如何消除等于运算符的python3弃用警告？ [英] How to eliminate a python3 deprecation warning for the equality operator?

问题描述

尽管标题可以解释为三个问题，但实际问题很容易描述。在Linux系统上，我安装了python 2.7.3，并希望收到有关python 3不兼容的警告。因此，我的代码段（ tester.py ）看起来像：

Although the title can be interpreted as three questions, the actual problem is simple to describe. On a Linux system I have python 2.7.3 installed, and want to be warned about python 3 incompatibilities. Therefore, my code snippet (tester.py) looks like:

#!/usr/bin/python -3

class MyClass(object):    
    def __eq__(self, other):
        return False

当我执行此代码段时（只是为了显示问题，而不是我在项目中使用的实际代码）

When I execute this code snippet (thought to be only to show the problem, not an actual piece of code I am using in my project) as

./tester.py

我收到以下弃用警告：

./tester.py:3: DeprecationWarning: Overriding __eq__ blocks inheritance of __hash__ in 3.x
  class MyClass(object):

My问题：如何更改此代码片段以摆脱警告，即使其与版本3兼容？我想以正确的方式实现相等运算符，而不仅仅是抑制警告或类似操作。

My question: How do I change this code snippet to get rid of the warning, i.e. to make it compatible to version 3? I want to implement the equality operator in the correct way, not just suppressing the warning or something similar.

推荐答案

来自文档页面，适用于Python 3.4：

From the documentation page for Python 3.4:

如果类未定义 __ eq __（）方法，它也不应该定义 __ hash __（）操作；如果它定义了 __ eq __（）而不是 __ hash __（），则其实例将不能用作可散列集合中的项目。如果类定义了可变对象并实现了 __ eq __（）方法，则不应实现 __ hash __（），因为可散列集合的实现要求键的散列值是不可变的（如果对象的散列值更改，则它将在错误的散列存储区中）。

If a class does not define an __eq__() method it should not define a __hash__() operation either; if it defines __eq__() but not __hash__(), its instances will not be usable as items in hashable collections. If a class defines mutable objects and implements an __eq__() method, it should not implement __hash__(), since the implementation of hashable collections requires that a key’s hash value is immutable (if the object’s hash value changes, it will be in the wrong hash bucket).

基本上，您需要定义 __ hash（）__ 函数。

Basically, you need to define a __hash()__ function.

问题在于用户定义的类，将自动定义 __ eq（）__ 和 __ hash（）__ 函数。

The problem is that for user-defined classes, the __eq()__ and __hash()__ functions are automatically defined.

x .__ hash __（）返回一个适当的值，使得 x == y 暗示
x是y 和 hash（x）==哈希（y）。

x.__hash__() returns an appropriate value such that x == y implies both that x is y and hash(x) == hash(y).

如果仅定义 __ eq（）__ ，然后将 __ hash（）__ 设置为返回 None 。因此，您会碰壁。

If you define just the __eq()__, then __hash()__ is set to return None. So you will hit the wall.

如果您不想为实现 __ hash（）__ 并且可以肯定地知道对象永远不会被哈希，您只需显式声明 __ hash__ = None 即可处理警告。

The simpler way out if you don't want to bother about implementing the __hash()__ and you know for certain that your object will never be hashed, you just explicitly declare __hash__ = None which takes care of the warning.

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