[Python-Dev] PEP 351, the freeze protocol (original) (raw)

Josiah Carlson jcarlson at uci.edu
Tue Oct 25 21:04:33 CEST 2005

Nick Coghlan <ncoghlan at gmail.com> wrote:

Josiah Carlson wrote: > Nick Coghlan <ncoghlan at gmail.com> wrote: >> I think having dicts and sets automatically invoke freeze would be a mistake, >> because at least one of the following two cases would behave unexpectedly: > > I'm pretty sure that the PEP was only aslomg if one would freeze the > contents of dicts IF the dict was being frozen. > > That is, which of the following should be the case: > freeze({1:[2,3,4]}) -> {1:[2,3,4]} > freeze({1:[2,3,4]}) -> xdict(1=(2,3,4)) I believe the choices you intended are: freeze({1:[2,3,4]}) -> imdict(1=[2,3,4]) freeze({1:[2,3,4]}) -> imdict(1=(2,3,4)) Regardless, that question makes a lot more sense (and looking at the PEP again, I realised I simply read it wrong the first time). For containers where equality depends on the contents of the container (i.e., all the builtin ones), I don't see how it is possible to implement a sensible hash function without freezing the contents as well - otherwise your immutable isn't particularly immutable. Consider what would happen if list "freeze" simply returned a tuple version of itself - you have a freeze method which returns a potentially unhashable object!

I agree completely, hence my original statement on 10/23: "it is of my opinion that a container which is frozen should have its contents frozen as well."

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