您可以设置依赖于另一个字典条目的字典值吗? [英] Can you set a dictionary value dependant on another dictionary entry?

问题描述

我的想法是这样的:

dict1 = {key1:3, key2:5, key3:key1+key2}
# so key3 relate to the value: 8 (3+5)
dict1.update({key2:6})
# key3 will now relate to the value: 9 (3+6)

我试图避免更新不必要的条目，并基于在比较关系值时已经在一系列查找和更新中计算的值构建新的键值关系.字典的哈希性对于让我在查找时或多或少保持恒定时间至关重要.

I'm trying to avoid updating more entries than necessary as well as building new relations of key-value that's based on values that has already been calculated in a series of lookups and updates while comparing values of relations. The dictionarys' hashability is crucial to get me a more or less constant time on lookup.

推荐答案

这不是通用解决方案，但大致适用于您的示例:

This isn't a general solution but roughly works for your example:

class DynamicDict(dict):
    def __getitem__(self, key):
        value = super(DynamicDict, self).__getitem__(key)
        return eval(value, self) if isinstance(value, str) else value

>>> d = DynamicDict(key1=3, key2=5, key3='key1+key2')
>>> d.update({'key2': 6})
>>> d['key3']
9

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