[Python-ideas] OrderedDict.insert()

[Andrew Barnert]

On Mar 25, 2015, at 04:00, Thomas Güttler <guettliml at thomas-guettler.de> wrote:
> 
> I am missing OrderedDict.insert()

With what interface? Does it take an index, like list.insert, even though other OrderedDict methods (including __getitem__ and friends) don't? Or does it take another key? If so, does it insert before or after that key? And what if that key doesn't exist? Meanwhile, if the new key was already in the dict, should it move to the new position, update values in place, or raise an exception? Do you expect O(1) performance?

> Other people, too:
> 
>  http://stackoverflow.com/questions/16664874/how-can-i-add-the-element-at-the-top-of-ordereddict-in-python

That other person is asking for some way to put a new element on the left instead of the right, which doesn't have any of those issues. (And which is already possible with move_to_end.) And an anonymous low-rep user asking a question, getting a handful of upvotes, and accepting an answer that says "You can't, just build a new dict" with no comment doesn't exactly show a burning desire within a wide community.

In fact, I think this does a better job showing how OrderedDict is often an attractive nuisance than how it's incomplete--the guy can't explain why he wants this, and meanwhile he apparently thinks you have to build a new dict and call update to add a value (or at least that doing so should have a different result than just using __setitem__ with that new key and value). My guess is that either he didn't really want an OrderedDict in the first place, or Zagorulkin Dmitri is right that the real problem is that his program needs this feature and it should be rewritten so it doesn't. But without actually knowing the use case that's just a guess.

> Why was it not implemented up to now?
> 
> Why not implement it for the future?
> 
> Regards,
>  Thomas Güttler
> 
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