On 24 Sep 2013 08:09, "Greg Ewing" <greg.ew...@canterbury.ac.nz> wrote: > > Steven D'Aprano wrote: >> >> It might not be a rule, but it's certainly the norm. I reckon that class attributes that aren't accessible from the instance are significantly more surprising than Color.red.blue. > > > There are really two different kinds of things that we > refer to as "class attributes". One is things that really > are attributes of the class itself, and the other is > things that are meant to serve as default or shared > instance attributes. > > The confusion comes in because we use the same terminology > for both, and because Python doesn't provide any straightforward > way of creating user-defined class-only attributes,
Using @property in a metaclass definition isn't *that* complicated :) (says the guy who helps maintain the type system) > so > shared attributes tend to get abused for that purpose. > Then when someone comes along and creates a true > class-only attribute, people get all surprised and > complain about it. One of the interesting aspects of adding Enum has been the subtle descriptor handling bugs it has uncovered in the inspect module :) > They shouldn't, IMO. There's a helper for Enum's descriptors that will probably be exposed through the types module in the next 3.4 alpha (tentative name is types.DynamicClassAttribute). It's the inverse, though - it throws AttributeError when looked up on the *class* in order to trigger __getattr__ on the metaclass. Cheers, Nick. > > -- > Greg > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ncoghlan%40gmail.com
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