散列（无）如何计算？ [英] How is hash(None) calculated?

问题描述

在我的机器上， hash（None）返回一个值：

 >>>散列（无）
 -2138947203 
  

出于好奇，这个散列值是如何计算的？它看起来好像不是基于 None 的 id ，因为如果我重新启动Python解释器。

解决方案 基于None的 id code>，但None是被定义为C全局变量的少数Python对象之一，所以它的地址（通常）在Python运行之间不会改变。其他这样的对象是 True 和 False （但是它们被散列为整数），或者内置类如 object 和元组。

地址（和散列）是但是，不同的CPython版本不同。在我的系统中， hash（无）给出539708。

On my machine, hash(None) returns a value:

>>> hash(None)
-2138947203

Just out of curiosity, how is this hash value calculated? It doesn't seem as though this value is based on None's id as it is the same if I restart the Python interpreter.

解决方案

It is based on None's id, but None is one of a few Python objects that are defined as C global variables, so its address (typically) doesn't change between Python runs. Other such objects are True and False (but these are hashed as ints), or built-in classes like object and tuple.

The address (and hash) is different between different CPython builds, however. On my system, hash(None) gives 539708.

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