An ordered dictionary for the Python library?

[Hamilton, William]

> From: Michele Simionato
> 
> On Sep 12, 3:54 pm, Mark Summerfield <m.n.summerfi... at googlemail.com>
> wrote:
> > On 12 Sep, 13:46, Michele Simionato <michele.simion... at gmail.com>
> >
> > Actually I meant by key order, so insertion order doesn't matter at
> > all. If you need a dictionary-like data structure that respects
> > insertion order you could use a list of (key, value) tuples.
> >
> > Another respondent asked about use cases.
> >
> > I have found time and again that I needed (key, value) pairs where
the
> > key is some string that provides a representation for human readers
> > and the value is some internal key (e.g., database ID) that the
system
> > uses internally. In these cases I often need to present the user
with
> > a list of items from which to choose and want to present them in
> > sorted order. Naturally, I could use an ordinary dict and then do
> > this:
> >
> > for string in sorted(d.keys()):
> >     process(string)
> >
> > But what happens when I need to do this a *lot* and when the number
of
> > items is hundreds or a few thousands? I'm having to sort again and
> > again, since it is often the case that the items in the list changes
> > during the runtime of the application. So my solution in C++ is to
use
> > an ordered dictionary (a map in C++ jargon), which in Python means I
> > can simply write:
> >
> > for string in od.keys():
> >     process(string)
> >
> 
> For your use case I would wrap a list [(key, value)] with a dict-like
> object and I would use the bisect module in the standard library to
> keep
> the inner list ordered.


Or subclass dict to carry along a sorted list of keys with it and return
that when dict.keys() is called.  Even better, only have .keys() sort
the keys list when a key has been added to it since the last call.


--
-Bill Hamilton