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pythondictionarydata-structureslanguage-agnostic
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Reputation: 60014

A dictionary with a unique possible value for each key?

I need to create a map from twitter status IDs to their author ID. Obviously, each status has exactly one author.

I expected Python collections to have something like uniqdict class for which d[key] = value will raise an exception if the key already has a value different from value:

class uniqdict(dict):
    def __setitem__(self,key,value):
        try:
            old = super(uniqdict,self).__getitem__(key)
            if old != value:
                raise ValueError(self.__class__.__name__,key,old,value)
        except KeyError:
            super(uniqdict,self).__setitem__(key,value)

Q: Is there a standard name for this kind of dictionary/map/hash table?

Upvotes: 8

Views: 179

Answers (2)

Shmulik Asafi
Shmulik Asafi

Reputation: 203

This looks like a duplicate of Write-once dictionary?

Anyway, I think write-once dictionary is the name you're looking for

Upvotes: 1

MarnixKlooster ReinstateMonica
MarnixKlooster ReinstateMonica

Reputation: 9739

I had a similar requirement recently, where I needed to merge two dicts but it was an error if they had any keys in common.

I don't think there is a standard name, so let me propose one: a no-overwrite dictionary.

Or perhaps single-update keys dictionary, but that's a bit ugly.

(The simpler alternative single-update dictionary seems too misleading.)

Upvotes: 0

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