On 9/10/2013 2:46 PM, Antoine Pitrou wrote:
> >>Which reminds one - this class should obviously have a method for
> >>retrivieng the original key value, given a matching key -
> >>
> >>d.canonical('foo') -> 'Foo'
> >
> >I don't know. Is there any use case?
> >(sure, it is trivially implemented)
>
>
>Well, I'd expect it to simply be there. I had not thought of
>other usecases for the transformdict itself -
Well, it is not here for dict, set, etc.
But they don't change the keys (although numbers have different
representations on occasion).
One use of transformdict might be to allow use of non-hashable items as
keys, by extracting an actual key from the internals of the non-hashable
item. The key may be sufficiently unique to enable use of the dict
structure for lookups, but it would certainly be handy to obtain the
actual item again. Without a canonical lookup feature, one would be
forced to also include the key as part of the value, or some such hack.
I also thought João's example was a very practical reason to have the
canonical lookup feature, by some name or another.
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