自定义类型的对象作为字典键 [英] Object of custom type as dictionary key

问题描述

使用自定义类型的对象作为Python字典中的键（我不希望对象id作为键），我该怎么办？

  class MyThing：
 def __init __（self，name，location，length）：
 self.name = name 
 self.location = location 
 self.length = length 
  

I '要使用MyThing作为键，如果名称和位置相同，则认为相同。
从C＃/ Java我习惯于重写并提供一个equals和hashcode方法，并且承诺不突变哈希码依赖的任何东西。

在Python中我该怎么做才能完成这个？我应该呢

（在一个简单的情况下，像这里，或许最好只是放置一个（名称，位置）元组作为关键 - 但是考虑我想要关键成为一个对象）

解决方案

您需要添加 2方法，注意 __哈希__ 和 __ eq __

  class MyThing：
 def __init __（self，name，location，length）：
 self.name = name 
 self.location = location 
 self.length = length 
 
 def __hash __（self）：
 return hash（（self.name ，self.location））
 
 def __eq __（self，other）：
 return（self.name，self.location）==（other.name，other.location）
 
 def __ne __（self，other）：
＃不是绝对必要的，但是要避免同时使用x == y和x！= y 
＃True同时
 return not（self == other）
  

Python dict documentation 定义了关键对象的这些要求，即它们必须是 hashable 。

What must I do to use my objects of a custom type as keys in a Python dictionary (where I don't want the "object id" to act as the key) , e.g.

class MyThing:
    def __init__(self,name,location,length):
            self.name = name
            self.location = location
            self.length = length

I'd want to use MyThing's as keys that are considered the same if name and location are the same. From C#/Java I'm used to having to override and provide an equals and hashcode method, and promise not to mutate anything the hashcode depends on.

What must I do in Python to accomplish this ? Should I even ?

(In a simple case, like here, perhaps it'd be better to just place a (name,location) tuple as key - but consider I'd want the key to be an object)

解决方案

You need to add 2 methods, note __hash__ and __eq__:

class MyThing:
    def __init__(self,name,location,length):
        self.name = name
        self.location = location
        self.length = length

    def __hash__(self):
        return hash((self.name, self.location))

    def __eq__(self, other):
        return (self.name, self.location) == (other.name, other.location)

    def __ne__(self, other):
        # Not strictly necessary, but to avoid having both x==y and x!=y
        # True at the same time
        return not(self == other)

The Python dict documentation defines these requirements on key objects, i.e. they must be hashable.

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