Python设置1和True的interpetation

2022-01-17 00:00:00 python set

问题描述

在 IPython 3 交互式外壳中:

In IPython 3 interactive shell:

In [53]: set2 = {1, 2, True, "hello"}

In [54]: len(set2)
Out[54]: 3

In [55]: set2
Out[55]: {'hello', True, 2}

这是因为 1 和 True 得到相同的交互作用，所以假设 set 消除了重复项，那么只有其中一个 (True) 可以保留?我们如何才能两者兼得?

Is that because 1 and True get the same interpetation so given that set eliminates duplicates, only one of them (True) gets to stay? How can we keep both?

解决方案

集合是 hashables.即使语句 1 is True 是 False，语句 1 == True 也是 True.因此，它们具有相同的哈希值，不能单独存在于一个集合中，并且你不能将它们都放在一个集合中

A set is a collection of hashables. Even though the statement 1 is True is False, the statement 1 == True is True. Because of that, they have the same hash value and cannot exist separately in a set, and you cannot keep them both in a set

EDIT 明确地说，正如 jme 指出的那样，这是因为两件事都是真实的——它们是相等的(每个 __eq__)并且它们具有相同的 哈希值(每个 __hash__).

EDIT To make it explicit, as jme pointed out, it is because BOTH things are true - they are equal (per __eq__) AND they have the same hash value (per __hash__).

在一个完美的世界中，相等的对象也将具有相同的哈希值，幸好这对于内置类型是正确的.

In a perfect world, equal objects would also have the same hash value, and thankfully this is true for built-in types.

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