[Python-ideas] Identity dicts and sets

[Antoine Pitrou]

On Thu, 3 Jan 2013 13:37:40 +1000
Nick Coghlan <ncoghlan at gmail.com> wrote:
> On Thu, Jan 3, 2013 at 8:48 AM, Terry Reedy <tjreedy at udel.edu> wrote:
> > On 1/2/2013 9:01 AM, Serhiy Storchaka wrote:
> >>
> >> I propose to add new standard collection types: IdentityDict and
> >> IdentitySet. They are almost same as ordinal dict and set, but uses
> >
> >
> > What do you mean by ordinal dict, as opposed to plain dict.
> 
> I assumed Serhiy meant OrderedDict.

I'm quite sure Serhiy meant ordinary dict.

> As noted elsewhere, we already have a nasty composition
> problem between __missing__, order preservation and weak referencing.

Aren't you dramatizing a bit? I haven't seen anyone ask for an ordered
weak dict, or a weak dict with default values.

> So, -1 from me on making the composition problem worse, but tentative
> +0 on an API that addresses the composition problem and also includes
> "key=func" style support for using a decorated value in the lookup
> step.

Well, IdentityDict addresses an actual use case. I don't think a
defaultidentitydict addresses any use case.

Regards

Antoine.