Why are there no ordered dictionaries?

[Fredrik Lundh]

"Fuzzyman" wrote:

> [snip..]
> > (as an example, on my machine, using Foord's OrderedDict class
> > on Zwerschke's example, creating the dictionary in the first place
> > takes 5 times longer than the index approach, and accessing an
> > item takes 3 times longer.  you can in fact recreate the index 6
> > times before OrderedDict is faster; if you keep the index around,
> > the OrderedDict approach never wins...)
>
> So, so long as you want to use the dictionary less than six times -
> it's faster to store/access it as a list of tuples. ;-)

nope.  that's not what I said.  I said that you can recreate the index
six times in the time it takes to create a single OrderedDict instance.
if you need to use index more than that, it's not that hard to keep a
reference to it.

> Everytime you want to access (or assign to) the data structure as a
> dictionary, you have to re-create the index.

the use case we're talking about here (field descriptors) doesn't involve
assigning to the data structure, once it's created.

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.

for other use cases, things may be different, but nobody has presented
such a use case yet.  as I said earlier, "let's assume we have another use
case" is not a valid use case.

</F>