it seems the code of PyObject_GenericGetAttr, which invokes the
descriptor protocol, silences any AttributeErrors raised by the
descriptor, for classes that also define __getattr__. it should
propagate up rather than being silently ignored.

the attached example is quite artificial, but it's a simplification of
real world code i had hard time debugging. turned out i misspelled an
attribute name inside the property getter function, which raised an
AttributeError as expected -- but the exception i got was quite
misleading, saying the instance has no attribute named so.

this bug only happens when the class defines a custom __getattr__. see
attached demo file for details.