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 <mertz@gnosis.cx> 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 <levkivskyi@gmail.com> 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 <josephhackman@gmail.com> 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 < desmoulinmichel@gmail.com> 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.
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