[Persistence-sig] A simple Observation API

[Guido van Rossum]

Some questions about Phillip's Observable protocol.  Wby does it have
to be so complicated?  E.g. if you have to do something special for
method that touches an attribute without doing a setattr operation on
it, why not have the magic be inside that method rather than declare a
wrapper?  (The wrapper looks like it is much more expensive than
another way of flagging a change would be.)

What exactly is the point of collapsing multiple setattr() ops
together?  Just performance?  Or is there a semantic reason?  If just
performance, where is the time going that you're trying to save?

What's the use case for declaring a method as "touches an attribute
but that change should be ignored"?  (If it's only __init__, a
lighter-weight mechanism might be sufficient.)

--Guido van Rossum (home page: http://www.python.org/~guido/)