I should add that the previous checkin also added a slight

optimization for dynamic classes.  If __getattr__ is not found as an
attribute on the type, slot_tp_getattro replaces itself with
PyObject_GenericGetAttr.  This means you can't add a __getattr__
method to a class after the fact -- but you can still *change* a
__getattr__ method into a different one.

(A similar restriction exists for classic classes.)