[Python-ideas] Possible method of distinguishing between set-literals, dict-literals, and odict-literals

[Terry Reedy]

MRAB wrote:
> Ron Adam wrote:
>>
>>
>> Ben Finney wrote:
>>> Carl Johnson
>>> <cmjohnson.mailinglist at gmail.com> writes:
>>>
>>>> we could introduce an empty set-literal and an odict-literal, and add
>>>> a more explicit form to replace the existing set literal.
>>>
>>> What do you mean by “more explicit”? The existing set literal syntax
>>> is quite explicit.
>>>
>>>> s{} could be the empty set, o{} could be an empty odict, and we could
>>>> leave {} alone as the form for dicts. So, an odict literal would look
>>>> like o{'a':'1', 'b':'2', 'c':'3'} instead of OrderedDict([('a', '1'),
>>>> ('b', '2'), ('c', '3')]). And the set {'a', 'c', 'b'} could
>>>> (optionally?) have a little s{'a', 'c', 'b'} to make it more explicit
>>>> that this is a set, not a dict.
>>>
>>> I don't think that word “explicit” means what you think it means.
>>
>> I think Carl is thinking that it is more concise and easier to read.
>>
>> When you read OrderedDict([('a', '1'),('b', '2'), ('c', '3')]),  your 
>> mind is parsing  *Ordered Dictionary from list of these three tuples*.
>>
>> Whebn you read *o{'a':'1', 'b':'2', 'c':'3'}*, your mind does not have 
>> the extra noise of converting the argument list of the constructor.
>>
> How about ['a':'1', 'b':'2', 'c':'3']?
> 
>>
>> I think it really depends on how often ordered dictionaries literals 
>> will be used weather or not it is worth doing.  It also uses about 30% 
>> to 50% less keystrokes.
>>
> Ideally we would have [...] for ordered and {...} for unordered, with
> ':' if it's keyed:
> 
>     []  ordered,   value      (list)
>     [:] ordered,   key+value  (odict)
>     {}  unordered, value      (set)
>     {:} unordered, key+value  (dict)
> 
> It's too late to change that in Python 3.x, so it would have to be:
> 
>     []  ordered,   value      (list)
>     [:] ordered,   key+value  (odict)
>     {,} unordered, value      (set)
>     {}  unordered, key+value  (dict)
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