Python集合（[]）如何检查两个对象是否相等？对象需要定义什么方法来自定义？ [英] How does a Python set([]) check if two objects are equal? What methods does an object need to define to customise this?

问题描述

我需要在Python中创建一个'container'对象或类，它保存我也定义的其他对象的记录。该容器的一个要求是，如果两个对象被认为是相同的，则删除一个（任一个）。我的第一个想法是使用 set（[]）作为包含对象，完成这个要求。

I need to create a 'container' object or class in Python, which keeps a record of other objects which I also define. One requirement of this container is that if two objects are deemed to be identical, one (either one) is removed. My first thought was to use a set([]) as the containing object, to complete this requirement.

但是，集合不会删除两个相同的对象实例之一。我必须定义什么才能创建一个？

However, the set does not remove one of the two identical object instances. What must I define to create one?

这是Python代码。

Here is the Python code.

class Item(object):
  def __init__(self, foo, bar):
    self.foo = foo
    self.bar = bar
  def __repr__(self):
    return "Item(%s, %s)" % (self.foo, self.bar)
  def __eq__(self, other):
    if isinstance(other, Item):
      return ((self.foo == other.foo) and (self.bar == other.bar))
    else:
      return False
  def __ne__(self, other):
    return (not self.__eq__(other))

翻译 b
$ b

Interpreter

>>> set([Item(1,2), Item(1,2)])
set([Item(1, 2), Item(1, 2)])

It is clear that __eq__(), which is called by x == y, is not the method called by the set. What is called? What other method must I define?

注意： Item 必须保持可变，并且可以更改，因此我无法提供 __哈希__（） 方法。如果这是唯一的方法，那么我将重写使用不可变的 Item 。

Note: The Items must remain mutable, and can change, so I cannot provide a __hash__() method. If this is the only way of doing it, then I will rewrite for use of immutable Items.

推荐答案

我恐怕你必须提供一个 __哈希__（）方法。但是你可以用它的方式编码，它不依赖于你的 Item 的可变属性。

I am afraid you will have to provide a __hash__() method. But you can code it the way, that it does not depend on the mutable attributes of your Item.

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