In Objects/dictobject.c, if I remove the INCREF/DECREF pair around PyObject_RichCompareBool(), all the tests still pass:

-           Py_INCREF(startkey);
            cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
-           Py_DECREF(startkey);

It would be nice to have tests demonstrating why it is necessary.  IIRC the reason is that an object could have a custom comparison that clears the enclosing container and frees the element during the comparison.  

Also, it would be nice if PyObject_RichCompareBool() could be redesigned to not fail if a borrowed reference gets deallocated while the function is running.  The incref and decref occur on a hot path, and it is unfortunate that they cause extra writes to objects scattered all over memory, likely causing a lot of cache misses in real programs.