollow noreferrer> PEP 442 显着改善了 __ del __ ，以及@ gz和@ user2357112提到的 weakref 的问题，我想知道该语言是否正在朝着制作 __ del __ 更可靠，或者使用 weakref 而不是 __ del __ ，或者两者兼而有之。

解决方案

有一些实际的原因 __ del __ 仍然存在。一些重要的 weakref 改进，包括 finalize ，都是 python 3.4中的新增功能。所以，用更好的weakrefs替换 __ del __ 就不会出现py3k语言中断变化的窗口。

我认为大多数用途 can 可以被基本的weakref功能取代，但是我对Richard Oudkerk的这个观察结果感到惊讶 issue 15528 在哪里提出并实施定稿：
$ b

当它是一个选项时，使用 __ del__ 方法远不那么麻烦。

无论如何，也许应该在Python 4正在考虑？ ;）

Is there any obstacle that prevents weakref from doing everything that __del__ does but with much stronger guarantees (e.g., finalize guarantees that the call will be made before the interpreter exits, and the order of calls is well-defined, etc.)?

It seems that in the distant past it was thought that weakref would eventually lead to the removal of __del__ from the language.

What prevented this from happening?

There seems to be few use cases for __del__, and all the ones I'm aware of seem to work at least as well (and usually much better) with weakref callbacks or weakref.finalize.

Update:

With PEP 442 dramatically improving the behavior of __del__, and the concerns with weakref mentioned by @gz and @user2357112, I'm wondering if the language is generally moving towards making __del__ more reliable, or towards using weakref instead of __del__, or both.

解决方案

There's a somewhat pragmatic reason __del__ is still around. Several signficant weakref improvements, including finalize, were new in Python 3.4. So, replacing __del__ with better weakrefs missed the window for language breaking changes with py3k.

I think most uses can be replaced by the base weakref functionality, but I'm struck by this observation from Richard Oudkerk in issue 15528 where proposed and implemented finalize:

[Weakref callbacks] are low level, and working out how to use them correctly requires a bit of head scratching. One must find somewhere to store the weakref till after the referent is dead, and without accidentally keeping the referent alive. Then one must ensure that the callback frees the weakref (without leaving any remnant ref-cycles).

When it is an option, using a __del__ method is far less hassle.

Anyway, perhaps the question should be brought up again when Python 4 is being considered? ;)

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