Ah, I think I figured it out - in 2.x, PyObject_Hash itself includes the
fallback to _PyHash_Pointer if none of tp_hash, tp_compare or the
tp_richcompare slots have been implemented on the type.

So long as a type is only trying to inherit object.__hash__ (as is the
case with xrange), then this fallback will do the right thing if
PyType_Ready hasn't been called yet.

In 3.0, on the other hand, PyObject_Hash has no fallback - if tp_hash
isn't filled in, the type isn't considered hashable. This means that for
a type to properly inherit hashability in Py3k, PyType_Ready *must* be
called on it.

Probably the best thing to do is to add xrange and range to the list of
types initialised in _Py_ReadyTypes in 2.x and 3.x respectively.