On 1/26/08, VanL <van.lindberg@gmail.com> wrote:
I like Raymond's suggestion (apparently adopted) that {1,2,3} is a frozenset literal. However, I also like the {{1,2,3}} syntax. So I would propose that {{}} become the literal for the *mutable* set, not the frozenset.
As Adam Atlas has already pointed out, {{}} already has a meaning in the newly proposed scheme. But that's not really the point that needs to be made. The typical response to this type of suggestion is to point out the obvious technical flaw, and that's a shame, because I don't think that's the real problem. You could have instead suggested, say, {|1, 2, 3|} as the new syntax for set literals. That fixes the technical flaw, but it still would have been, I believe, a bad idea. I don't understand the instinct people have that every concept needs to be generalized, that every non-uniformity in the language needs fixing. Normally the target is adding statements to lambdas, but today our bikeshed is the set literal syntax. There seems to be an underlying assumption to these posts that I find irritiating -- that the Python designers and developers would have added these features if only they were smart enough to be able to think up a syntax for them without assistance! Raymond Hettinger's frozenset literal proposal is solid. It recognizes that sets created from literal notation will typically not be mutated, that set({1,2,3}) is not a burdensome syntax in the off cases, and that literal frozensets admit a new and faster idiom for comparing a value against a small set of constants. The one flaw with his proposal was his prediction: On 1/24/08, Raymond Hettinger <python@rcn.com> wrote:
P.S. A small side-benefit is it may put an end for interminable requests for a {:} or {/} notation for empty sets. There's not much need for a literal for a empty frozenset (use "not s" instead).
It turned out to only take about two days. Greg F