"Phillip J. Eby" <[EMAIL PROTECTED]> wrote:
> At 06:56 PM 6/18/2006 -0700, Josiah Carlson wrote:
> >The non-fast version couldn't actually work if it referenced any names,
> >given current Python semantics for arbitrary name binding replacements.
>
> Actually, one could consider "case" expressions to be computed at function
> definition time, the way function defaults are. That would solve the
> problem of symbolic constants, or indeed any sort of expressions.
Using if/elif/else optimization precludes any non-literal constants, so
we would necessarily have to go with a switch/case for this semantic. It
seems as though it would work well, and wouldn't be fraught with
any of the gotchas that catch users like:
def fcn(..., dflt={}, dflt2=[]):
...
> An alternate possibility would be to have them computed at first use and
> cached thereafter.
>
> Either way would work, and both would allow multiple versions of the same
> switch statement to be spun off as closures without losing their "constant"
> nature or expressiveness. It's just a question of which one is easier to
> explain. Python already has both types of one-time initialization:
> function defaults are computed at definition time, and modules are only
> loaded once, the first time you import them.
I would go with the former rather than the latter, if only for
flexibility.
- Josiah
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