On Mon, Jul 5, 2021 at 5:05 PM Chris Angelico <ros...@gmail.com> wrote:
> On Tue, Jul 6, 2021 at 9:39 AM Greg Ewing <greg.ew...@canterbury.ac.nz>
> wrote:
> >
> > On 6/07/21 9:56 am, Jim Baker wrote:
> > >
> > > d = deferred_tag"Some expr: {:(x*2)}"
> > >
> > > All that is happening here is that this being wrapped in a lambda,
> which
> > > captures any scope lexically as usual.
> >
> > Is there reason to think this will be a common enough requirement
> > to justify having an abbreviated syntax for a parameterless lambda
> > that's only available in template expressions?
> >
>
> If it's just being wrapped in a lambda function, probably nothing, but
> I think that that would be *very* surprising behaviour. People will
> expect that the expressions' values will be collected at the point you
> hit the interpolated string, not later when it gets used.
>
It would be surprising indeed if this was the *default* behavior, that's
why you have to specially mark it using {:...} in Jim's proposal.
IIUC the idea is that the entire template becomes effectively a lambda.
It's useful if the evaluation is relatively expensive and may never be
needed, e.g. for logging at a level that is off in production. We can
debate whether it's better to mark individual substitutions with something
like {:...} or whether we should mark the template as a whole (obviously
the marking must be understandable by the parser).
--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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