On Tue, May 27, 2008 at 10:44 AM, Raymond Hettinger <python@rcn.com> wrote:
* The 2.6-backported Mapping ABC has the 3.0 dict API, that is, it uses keys() that returns a view etc.
Curious to hear what Guido thinks about this one. A nice use of the Mapping ABC is to be able to get 3.0 behaviors. I thought that was the whole point of all these backports. If the ABC gets altered, then it just makes the 2-to-3 conversion harder.
It's wrong if the ABC doesn't describe the behavior of actual implementations; that is its primary purpose, the mixin class is a nice side benefit.
ISTM, the one purpose of backporting is to make 2.6 closer to 3.0. Altering the API will just make them further apart.
Well, the ABCs have two sides -- they describe the API and they provide a mix-in. I feel strongly that the primary function of ABCs is to describe the API (in fact many ABCs do only that, e.g. look at Sized and Container). I want isinstance({}, collections.Mapping) to be true. If you want to use the 3.0 mixins in 2.6, perhaps an alternate set of APIs could be imported from the future? E.g. from future_collections import Mapping. IIRC a similar mechanism was proposed for some built-in functions, even though I see no traces of an implementation yet. -- --Guido van Rossum (home page: http://www.python.org/~guido/)