[Python-Dev] PEP 372 -- Adding an ordered directory to collectionsready for pronouncement

[Barry Warsaw]

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Raymond,

+1 on adding this to the stdlib.  I especially like the idea of being  
able to use an ordered dict in a class's namespace.  I might be able  
use something like that to make my enum package simpler (which  
currently requires assignment of the name to the integer sort order).

I wanted to point out that the email package uses an ordered  
dictionary in its Message implementation.  Messages present a  
dictionary-like API for its headers.  I don't think I'd be able to use  
odicts though for this because of other semantic differences, e.g.  
multiple keys are allowed (though only visible through the non-mapping  
interface) and KeyError is never raised (like a defaultdict with a  
__missing__() returning None).  Note though that Message's odict-like  
implementation is about as horribly gross as it can be: it's just a  
list with linear searching for key lookup.  Messages should not have a  
billion headers. ;)

Have you or Armin considered the possibility of wanting both the  
defaultdict and odict behavior in, say a mixin subclass?

Barry

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