On Sat, 9 Jan 2021 12:17:32 +0000 Paul Moore <[email protected]> wrote:
> On Sat, 9 Jan 2021 at 10:52, Paul Sokolovsky <[email protected]> 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 -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/[email protected]/message/BZOIB3NTXICLJYCIE6GSMUPWVI4DG3UG/ Code of Conduct: http://python.org/psf/codeofconduct/