On Fri, Sep 18, 2020 at 4:56 AM Steven D'Aprano <st...@pearwood.info> wrote:

> But that's a *separate problem*. Regexes can't assign directly either.
> And we wouldn't want them to! (It's okay for a regex to have it's own
> internal namespace, like named groups, but it shouldn't leak out into
> the locals or globals.)
>
> Extracting data from a string, like scanf, regexes, sed, awk, SNOBOL etc
> sounds like a big win. Assignment should be a separate problem.
>
> And at last I think I have thought of a use of dict unpacking I like. If
> our scanf(pattern, target) function returns a dict of {name: value}
> pairs, how do we apply it to locals?
>
>     target [, names] = **scanf(pattern, target)
>
> where dict assignment matches assignment targets on the left with keys
> in the dict. Acceptable target names are simple identifiers, dotted
> names and subscripts:
>
>
>     spam, eggs.fried, cheese[0] = **{'cheese[0]': 3,
>                                      'spam': 1,
>                                      'eggs.fried': 2}
>
>
> would do the obvious assignments. (I could live without the dotted names
> and subscripts, if people don't like the additional complexity.)
>
> Targets missing a key:value, or keys missing a target, would raise an
> exception.
>
> The bottom line here is that separation of concerns is a principle we
> should follow. Text scanning and assignment are two distinct problems
> and we should keep them distinct. This will allow us to pre-process the
> pattern we want to match, and post-process the results of the scan, e.g.
>
>     spam, eggs, cheese = **(defaults | scanf(pattern, string))
>
>
> We could have multiple scanners too, anything that returned a dict of
> target names and values. We wouldn't need to build the scanner into the
> interpreter, only the assignment syntax. The scanner itself is just a
> function.
>

 +1. Dict unpacking would be great, I'm not sure why we don't have it
already. And I agree with the separation of concerns. If we had dict
unpacking we could already do this kind of thing with named capture groups
and groupdict.
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