[Python-Dev] ABC issues

Georg Brandl g.brandl at gmx.net
Sat Jun 7 20:16:16 CEST 2008

Guido van Rossum schrieb:
> On Mon, May 26, 2008 at 11:59 AM, Raymond Hettinger <python at 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.
> We could make the incompatible mixin classes available separately
> though, if you think they're useful.
>>> * The 2.6 UserDict is not registered as a mapping.
>> Since the API's are not currently the same, it makes
>> sense that UserDict is not registered.
>> If the Mapping ABC does get changed, only IterableUserDict
>> should get registered.  A regular UserDict does not comply.
> Fair enough. I recomment to fix the Mapping ABC and register IterableUserDict.

As a followup:
- The Mapping fix is in http://bugs.python.org/issue3057.
- Registering IterableUserDict is now in SVN.


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