在python中对类实例进行排序 [英] Sorting class instances in python

问题描述

python 2.7用什么对普通类实例进行排序?我对默认的排序行为感兴趣.

What does python 2.7 use to sort vanilla class instances? I'm interested in the default sorting behavior.

假设我有课

class S():
    pass

然后，我可以创建几个实例，并对它们进行排序:

Then I can create a couple of instances, and sort them:

a = S(); b = S(); c = S()
l = [(a,'a'), (b,'b') ,(c, 'c')]
sorted(l)

这将打印一些排序的对象.现在我有一个两部分的问题:

This will print some sorting of the objects. Now I have a two part question:

• python是否使用对象的__hash__()，并因此使用它们的id()?
• 是否可以覆盖__hash__()来影响排序行为?

• Is python using the objects' __hash__(), and thus their id()?
• Is it possible to override __hash__() to influence the sorting behavior?

推荐答案

Python的排序算法专门使用小于"测试比较项目，该测试可以使用__cmp__()特殊方法(现已弃用)或在班上.

Python's sort algorithm exclusively compares items using a "less than" test, which can be implemented either using the __cmp__() special method (now deprecated) or __lt__() on the class.

在没有关于如何比较两个对象的任何特定说明的情况下，与您的情况相同，id()用于同类型的对象(而不是哈希).

In the absence of any specific instruction on how to compare two objects, the id() is used (not the hash) for objects of the same type, as in your case.

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