On Sat, 9 Jan 2021 12:17:32 +0000
Paul Moore <p.f.mo...@gmail.com> wrote:
> On Sat, 9 Jan 2021 at 10:52, Paul Sokolovsky <pmis...@gmail.com> wrote:
> > > case {"host" as host, "port" as port}:
> >
> > There're 2 obvious problems with it:
> >
> > a) In Python, {} with things inside it, but no ":" inside it, is a set,
> > set.
> > b) Everywhere else in Python, thing on the left of "as" gets into
> > thing on the right of "as", behold:
> >
> > import foo as bar # original module "foo" gets into "bar".
> > with Cls(a, b) as c: # original expression "Cls(a, b)" gets into "c"
> >
> > Then based on the existing Python syntax, the meaning of '{"host" as
> > host, "port" as port}' is: a set, whose contained, constant in this
> > case, values "host" and "port" get captured as variables host and port.
> > In pattern matching context (with 'case' in front), it means: match
> > using a set, check for presence on constant "host" and "port" elements,
> > and capture those constants to variables host and port (that
> > capturing doesn't make much sense, yeah. And yet syntax tells just
> > that. You propose to assign to it completely different meaning.).
>
> This analysis nicely captures my reservations with the proposal here.
> It claims to be addressing the problems with PEP 634, where the syntax
> proposed there is specialised to matching, but it then proceeds to
> introduce another syntax, which is *also* unlike existing usage, just
> in different ways.
Introducing a new syntax is not a problem, it's the solution. The
problem with PEP 634 is precisely that it reuses existing syntax and
gives it a different meaning, thereby producing confusion.
It's erroneous to claim that `{"host" as host, "port" as port}` is a
set. It's currently invalid syntax due to the `as`:
>>> {"host" as host, "port" as port}
File "<stdin>", line 1
{"host" as host, "port" as port}
^
SyntaxError: invalid syntax
So, opposing Nick's proposal on the basis that it "looks like a set" is
just like opposing set literals on the basis they they "look like a
dict".
Regards
Antoine.
_______________________________________________
Python-Dev mailing list -- python-dev@python.org
To unsubscribe send an email to python-dev-le...@python.org
https://mail.python.org/mailman3/lists/python-dev.python.org/
Message archived at
https://mail.python.org/archives/list/python-dev@python.org/message/BZOIB3NTXICLJYCIE6GSMUPWVI4DG3UG/
Code of Conduct: http://python.org/psf/codeofconduct/
