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Hmm, I intended to have s1.refresh() return a new object for use in s2 while leaving s1 alone (being immutable and all). Now, I wonder if that was the right thing to do. The answer lies in use cases for algorithms that need sets of sets. If anyone knows off the top of their head that would be great; otherwise, I seem to remember that some of that business was found in compiler algorithms and graph packages.

Let's call YAGNI on this one.

Furthermore, what if I create a BIG set like this: s = ImmutableSet( range(2**x) ) Now, not only do I use lots of memory for s, I ALSO keep around lots of memory to preserve a temporary list which I never wanted to keep anyhow! -- Michael Chermside