I've implemented `frozendict` a few times for various projects and never knew about MappingProxyType. I always used `collections.abc.Mapping` ...
On Tue, Feb 28, 2017 at 9:12 AM, David Mertz <[email protected]> wrote: > The difference in hits might be because MappingProxyType has a funny name > and is in a hidden-ish location. I.e. not necessarily because it *would > be* less used or useful if it were more exposed. > > It also might be because you can use `frozenset` in python2.x code -- And there's lots of that lying around... > In either case, the name that makes sense to me would be `frozendict`. > That could very well live in `collections` of course. > Yes, I agree. Though it'd also probably need to be hashable if we were to give it that name. I'm not 100% sure that `MappingProxyType` works there as it's just a view into another mapping. If the first mapping changes, so does the hash. This is the same problem we have hashing tuple in some sense -- But tuple can say "Nope, sorry. I can't hash this because it's got an unhashable member". I don't think we can really do the same thing with a MappingProxy since most of the time, it'll be constructed from something else. I suppose the workaround is pretty simple though: class frozendict(MappingProxyType): def __init__(self, proxy): super().__init__(proxy.copy()) # Copy the proxy! -- Maybe need `copy.copy()` instead? def __hash__(self): return hash(frozenset(self.items())) This could likely be done better, but hopefully it gets the idea across... > > On Tue, Feb 28, 2017 at 7:40 AM, Ivan Levkivskyi <[email protected]> > wrote: > >> Searching MappingProxyType on GitHub gives over 10,000 results. >> I think it probably makes sense to make mappingproxy more "visible", >> maybe move it to collections module? (where OrderedDict lives) >> >> I am not sure if it makes sense to move it to builtins. (for comparison >> frozenset gives around 1000,000 results) >> >> -- >> Ivan >> >> >> >> On 28 February 2017 at 16:24, Joseph Hackman <[email protected]> >> wrote: >> >>> +1 >>> >>> I think this makes a lot of sense. What would you name the built in? >>> >>> -Joseph >>> >>> > On Feb 28, 2017, at 7:17 AM, Michel Desmoulin < >>> [email protected]> wrote: >>> > >>> > We have the immutable frozenset for sets and and tuples for lists. >>> > >>> > But we also have something to manipulate dict as immutable >>> datastructures: >>> > >>> >>>> from types import MappingProxyType as idict >>> >>>> d = idict({'a':1, 'b':2, 'c':3}) >>> >>>> d['a'] = 4 >>> > Traceback (most recent call last): >>> > File "<ipython-input-3-c6f93d6278af>", line 1, in <module> >>> > d['a'] = 4 >>> > TypeError: 'mappingproxy' object does not support item assignment >>> > >>> > We could expose this as a built type to allow the last of the most >>> > important data structure in Python to be easily immutable. >>> > >>> > _______________________________________________ >>> > Python-ideas mailing list >>> > [email protected] >>> > https://mail.python.org/mailman/listinfo/python-ideas >>> > Code of Conduct: http://python.org/psf/codeofconduct/ >>> _______________________________________________ >>> Python-ideas mailing list >>> [email protected] >>> https://mail.python.org/mailman/listinfo/python-ideas >>> Code of Conduct: http://python.org/psf/codeofconduct/ >>> >> >> >> _______________________________________________ >> Python-ideas mailing list >> [email protected] >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > > > > -- > Keeping medicines from the bloodstreams of the sick; food > from the bellies of the hungry; books from the hands of the > uneducated; technology from the underdeveloped; and putting > advocates of freedom in prisons. Intellectual property is > to the 21st century what the slave trade was to the 16th. > > _______________________________________________ > Python-ideas mailing list > [email protected] > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > -- [image: pattern-sig.png] Matt Gilson // SOFTWARE ENGINEER E: [email protected] // P: 603.892.7736 We’re looking for beta testers. Go here <https://www.getpattern.com/meetpattern> to sign up!
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