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 possible! I belive this is a bug fix candidate for Python 2.2.2.
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