[Python-Dev] PEP 246, redux

[Phillip J. Eby]

At 01:50 PM 1/11/05 -0500, Clark C. Evans wrote:
>On Tue, Jan 11, 2005 at 12:54:36PM -0500, Phillip J. Eby wrote:
>| * Replacing LiskovViolation is possible by dropping type/isinstance
>| checks from adapt(), and adding an isinstance check to
>| object.__conform__; Liskov violators then override __conform__ in their
>| class to return None when asked to conform to a protocol they wish to
>| reject, and return super().__conform__ for all other cases.  This
>| achieves your use case while simplifying both the implementation and the
>| usage.
>
>I'd rather not assume that class inheritance implies substitutability,

Hm, you should take that up with Alex then, since that is what his current 
PEP 246 draft does.  :)  Actually, the earlier drafts did that too, so I'm 
not sure why you want to change this now.

What I've actually suggested here actually allows for 
inheritance=substitutability as the default, but also makes it trivially 
changeable for any given inheritance hierarchy by overriding __conform__ at 
the base of that hierarchy, and without introducing a special exception 
class to do it.