实现__hash __（）的正确和好办法是什么？ [英] What's a correct and good way to implement __hash__()?

问题描述

实现 __ hash __（）？

我正在谈论的功能是什么？返回一个哈希码，然后用于将对象插入散列哈希表字典中。

I am talking about the function that returns a hashcode that is then used to insert objects into hashtables aka dictionaries.

As __ hash __（）返回一个整数并且用于将对象binning到散列表中我假定返回的整数的值应该为普通数据均匀分布（以最小化冲突）。
得到这样的价值是什么好习惯？碰撞有问题吗？
在我的情况下，我有一个小类，作为一个容器类，它持有一些int，一些浮点和一个字符串。

As __hash__() returns an integer and is used for "binning" objects into hashtables I assume that the values of the returned integer should be uniformly distributed for common data (to minimize collisions). What's a good practice to get such values? Are collisions a problem? In my case I have a small class which acts as a container class holding some ints, some floats and a string.

推荐答案

实现 __ hash __（）的简单，正确的方法是使用一个关键的元组。它不会像专门的哈希一样快，但如果需要，那么你应该可以在C中实现类型。

An easy, correct way to implement __hash__() is to use a key tuple. It won't be as fast as a specialized hash, but if you need that then you should probably implement the type in C.

这里是一个使用键的例子哈希和平等：

Here's an example of using a key for hash and equality:

class A(object):
    def __key(self):
        return (self.attr_a, self.attr_b, self.attr_c)

    def __eq__(x, y):
        return x.__key() == y.__key()

    def __hash__(self):
        return hash(self.__key())

此外， __ hash __ 有更多的信息，这在某些特定情况下可能是有价值的。

Also, the documentation of __hash__ has more information, that may be valuable in some particular circumstances.

这篇关于实现__hash __（）的正确和好办法是什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！