[Python-3000] PEP 3119 - Introducing Abstract Base Classes

[Tony Lownds]

On Apr 27, 2007, at 10:40 AM, Bill Janssen wrote:

> Jim Jewett wrote:
>> On 4/27/07, Barry Warsaw <barry at python.org> wrote:
>>
>>> - - Attributes.  Interfaces allow you to make assertions about
>>> attributes, not just methods, while ABCs necessarily cover only  
>>> methods.
>>
>> Why can't they have data attributes as well?
>
> I agree with Jim.  It seems to me that documenting standard attributes
> of a type is one thing that ABC's should be able to do.  Perhaps a
> "@abstractattribute" decorator of some sort?  Perhaps a class  
> decorator
> "@attributes(name1, name2, ...)"?  Attributes with those names  
> would be
> automatically added to an instance, initialized to None, before the
> first __init__ method would be called.

+0 on abstract attributes. Methods seem to dominate most APIs that make
use of interfaces, but there are always a few exceptions.

Attribute annotations could provide an elegant solution here.

class ABC:
   concrete_attribute : "any expression" = None
   abstract_attribute : "any expression"

I posted about attribute annotations before on python-ideas and there  
was
lukewarm response. If anyone thinks a PEP on attribute annotations is  
worth
submitting, let me know.

Thanks
-Tony