[Python-3000] Fixing super anyone?

[Guido van Rossum]

On 4/24/07, Steven Bethard <steven.bethard at gmail.com> wrote:
> class Super(object):
>     def __init__(self, type, obj=None):
>         if isinstance(obj, Super):
>             obj = obj.__obj__
>         self.__type__ = type
>         self.__obj__ = obj
>     def __get__(self, obj, cls=None):
>         if obj is None:
>             raise Exception('only supports instances')
>         else:
>             return Super(self.__type__, obj)
>     def __getattr__(self, attr):
>         mro = iter(self.__obj__.__class__.__mro__)
>         for cls in mro:
>             if cls is self.__type__:
>                 break
>         for cls in mro:
>             if attr in cls.__dict__:
>                 x = cls.__dict__[attr]
>                 if hasattr(x, '__get__'):
>                     x = x.__get__(self, cls)
>                 return x
>         raise AttributeError, attr
>
> class autosuper(type):
>     def __init__(cls, name, bases, clsdict):
>         cls.__super__ = Super(cls)
>
> class A:
>     __metaclass__ = autosuper
>     def f(self):
>         return 'A'
>
> class B(A):
>     def f(self):
>         return 'B' + self.__super__.f()
>
> class C(A):
>     def f(self):
>         return 'C' + self.__super__.f()
>
> class D(B, C):
>     def f(self):
>         return 'D' + self.__super__.f()
>
> assert D().f() == 'DBCA'

But:

class E(D): pass

print E().f()

This prints DDBCA which surely isn't right.

Sounds like the classic bug in such attempts.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)