[Python-ideas] frozenset literals

[MRAB]

On 2013-02-02 18:46, Hua Lu wrote:
> On Sat, Feb 2, 2013 at 12:30 PM, MRAB <python at mrabarnett.plus.com> wrote:
>> On 2013-02-02 14:28, Antoine Pitrou wrote:
>>> On Sun, 03 Feb 2013 01:20:38 +1100
>>> Steven D'Aprano <steve at pearwood.info> 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'm not sure what the point is. frozensets are too rarely used to
>>> deserve a literal notation.
>>>
>> Does it need a special notation as such?
>>
>> Wouldn't an alternative be to support "frozenset(...)" where "..." is
>> parseable by ast.literal_eval()?
>>
>> The same thing could be done with some other built-in classes.
>>
> Perhaps, but we'd have to be careful with how we introduce those symbols:
>
> http://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html
>
> You could possibly not allow attribute access but permit those
> symbols... is there an exploit possible with that much filtering?
>
I'm talking about hard-coding "frozenset(...)" and a few other built-in
classes to return the appropriate object, so, for example, "set([0, 1,
2])" would be the same as "{0, 1, 2}".