[Python-3000] ordered dict for p3k collections? (original) (raw)

Mark Summerfield mark at qtrac.eu
Tue Sep 25 10:58:03 CEST 2007

On 2007-09-16, Arvind Singh wrote:

> How do you get from "some keys can't be ordered" to "it doesn't make > sense for Python to have sorteddict or sortedset"? If you want to use > keys that can't be ordered, then feel free to continue to use dict. > For situations in which ordering is important, that language should > support that. When did this become an all or nothing proposition? > There's plenty of space for both dict and sorteddict.

Sorry for premature conclusions. All I wanted to do was remind the potential problems with any "generic" implementation. And I did say, when ordering is important, we are left with two choices: 1) Sort explicitly (whenever required) and be prepared to handle exceptions raised during sort operation. 2) Have a implicitly "sorted" implementation and handle exceptions at every insertion. I, personally, tend to prefer the former solution. Later case is useful when we have large objects and we do large number of insertions, in which case, per insertion exception handling would be inefficient. Former case, in turn, can be slightly confusing and a bit to debug.

I can understand your personal preference for dict, although mine is for sorteddict---but IMO Python should provide both since both are legitimate in appropriate contexts. To this end I've put a posting on comp.lang.python with subject:

sorteddict PEP proposal [started off as orderedict]

If there is a positive response I will submit it to the PEP editors. If there is not, I will just hope that someone else will pick up the idea, even if in another form or with a different API, because I'd really like to see some kind of sorted dictionary in Python's standard library. (I also think there's a similar case for a sorted set.)

-- Mark Summerfield, Qtrac Ltd., www.qtrac.eu

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