That is interesting. From my recollection, when OrderedDict was reimplemented in C, there was advice on the thread to not implement it as a subclass of dict.
https://bugs.python.org/issue16991 I'm far from the right person to comment on the exact reasons, but perhaps frozenset being decoupled from set gives precedence for a frozendict not subclassing dict? The methods clear, pop, popitem, update and setdefault would not be necessary. On Wed, Oct 10, 2018 at 9:28 PM Chris Angelico <ros...@gmail.com> wrote: > On Thu, Oct 11, 2018 at 1:02 PM Cameron Simpson <c...@cskk.id.au> wrote: > > > > On 10Oct2018 20:25, Philip Martin <philip.martin2...@gmail.com> wrote: > > >Steven, that's a great idea, and I would be 100% up for your suggestion > to > > >have types.MappingProxyType renamed to frozendict. > > > > I'm not for the rename, myself. Though I'd not be against a frozendict > > factory in builtins, a tiny shim for MappingProxyType. > > > > >However, the differences > > >in the behavior of MappingProxyType's constructor versus dict's would > make > > >the API's behavior confusing IMO. For example, MappingProxyType(x=5, > y=10) > > >throws a TypeError. I don't think most people would expect this. > > > > Well, if it were called frozendict, indeed not. It should act like dict. > > > > So: > > > > def frozendict(**kw): > > return MappingProxyType(kw) > > > > You could make an argument for that (or a slightly heftier version > > accepting the various things dict accepts). Or... you could just keep > > such a thing in your personal kit as a trivial way to spell > > "frozendict". One could argue for the above as a nice example to live in > > the docs perhaps. > > > > But not everything needs a special name. > > > > Point of note: A mapping proxy is NOT immutable; it is merely read-only. > > >>> from types import MappingProxyType > >>> d = {'a':1, 'b':2} > >>> p = MappingProxyType(d) > >>> p > mappingproxy({'a': 1, 'b': 2}) > >>> d['a'] = 3 > >>> p > mappingproxy({'a': 3, 'b': 2}) > > A frozendict type, if it's meant to parallel frozenset, ought to be > hashable (subject to the hashability of its members, of course), but > you can't just take MPT and toss in a __hash__ method. No idea how > important that use-case is, but Michael Selik mentioned "want[ing] to > use a dict as a dict key about once or twice a year", which MPT is not > able to do. > > Interestingly, frozenset isn't a subclass of set. I was going to say > that a frozendict ought to be a dict, but maybe that isn't so > important. Which might make a simple pure-Python frozendict actually > pretty easy. > > ChrisA > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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