[Python-Dev] Re: PEP 246: LiskovViolation as a name

[Alex Martelli]

On 2005 Jan 13, at 02:18, Phillip J. Eby wrote:

> At 05:54 PM 1/12/05 -0700, Steven Bethard wrote:
>> Not that my opinion counts for much =), but returning None does seem
>> much simpler to me.  I also haven't seen any arguments against this
>> route of handling protocol nonconformance...  Is there a particular
>> advantage to the exception-raising scheme?
>
> Only if there's any objection to giving the 'object' type a default 
> __conform__ method that returns 'self' if 
> 'isinstance(protocol,ClassTypes) and isinstance(self,protocol)'.

In the spirit of minimalism in which I propose to rewrite PEP 246 (as 
per my latest post: make a simple, noninvasive, unassuming PEP 246 
while new ``copernical revolution'' ideas which you proposed mature in 
another PEP), I'd rather not make a change to built-in ``object''  a 
prereq for PEP 246; so, I think the reference implementation should 
avoid assuming such changes, if it's at all possible to avoid them 
(while, no doubt, indicating the desirability of such changes for 
simplification and acceleration).

Incidentally, "get this specialmethod from the type (with specialcasing 
for classic classes &c)" is a primitive that PEP 246 needs as much as, 
say, copy.py needs it.  In the light of the recent discussions of how 
to fix copy.py etc, I'm unsure about what to assume there, in a rewrite 
of PEP 246: that getattr(obj, '__aspecial__', None) always does the 
right thing via special descriptors, that I must spell everything out, 
or, what else...?

If anybody has advice or feedback on these points, it will be welcome!


Alex