On Fri, Oct 23, 2020 at 12:31 AM Eric V. Smith <e...@trueblade.com> wrote:
>
> On 10/22/2020 8:29 AM, Chris Angelico wrote:
> > On Thu, Oct 22, 2020 at 8:22 PM Steven D'Aprano <st...@pearwood.info> wrote:
> >> Another problem is that using only a literal/display form as a target
> >> means you can't pre-assemble a pattern and apply it later:
> >>
> >> # Match only the given domain.
> >> domain = get_wanted_domain()
> >> pattern = 'email: {name}@%s' % domain
> >> # ... now what?
> > Right, and you can't do that with f-strings on the RHS either. The
> > specific thing you're asking about could easily be implemented as a
> > feature of the minilanguage itself, but I'm not sure it'd actually be
> > needed. Building patterns for future parsing is simply not the job of
> > this feature - use a regex if you need that.
>
> In the case of f-strings, the fallback is str.format(), which uses the
> exact same format specifiers. What's the equivalent when you need
> dynamic 'f-string assignment targets'?
>
Good question, but whatever it is, it can be part of the same
proposal. A standard library function that does the same kind of thing
but returns a dictionary would be useful, even if it isn't as
important. Pike has sscanf (compiler feature that assigns directly to
things) and array_sscanf (returns a sequential collection of matched
items), and Python could do the same kind of thing. Returning a dict
would be FAR less convenient for the most common cases, but as you
say, it'd be the fallback for when you need dynamic parsing.
ChrisA
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