[Python-Dev] Add a frozendict builtin type

[Antoine Pitrou]

On Tue, 28 Feb 2012 12:07:32 +0000
Mark Shannon <mark at hotpy.org> wrote:
> Antoine Pitrou wrote:
> > On Tue, 28 Feb 2012 12:45:54 +0100
> > Victor Stinner <victor.stinner at haypocalc.com> wrote:
> >>> I think you need to elaborate on your use cases further, ...
> >> A frozendict can be used as a member of a set or as a key in a dictionary.
> >>
> >> For example, frozendict is indirectly needed when you want to use an
> >> object as a key of a dict, whereas one attribute of this object is a
> >> dict.
> > 
> > It isn't. You just have to define __hash__ correctly.
> > 
> >> frozendict helps also in threading and multiprocessing.
> > 
> > How so?
> 
> Inter process/task communication requires copying. Inter/intra thread
> communication uses reference semantics. To ensure these are the same,
> the objects used in communication must be immutable.

You just need them to be practically constant. No need for an immutable
type in the first place.

Regards

Antoine.