ways to declare empty set variable

[Steve Holden]

Boris Borcic wrote:
> bearophileHUGS at lycos.com wrote:
>> ...Missing that, I think dict() and set() and
>> tuple() and list() look better than using {} for the empty dict and
>> {/} for the empty set and () for empty tuple (or {} for the empty dict
>> and set() for the empty set).
> 
> The problem I have with them is in no way the looks, it is that they are not 
> strictly equivalent as they imply dictionary lookups. Which shows in performance, eg
> 
>  >>> import timeit
>  >>> timeit.Timer('[]').timeit()
> 0.22358344426456436
>  >>> timeit.Timer('list()').timeit()
> 0.54574505977715049
>  >>> timeit.Timer('{}').timeit()
> 0.21328632549668214
>  >>> timeit.Timer('dict()').timeit()
> 0.50557906102591232
> 
But this is "performance" in the abstract. It's hardly going to matter 
if you use it once in the initialization of your program, but if it 
occurs deep inside a quadruply-nested loop that is executed 10^12 times 
it may have an impact on performance.

Before you have any code is exactly the *wrong* time to be considering 
performance.

regards
  Steve
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