[kj] > The implication here is that .update() does not in turn use > .__setitem__(), which I find a bit surprising.
It's never wise to make assumptions about this sort of thing. Every method in a class or type is allowed to directly access or modify its private, internal data. The implementation is free to choose whether to limit that access to a few accessors (i.e. getitem, setitem, delitem, len) or to let all of the methods have direct access to the underlying data structure. Even if accessors were used, the choice would be arbitrary (perhaps delitem() gets implemented in terms of pop() or somesuch). This is a basic for OO programming. Unless the class documentation promises to use particular hooks, the implementation is free to change in any way that doesn't violate the published API (this is one of the benefits of encapsulation and abstract data types). In general, if a subclass is overriding, rather than extending, then it should override *every* method that could be affected. Raymond -- http://mail.python.org/mailman/listinfo/python-list
