[Python-Dev] PEP 416: Add a frozendict builtin type (original) (raw)

Jim J. Jewett jimjjewett at gmail.com
Thu Mar 1 05:33:21 CET 2012

In http://mail.python.org/pipermail/python-dev/2012-February/117113.html Victor Stinner posted:

An immutable mapping can be implemented using frozendict::

class immutabledict(frozendict): def new(cls, *args, **kw): # ensure that all values are immutable for key, value in itertools.chain(args, kw.items()): if not isinstance(value, (int, float, complex, str, bytes)): hash(value) # frozendict ensures that all keys are immutable return frozendict.new(cls, *args, **kw)

What is the purpose of this? Is it just a hashable frozendict?

If it is for security (as some other messages suggest), then I don't think it really helps.

class Proxy:
    def __eq__(self, other): return self.value == other
    def __hash__(self): return hash(self.value)

An instance of Proxy is hashable, and the hash is not object.hash, but it is still mutable. You're welcome to call that buggy, but a secure sandbox will have to deal with much worse.

-jJ

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If there are still threading problems with my replies, please email me with details, so that I can try to resolve them. -jJ

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