Hi Phillip,
On Mon, Jan 10, 2005 at 04:38:55PM -0500, Phillip J. Eby wrote:
> Your new proposal does not actually fix this problem in the absence of
> tp_conform/tp_adapt slots; it merely substitutes possible confusion at the
> metaclass/class level for confusion at the class/instance level.
I think that what Alex has in mind is that the __adapt__() and __conform__()
methods should work just like all other special methods for new-style classes.
The confusion comes from the fact that the reference implementation doesn't do
that. It should be fixed by replacing:
conform = getattr(type(obj), '__conform__', None)
with:
for basecls in type(obj).__mro__:
if '__conform__' in basecls.__dict__:
conform = basecls.__dict__['__conform__']
break
else:
# not found
and the same for '__adapt__'.
The point about tp_xxx slots is that when implemented in C with slots, you get
the latter (correct) effect for free. This is how metaconfusion is avoided in
post-2.2 Python. Using getattr() for that is essentially broken. Trying to
call the method and catching TypeErrors seems pretty fragile -- e.g. if you
are calling a __conform__() which is implemented in C you won't get a Python
frame in the traceback either.
A bientot,
Armin
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