On Sun, 8 Jan 2023 at 08:32, Stephen J. Turnbull
<stephenjturnb...@gmail.com> wrote:
>
> Steven D'Aprano writes:
>
> > On Sat, Jan 07, 2023 at 10:48:48AM -0800, Peter Ludemann wrote:
> > > You can get almost the same result using pattern matching. For example,
> your
> > > "foo:bar;baz".partition(":", ";")
> > > can be done by a well-known matching idiom:
> > > re.match(r'([^:]*):([^;]*);(.*)', 'foo:bar;baz').groups()
>
> > I think that the regex solution is also wrong because it requires you
> > to know *exactly* what order the separators are found in the source
> > string.
>
> But that's characteristic of many examples. In "structured" mail
> headers like Content-Type, you want the separators to come in the
> order ':', '=', ';'. In a URI scheme with an authority component, you
> want them in the order '@', ':'.
+1 (while also recognising the caveats you mention subsequently)
> Except that you don't, in both those
> examples. In Content-Type, the '=' is optional, and there may be
> multiple ';'. In authority, the existing ':' is optional, and there's
> an optional ':' to separate password from username before the '@'.
Trying to avoid the usual discussions about permissive parsing /
supporting various implementations in-the-wild: long-term, the least
ambiguous and most computationally-efficient environment would
probably want to reduce special cases like that? (both in-data and
in-code)
> user, _, domain = "example.com".partition('@')
>
> does the wrong thing!
Yep - it's important to choose partition arguments (I'm
mostly-resisting the temptation to call them a 'pattern') that are
appropriate for the input.
Structural pattern matching _seems_ like it could correspond here, in
terms of selecting appropriate arguments -- but it is, as I understand
it, limited to at-most-one wildcard pattern per match (by sensible
design).
> I would prefer "one bite per call" partition
> to a partition at multiple points.
That does seem clearer - and clearer is, generally, probably better.
I suppose an analysis (that I don't have the ability to perform
easily) could be to determine how many regular expression codesites
could be migrated compatibly and beneficially by using
multiple-partition-arguments.
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