[Python-ideas] frozenset literals

[Joshua Landau]

On 13 February 2013 21:02, <random832 at fastmail.us> wrote:

> On Sat, Feb 2, 2013, at 9:20, Steven D'Aprano wrote:
> > Unfortunately the proposal to use f{ ... } for frozen sets cannot work
> > within the constraints of Python's lexer:
> >
> > http://mail.python.org/pipermail/python-3000/2008-January/011838.html
> >
> > Unfortunately we're running out of useful, easy to enter symbols for
> > literals. Until such time (Python4000 perhaps, or more likely Python5000)
> > as we can use a rich set of Unicode literals, I don't think there is any
> > clear way to have a frozenset literal.
>
> I was going to post about not being sure what the objection is (if it's
> multiple tokens, let it be multiple tokens - the contents are multiple
> tokens anyway - and saying it would block a future syntax extension
> doesn't seem like a reasonable objection to a proposed syntax
> extension), but I had a new idea so I'll post that instead:
>
> { as frozenset { ... } }
>
> The sequence "{ as" can't occur (to my knowledge) anywhere now. So, the
> thing after it is a keyword in that context (and only that context,
> otherwise "frozenset" remains an identifier naming an ordinary builtin)
> and specifies what kind of literal the following sequence is. You could
> also extend it to alternate forms for some other builtin types - for
> example { as bytes [1, 2, 3, 4, 5] } instead of b"\x1\x2\x3\x4\x5".
> Or... { as set { } }


I'm really not sure I like this idea, but surely:

LITERAL as KEYWORD
{ ... } as frozenset
[1, 2, 3, 4, 5] as bytes
{} as set

would work better.

However, I'm not happy on the idea that an identifier can be a keyword in
another context.
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