Well, I've just waded through this discussion. This all feels to me like a special case of "wanting a constant for bytecode". What is we had a "freeze" operator, eg: |foo| which would produce a frozen version of foo. I'm liking the vertical bars myself, I think because it feels vaguely slightly analogous to "absolute value". So (assuming we can squeeze it into the expression syntax): |{1,2,3}| always makes a direct frozen set on the same basis that: x in {1,2,3} directly makes a frozenset by expression inspection. Then Paired with a __freeze__ dunder method, this applies to any type, not just sets. (Where appropriate of course.) So: |{1,2,3}| frozen set |[1,2,3]| tuple! |any-iterable| tuple! |{1:2, 3:4}| frozen dict Ths saves us (a) inventing a special syntax for frozen sets and (b) gateways to freezing many things, starting with the obvious above, via the __freeze__ dunder method. This feels more general and less bikeshedable. My main question is: is the syntax unambiguous? Cheers, Cameron Simpson <cs@cskk.id.au>