[Python-Dev] Strange bug only happens with Python 2.2
Guido van Rossum
Fri, 27 Sep 2002 20:11:54 -0400
> Ok, I've now further narrowed down this isinstance issue:
> python22-maint ==> bug does not appear
> python22-maint with abstract.c from Python 2.2.1 ==> bug appears
> So for what it's worth (i. e. not much), I'd say please /do/ include the
> abstract.c changes into the upcoming Python 2.2.2 :-)
I'm sure it's this change, which was backported to the 2.2 maintenance
branch (and hence will be in 2.2.2). It fixes several several
occurrences where an error is not cleared.
date: 2002/04/23 22:45:44; author: bwarsaw; state: Exp; lines: +46 -9
abstract_get_bases(): Clarify exactly what the return values and
states can be for this function, and ensure that only AttributeErrors
are masked. Any other exception raised via the equivalent of
getattr(cls, '__bases__') should be propagated up.
abstract_issubclass(): If abstract_get_bases() returns NULL, we must
call PyErr_Occurred() to see if an exception is being propagated, and
return -1 or 0 as appropriate. This is the specific fix for a problem
whereby if getattr(derived, '__bases__') raised an exception, an
"undetected error" would occur (under a debug build). This nasty
situation was uncovered when writing a security proxy extension type
for the Zope3 project, where the security proxy raised a Forbidden
exception on getattr of __bases__.
PyObject_IsInstance(), PyObject_IsSubclass(): After both calls to
abstract_get_bases(), where we're setting the TypeError if the return
value is NULL, we must first check to see if an exception occurred,
and /not/ mask an existing exception.
Neil Schemenauer should double check that these changes don't break
his ExtensionClass examples (there aren't any test cases for those
examples and abstract_get_bases() was added by him in response to
problems with ExtensionClass). Neil, please add test cases if
I belive this is a bug fix candidate for Python 2.2.2.
--Guido van Rossum (home page: http://www.python.org/~guido/)