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From Objects/typeobject.c:
 /* The condition below could use some explanation.
 It appears that tp_new is not inherited for static types
 whose base class is 'object'; this seems to be a precaution
 so that old extension types don't suddenly become
 callable (object.__new__ wouldn't insure the invariants
 that the extension type's own factory function ensures).
 Heap types, of course, are under our control, so they do
 inherit tp_new; static extension types that specify some
 other built-in type as the default also
 inherit object.__new__. */
 if (base != &PyBaseObject_Type ||
 (type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
 if (type->tp_new == NULL)
 type->tp_new = base->tp_new;
 }