[Python-Dev] Switch statement (original) (raw)

Guido van Rossum guido at python.org
Wed Jun 21 18:26:38 CEST 2006

On 6/21/06, Phillip J. Eby <pje at telecommunity.com> wrote:

At 03:38 AM 6/21/2006 -0500, Ka-Ping Yee wrote: >On Wed, 21 Jun 2006, Phillip J. Eby wrote: > > Well, EIBTI and all that: > > > > switch x: > > case == 1: foo(x) > > case in S: bar(x) > > > > It even lines up nicely. :) > >Hmm, this is rather nice. I can imagine possible use cases for > > switch x: > case > 3: foo(x) > case is y: spam(x) > case == z: eggs(x) > >An interesting use case for which this offers no corresponding >syntax is > > case instanceof ClassA: ham(x)

Actually, I was assuming that any other operator besides == and 'in' would be relegated to an if-elif chain in the default case, although it's almost possible to do that automatically, I suppose.

I've been thinking about generalization to other operators too, but decided that it would be a mistake. It would be quite clumsy to explain the exact semantics: if all operators are "==" or "in" an efficient hash table gets pre-constructed at function definition time, otherwise, um..., what exactly?

(Note how I've switched to the switch-for-efficiency camp, since it seems better to have clear semantics and a clear reason for the syntax to be different from if/elif chains.)

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

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