[Python-Dev] Add a frozendict builtin type

[André Malo]

On Thursday 01 March 2012 15:17:35 Serhiy Storchaka wrote:
> 01.03.12 11:29, André Malo написав(ла):
> > - Caching. My data container objects (say, resultsets from a db or
> > something) usually inherit from list or dict (sometimes also set) and are
> > cached heavily. In order to ensure that they are not modified
> > (accidentially), I have to choices: deepcopy or immutability. deepcopy is
> > so expensive, that it's often cheaper to just leave out the cache. So I
> > use immutability. (oh well, the objects are further restricted with
> > __slots__)
>
> This is the first rational use of frozendict that I see. However, a deep
> copy is still necessary to create the frozendict. For this case, I
> believe, would be better to "freeze" dict inplace and then copy-on-write
> it.

In my case it's actually a half one. The data mostly comes from memcache ;) 
I'm populating the object and then I'm done with it. People wanting to modify 
it, need to copy it, yes. OTOH usually a shallow copy is enough (here).

Funnily my ROList actually provides a "sorted" method instead of "sort" in 
order to create a sorted copy of the list.

nd