[Python-Dev] LinkedHashSet/LinkedHashMap equivalents

[Delaney, Timothy C (Timothy)]

Jeff Bauer wrote:

> I'm not specifically lobbying for its inclusion in
> stdlib, but I often find an ordered dict useful when I
> want both ordered and random access, e.g. situations:
> 
>    - database table fields/attributes
>    - drop down field selectors

Yep - these are also cases that are familiar to me - it's the type of
thing you don't think about until you actually need it.

> In both cases, I could get by with other techniques, but I
> would use stdlib ordered dicts if they were available.
> I also prefer the term "ordered dict" to LinkedHashXXX.

You may notice the subject is LinkedHashXXX *equivalents* ;) There is no
way I would ever propose adding them with those names.

OTOH, "ordered set" and "ordered dict" implies different things to
different people - usually "sorted" rather than "the order things were
put in". Perhaps "temporally-ordered" ;)

BTW, just to clarify the semantics:

Set: Items are iterated over in the order that they are added. Adding an
item that compares equal to one that is already in the set does not
replace the item already in the set, and does not change the iteration
order. Removing an item, then re-adding it moves the item to the end of
the iteration order.

Dict: Keys are iterated over in the order that they are added. Setting a
value using a key that compares equal to one already in the dict
replaces the value, but not the key, and does not change the iteration
order. Removing a key (and value) then re-adding it moves the key to the
end of the iteration order.

Tim Delaney