Why are there no ordered dictionaries?

[bonono at gmail.com]

Christoph Zwerschke wrote:
> Fredrik Lundh wrote:
> > I'll repeat this one last time: for the use cases presented by Zwerschke
> > and "bonono", using a list as the master data structure, and creating the
> > dictionary on demand, is a lot faster than using a ready-made ordered
> > dict implementation.  if you will access things via the dictionary a lot,
> > you can cache the dictionary somewhere.  if not, you can recreate it
> > several times and still get a net win.
>
> You're right in pointing out that the advantage of ordered dictionaries
> (unless you use an omptimized C implementation) is not a performance gain.
>
> But please see my other reply: If the dictionary has more than 3 items
> (say 10 or 20), and an effective ordered dict is used, it's not really
> "a lot" slower. At least if we are talking about a situation were "on
> demand" is "always". So, on the other side there isn't such a big
> performance loss when using ordered dictionaries as well.
>
> The advantage of using an ordered dictionary is that you can set up your
> ordered dictionary (say, describing your database columns) once, and
> then can access it in any way you like in the following: Iterate over it
> in a guaranteed order or access item, always refering to the same
> object, without needing to care about building and caching auxiliary
> objects with different names depending on what you are doing.
>
Well, I don't think performance is the concern(at least not for me),
but how best to blend with the rest of the code which I have no
interest to explain as I am not here to convincing anyone for such a
thing. I just present a use case, if they see it, fine. If not, that is
fine too.

But I did learn something that creating a dict on a list cost me
nothing, I would be less worry about the performance hit in the future.