[Python-Dev] Any grammar experts?

[Antoine Pitrou]

On Sun, 25 Jan 2015 14:59:42 -0800
Guido van Rossum <guido at python.org> wrote:
> On Sun, Jan 25, 2015 at 7:32 AM, Georg Brandl <g.brandl at gmx.net> wrote:
> 
> > On 01/25/2015 04:08 PM, Antoine Pitrou wrote:
> > > On Sat, 24 Jan 2015 21:10:51 -0500
> > > Neil Girdhar <mistersheik at gmail.com> wrote:
> > >> To finish PEP 448, I need to update the grammar for syntax such as
> > >>
> > >> {**x for x in it}
> > >
> > > Is this seriously allowed by the PEP? What does it mean exactly?
> >
> > It appears to go a bit far.  Especially since you also would have to allow
> >
> > {*x for x in it}
> >
> > which is a set comprehension, while the other is a dict comprehension :)
> >
> 
> That distinction doesn't bother me -- you might as well claim it's
> confusing that f(*x) passes positional args from x while f(**x) passes
> keyword args.
> 
> And the varargs set comprehension is similar to the varargs list
> comprehension:
> 
> [*x for x in it]
> 
> If `it` were a list of three items, this would be the same as
> 
> [*it[0], *it[1], *it[2]]

I find all this unreadable and difficult to understand.

Regards

Antoine.