Attached is a simple example; yes, a bit contrived, but
it's exactly what bit me in the ass for a week or two :)

nestled within abstract.c's recursive_isinstance, is
this lil nugget-

icls = PyObject_GetAttr(inst, __class__);
if (icls == NULL) {
  PyErr_Clear();
  retval = 0;
}
else {

No surrouding comments to indicate *why* it's
swallowing exceptions, but best explanation I've heard
was that it was attempting to swallow just
AttributeError... which would make sense.

So the question is, whats the purpose of it swallowing
exceptions there?  Bad form of AttributeError catching,
or some unstated reason?