On Tue, Feb 17, 2009 at 3:01 PM, Steven D'Aprano <steve@pearwood.info> wrote:

I think that test_and_add is naturally two operations, not one, and forcing it to be one operation will just lead to confusion.

There is one scenario where testing membership and adding a new member *is* a single operation: multiple threads.

That's a good reason to *not* support a test/change operation in regular sets as it may lead people to think (falsely) that it provide some kind of concurrency protection.

--- Bruce