[Python-Dev] Add a frozendict builtin type (original) (raw)

Guido van Rossum guido at python.org
Fri Mar 2 00:11:35 CET 2012

On Thu, Mar 1, 2012 at 12:35 PM, André Malo <nd at perlig.de> wrote:

* Guido van Rossum wrote:

On Thu, Mar 1, 2012 at 9:44 AM, Victor Stinner <victor.stinner at gmail.com> wrote: > frozendict would help pysandbox but also any security Python module, > not security, but also (many) other use cases ;-)

Well, let's focus on the other use cases, because to me the sandbox use case is too controversial (never mind how confident you are :-). I like thinking through the cache use case a bit more, since this is a common pattern. But I think it would be sufficient there to prevent accidental modification, so it should be sufficient to have a dict subclass that overrides the various mutating methods: setitem, delitem, pop(), popitem(), clear(), setdefault(), update(). For the caching part, simply making the dictproxy type public would already help a lot.

Heh, that's a great idea. Can you file a bug for that?

What other use cases are there? dicts as keys or as set members. I do run into this from time to time and always get tuple(sorted(items()) or something like that.

I know I've done that once or twice in my life too, but it's a pretty rare use case and as you say the solution is simple enough. An alternative is frozenset(d.items()) -- someone should compare the timing of these for large dicts.

-- --Guido van Rossum (python.org/~guido)

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