[Python-Dev] PEP 246, redux

[Michael Hudson]

Alex Martelli <aleax at aleax.it> writes:

> I didn't know about the "let the object lie" quirk in isinstance.  If
> that quirk is indeed an intended design feature, rather than an
> implementation 'oops', it might perhaps be worth documenting it more
> clearly; I do not find that clearly spelled out in the place I'd
> expect it to be, namely
> <http://docs.python.org/lib/built-in-funcs.html> under 'isinstance'.

Were you not at the PyPy sprint where bugs in some __getattr__ method
caused infinite recursions on the isinstance's code attempting to
access __class__?  The isinstance code then silently eats the error,
so we had (a) a massive slowdown and (b) isinstance failing in an
"impossible" way.  A clue was that if you ran the code on OS X with
its silly default stack limits the code dumped core instead of going
slowly insane.

This is on quirk I'm not likely to forget in a hurry...

Cheers,
mwh

-- 
  If trees could scream, would we be so cavalier about cutting them
  down? We might, if they screamed all the time, for no good reason.
                                                        -- Jack Handey