I think it could inherit from the Mapping abc? class frozendict(Mapping): def __new__(cls, *args, **kwargs): d = dict(*args, **kwargs) proxy = MappingProxyType(d) instance = super().__new__(cls) instance.__proxy = proxy return instance def __hash__(self): return hash(tuple(self.items())) def __getattr__(self, name): return getattr(self.__proxy, name) def __getitem__(self, key): return self.__proxy[key] def __iter__(self): return self.__proxy.__iter__() def __len__(self): return len(self.__proxy) def __repr__(self): return "%s(%r)" % (type(self).__name__, dict(self)) On Tue, Oct 16, 2018 at 4:29 AM Steven D'Aprano <steve@pearwood.info> wrote:
On Tue, Oct 16, 2018 at 01:02:03AM -0700, George Leslie-Waksman wrote:
Would a frozendict require that keys and values be hashable?
Keys, yes. Values, no.
If the values were hashable, the frozendict itself would also be hashable. If not, then it would be like trying to hash a tuple with unhashable items:
py> hash((1, 2, {}, 3)) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unhashable type: 'dict'
It seems to me that we would need this restriction to make a reasonably universal frozendict that is, itself, hashable.
When people talk about frozendicts being hashable, they mean it in the same sense that tuples are hashable.
For what it is worth, here's an incomplete, quick and dirty proof of concept frozendict, using automatic delegation:
# Not good enough for production, not tested, buyer beware, etc. class frozendict: def __new__(cls, *args, **kwargs): d = dict(*args, **kwargs) proxy = types.MappingProxyType(d) instance = super().__new__(cls) instance.__proxy = proxy return instance def __hash__(self): return hash(tuple(self.items())) def __getattr__(self, name): return getattr(self.__proxy, name) def __getitem__(self, key): return self.__proxy[key] def __repr__(self): return "%s(%r)" % (type(self).__name__, dict(self))
-- Steve _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/