[Python-ideas] Empty set, Empty dict

[Philipp A.]

i honestly don’t see the problem here.

if people are too lazy to find a input method that works for them (Alt Gr,
compose key, copy&paste), they should just continue to type ASCII, and
leave the more elegant unicode variants for others.

this violates TSBOOWTDI, but as there’s also dict() next to {}, this should
neither be a problem.

i like scala’s way to allow both <- and ←, as well as => and ⇒, and so on.
∅ and λ seem like good ideas to me as un-redefinable empty set literal and
shorter/more elegant lambda. And “…” for “Ellipsis”.

there’s also ∀, ¬, ×, ∧,∨, ∩, ∪, ∈, ∉, ≠, ≡, ≤, and ≥, but i think those
are a bit much:

my_set = ∅
my_set ∪= other_set
my_set = map(λ e: e × 5, my_set ∩ third_set)
*∀* spam *∈* my_set:
    if spam *≡* None *∨* spam ≤ 8:
        print(spam *∉* allowed_values, *¬* spam)

vs.

my_set = ∅
my_set &= other_set
my_set = map(λ e: e * 5, my_set | third_set)
for spam in my_set:
    if spam is None or spam <= 8:
        print(spam not in allowed_values, not spam)

​


2014-06-22 14:29 GMT+02:00 Clint Hepner <clint.hepner at gmail.com>:

> There's one more, even more obvious (IMO) option for an empty set literal:
> U+2205, EMPTY SET. But that opens a whole other can of worms, namely
> expanding the grammar to allow Unicode characters outside of identifiers.
>
> On Jun 22, 2014, at 5:25 AM, "Philipp A." <flying-sheep at web.de> wrote:
>
> of course it’s ugly, but it’s also obvious that it had to be suggested,
> because it’s the only obvious idea.
>
> which leaves us with either a non-obvious idea or no empty set literal,
> which is a bit sad and inconsistent.
>
> if i’d develop a language from scratch, i’d possibly use the following
> empty literals:
>
> [] = list; () = tuple, {} = set
> [:] = ordered dict, (:) = named tuple, {:} = dict
>
> but that ship has sailed.
>
>
> 2014-06-10 18:39 GMT+02:00 Guido van Rossum <guido at python.org>:
>
>> No. Jeez. :-(
>>
>>
>> On Tue, Jun 10, 2014 at 9:25 AM, Ryan Gonzalez <rymg19 at gmail.com> wrote:
>>
>>> +1 for using {,}.
>>>
>>>
>>> On Tue, Jun 10, 2014 at 4:07 AM, Wichert Akkerman <wichert at wiggy.net>
>>> wrote:
>>>
>>>> Victor Stinner wrote:
>>>>
>>>> 2014-06-10 8:15 GMT+02:00 Neil Girdhar <mistersheik at gmail.com <https://mail.python.org/mailman/listinfo/python-ideas>>:
>>>>
>>>>
>>>>
>>>>
>>>> >* I've seen this proposed before, and I personally would love this, but my
>>>> *>* guess is that it breaks too much code for too little gain.
>>>> *>>* On Wednesday, May 21, 2014 12:33:30 PM UTC-4, Frédéric Legembre wrote:
>>>> *>>>>>>*    Now   |  Future  |
>>>> *>>* ----------------------------------------------------
>>>> *>>*    ()    |   ()     |  empty tuple  ( 1, 2, 3 )
>>>> *>>*    []    |   []     |  empty list   [ 1, 2, 3 ]
>>>> *>>*    set() |   {}     |  empty set    { 1, 2, 3 }
>>>> *>>*    {}    |   {:}    |  empty dict   { 1:a, 2:b, 3:c }
>>>> *
>>>>
>>>> Your guess is right. It will break all Python 2 and Python 3 in the world.
>>>>
>>>> Technically, set((1, 2)) is different than {1, 2}: the first creates a
>>>> tuple and loads the global name "set" (which can be replaced at
>>>> runtime!), whereas the later uses bytecode and only store values
>>>> (numbers 1 and 2).
>>>>
>>>> It would be nice to have a syntax for empty set, but {} is a no-no.
>>>>
>>>>
>>>> Perhaps {,} would be a possible spelling. For consistency you might
>>>> want to allow (,) to create an empty tuple as well; personally I would find
>>>> that more intuitive that (()).
>>>>
>>>> Wichert.
>>>>
>>>>
>>>>
>>>>
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>>>
>>>
>>>
>>> --
>>> Ryan
>>> If anybody ever asks me why I prefer C++ to C, my answer will be simple:
>>> "It's becauseslejfp23(@#Q*(E*EIdc-SEGFAULT. Wait, I don't think that was
>>> nul-terminated."
>>>
>>>
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>>>
>>
>>
>>
>> --
>> --Guido van Rossum (python.org/~guido)
>>
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>
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