[Python-ideas] Draft PEP on string interpolation

[Guido van Rossum]

On Sat, Aug 22, 2015 at 3:09 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 22 August 2015 at 15:52, Mike Miller <python-ideas at mgmiller.net> wrote:
> > Hi,
> >
> > I'm not sure that's the case any more, after reading the threads here
> this
> > week there are numerous difficulties with trying to reconcile both use
> > cases, and didn't get the feeling anyone has an elegant solution to them.
> >
> > We could implement f'' and (i'', aka t'') using either syntax of course,
> > parsing variables from the string, but choosing translation with
> > str.format() seems to cause several more issues than (string.Template()
> and
> > a bit of inconsistency does).
> >
> > Which syntax would you rather have for translation?  (Knowing that you
> might
> > give a different answer for standard interpolation.)
>
> I just pushed a major rewrite of PEP 501 based on the discussions
> since the initial version of that and PEP 498 went online:
> https://www.python.org/dev/peps/pep-0501/
>
> It switches to using a magic method and explicitly named interpolator
> in interpolation expressions, with "!str" being the interpolator
> reference for default string formatting. From a motivation
> perspective, while i18n remains a consideration, more easily
> addressing the risk of code injection attacks against naive use of
> string interpolation when generating database queries, shell commands
> or HTML pages now provides a stronger motivation making the
> interpolation semantics extensible.
>
> Writing a custom interpolator (including for i18n) becomes as simple as
> doing:
>
>     @interpolator
>     def my_interpolator(raw_template, parsed_fields, field_values):
>         ...
>
> While using it then looks like:
>
>     result = !my_interpolator "This has $values $mixed into it"
>
> (Similar to yield, it is proposed that interpolation expressions would
> require parentheses when embedded inside a larger expression)
>

1. That's an entirely different proposal, you're just reusing the PEP
number.

2.  Have I died and gone to Perl?

-- 
--Guido van Rossum (python.org/~guido)
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