[Python-Dev] Re: PEP 318: Decorators last before colon

[David Eppstein]

In article <3AA96ED4-876E-11D8-A42F-0003934AD54A at chello.se>,
 Simon Percivall <s.percivall at chello.se> wrote:

> On 2004-04-06, at 01.24, David Eppstein wrote:
> >
> > Ok, then how about
> >     <decorator>
> >     def ...
> > ?
> >
> > '<' can't start an expression or statement currently, can it?
> 
> Yeah. I think that would look better. On the other hand ...
> 
> On 2004-03-31, at 17.42, Guido van Rossum wrote:
> > Why does <...> look better than [...]?  To me, <...> just reminds me
> > of XML, which is totally the wrong association.
> >
> > There are several parsing problems with <...>: the lexer doesn't see <
> > and > as matched brackets, so you won't be able to break lines without
> > using a backslash, and the closing > is ambiguous -- it might be a
> > comparison operator.

Well, Mike Pall's long message "The Need for a Declarative Syntax" 
convinced me that some kind of bracketed prefix is the best location for 
these things, but I still don't like [...] because it already has a 
(useless) meaning, so declarators would pass silently in old Pythons.
And the same objection applies to all other existing brackets.
So, angle brackets seem like the cleanest remaining choice.

Re the lexer, I don't see this as a big problem as long as multiple 
declarators can be handled by multiple <...> pairs.  Re the ambiguity, I 
think comparisons shouldn't normally appear in declarators, so it's ok 
if they have to be parenthesized.

-- 
David Eppstein                      http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science