[Python-Dev] PEP 455: TransformDict (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Fri Sep 13 22:22:51 CEST 2013

On Fri, 13 Sep 2013 16:09:10 -0400 "R. David Murray" <rdmurray at bitdance.com> wrote:

On Fri, 13 Sep 2013 20:40:58 +0200, Antoine Pitrou <solipsis at pitrou.net> wrote: > Rationale > ========= > > Numerous specialized versions of this pattern exist. The most common > is a case-insensitive case-preserving dict, i.e. a dict-like container > which matches keys in a case-insensitive fashion but retains the > original casing. It is a very common need in network programming, as > many protocols feature some arrays of "key / value" properties in their > messages, where the keys are textual strings whose casing isn't > relevant.

This motivation would be stronger if the last phrase was something like "where the keys are textual strings whose case is specified to be ignored on receipt but by either specification or custom is to be preserved or non-trivially canonicalized when retransmitted."

Thanks, will add.

> (it can be said that the pattern projects keys from the user-visible > set onto the internal lookup set, hence this PEP's title)

Not clear what "projects" has to do with the PEP title.

The PEP was originally titled "a key-projecting dictionary" and I've changed it as it was too obscure. I've now also removed the obsolete part of the sentence above :-)

> Alternative proposals and questions > ===================================

You don't mention the alternate constructor discussion, or the rationale for following the defaultdict pattern (ie: following the established pattern :)

Ok, will do that too.

Regards

Antoine.

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