缺少Python的冻结字典类型的解决方法? [英] A workaround for Python's missing frozen-dict type?

问题描述

在Python中，当您想将列表用作某些字典的键时，可以将它们变成元组，它们是不可变的，因此是可哈希的.

In Python, when you want to use lists as keys of some dictionary, you can turn them into tuples, which are immutable and hence are hashable.

>>> a = {}
>>> a[tuple(list_1)] = some_value
>>> a[tuple(list_2)] = some_other_value

当您要使用 set 对象作为某些字典的键时，也会发生同样的情况-您可以构建一个 frozenset ，它又是不可变的，因此是可哈希的.

The same happens when you want to use set objects as keys of some dictionary - you can build a frozenset, that is again immutable and hence is hashable.

>>> a = {}
>>> a[frozenset(set_1)] = some_value
>>> a[frozenset(set_2)] = some_other_value

但是似乎字典没有对应的内容.

But it seems that for dictionary there is no equivalent.

我想到的第一个想法(最终发现它很糟糕)是使用str(some_dict)作为键.但是，字典始终使用不同的哈希函数，因此，相等字典的字符串可能会有所不同.

A first idea I thought about (and found it bad finally), is to use str(some_dict) as a key. But, dictionaries always use different hash functions, so strings of equal dictionaries may be different.

有没有一种好的方法，或者有人有其他想法如何将类似字典的对象用作其他字典的键?

Is there any workaround known as a good practice, or does anyone have other ideas how to use dictionary-like objects as keys of other dictionaries?

推荐答案

我找到了解决此问题的好方法，它正在构建包含字典项的 frozenset :

I've found a nice workaround for this problem, which is building a frozenset containing the dictionary items:

>>> a = {'key1' : 'val1', 'key2' : 'val2'}
>>> b = frozenset(a.items())
>>> frozenset_restored_to_dict = dict(b)
>>> frozenset_restored_to_dict
{'key2': 'val2', 'key1': 'val1'}

从代码中可以看出，b是一个冻结集，它是不可变的且可哈希的，并且可以完全还原为像a这样的常规词典.

As can be seen in the code, b is a frozenset, which is immutable and hashable, and can be totally restored to be a regular dictionary like a.

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