问题描述
在其他语言(例如Java)中，对象引用可以是强"，弱"，软"或幻影"( http://weblogs.java.net/blog/enicholas/archive/2006/05/understanding_w.html ).
In other languages (e.g. Java), object references can be Strong, Weak, Soft or Phantom (http://weblogs.java.net/blog/enicholas/archive/2006/05/understanding_w.html).
在Python中，默认情况下引用是强"引用，而WeakRef模块则允许使用弱引用.
In Python, references are Strong by default and the WeakRef module allows weak references.
在Python中是否可以使用软引用"?
Is it possible to have "soft references" in Python?
在我的特殊情况下，我有一个创建对象的缓存，这些对象很耗时.有时可能没有对缓存对象的引用，但是如果不需要(即如果有足够的内存)，我不想扔掉缓存的对象.
In my particular case, I have a cache of objects that are time-consuming to create. Sometimes there may be no references to a cached object, but I don't want to throw the cached object away if I don't have to (i.e. if memory is plentiful).
推荐答案
除了硬(又称强")&虚弱的.
Python doesn't natively offer any flavors of references besides hard (aka strong) & weak.
也就是说，此处是我大约一年前提出的softref实现.在一些需要使用的地方使用.它提供的不是真正的软引用，但是对于大多数用例来说，它是很接近的.边缘有些粗糙，但是功能齐全……尽管它依赖于内部的一些引用计数，这意味着它可能会破坏除CPython之外的任何东西.
That said, here is a softref implementation I whipped up a year or so ago which I've been using in a few places I needed one. What it provides aren't quite actual soft references, but it comes close for most use cases. It's a little rough around the edges, but is fully functional... though it relies on some reference counting internally that means it'll probably break on anything except CPython.
特别是，我专门为缓存创建昂贵的长寿命对象而编写了它……SoftValueDictionary应该正是您要寻找的东西.
In particular, I wrote it precisely for a cache of expensive-to-create long-lived objects... the SoftValueDictionary should be exactly what you're looking for.
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