On Tue, Feb 11, 2003 at 02:33:45PM +0100, Alex Martelli wrote:
>
> def setdefault(adict, akey, ?avalue):
> if akey not in adict:
> adict[akey] = evaluate_now(avalue)
> return adict[akey]
>
> to be called as, e.g.
>
> setdefault(mydict, 'goo', ?makeavalue(x))
>
> this would use ? for both formal and actual arguments to
> mean lazy evaluation, and a new builtin to force the time
> of evaluation. Other choices are, of course, possible.
+0.5
when nobody is looking I smirk at the fact that tcl has a feature python
doesn't ;-) (well, not really... it could be argued our lambda does the same
thing better)
Instead of a new builtin, I think the "lazy evaluation block" should be an
object; you can then call a method, in your example avalue.eval()
What happens if you don't add the ? to the call? setdefault(mydict, 'foo', v)
IMHO it would still build a "lazy evaluation block" but somehow "already
evaluated".
One more important bit: what happens if you call .eval() multiple times? Do
each one result in a new evaluation, or is the result cached internally? I
can see use cases for both. Perhaps ruling that each .eval() re-evaluates
the block works - then if you want to avoid it, just assign the result to a
local variable (explicit).
OTOH, off the top of my head I can't think of another valid use case for
this whole feature other than setdefault.
[]s,
|alo
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