[Python-ideas] An identity dict

[Nick Coghlan]

On 30/05/10 13:27, Benjamin Peterson wrote:
> In the spirit of collections.OrderedDict and collections.defaultdict, I'd like
> to propose collections.identitydict. It would function just like a normal
> dictionary, but ignore hash values and comparison operators and merely lookup
> keys based on the key's id().
>
> This dict is very useful for keep track of objects that should not be compared
> by normal comparison methods. For example, I would use an identitydict to hold
> weak references that would otherwise fallback to their referant object's hash.
>
> An advantage of formalizing this in collections would be to enable other Python
> implementations like PyPy, where id() is expensive, to provide an optimized
> identitydict.

How would dict equality be defined? In terms of values, or in terms of 
value identity?

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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