[Python-Dev] constant/enum type in stdlib

[Ron Adam]

Oops..  x**2 should have been 2**x below.


On 11/23/2010 03:03 PM, Ron Adam wrote:
>
>
> On 11/23/2010 12:07 PM, Antoine Pitrou wrote:
>> Le mardi 23 novembre 2010 à 12:50 -0500, Isaac Morland a écrit :
>>> Each enumeration is a type (well, OK, not in every language, presumably,
>>> but certainly in many languages). The word "basic" is more important than
>>> "types" in my sentence - the point is that an enumeration capability is a
>>> very common one in a type system, and is very general, not specific to any
>>> particular application.
>>
>> Python already has an enumeration capability. It's called range().
>> There's nothing else that C enums have. AFAICT, neither do enums in
>> other mainstream languages (assuming they even exist; I don't remember
>> Perl, PHP or Javascript having anything like that, but perhaps I'm
>> mistaken).
>
>
> Aren't we forgetting enumerate?
>
>  >>> colors = 'BLACK BROWN RED ORANGE YELLOW GREEN BLUE VIOLET GREY WHITE'
>
>  >>> dict(e for e in enumerate(colors.split()))
> {0: 'BLACK', 1: 'BROWN', 2: 'RED', 3: 'ORANGE', 4: 'YELLOW', 5: 'GREEN', 6:
> 'BLUE', 7: 'VIOLET', 8: 'GREY', 9: 'WHITE'}
>
>  >>> dict((f, n) for (n, f) in enumerate(colors.split()))
> {'BLUE': 6, 'BROWN': 1, 'GREY': 8, 'YELLOW': 4, 'GREEN': 5, 'VIOLET': 7,
> 'ORANGE': 3, 'BLACK': 0, 'WHITE': 9, 'RED': 2}
>
>
> Most other languages that use numbered constants number them by base n^2.
>
>  >>> [x**2 for x in range(10)]
> [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]


 >>> [2**x for x in range(10)]
[1, 2, 4, 8, 16, 32, 64, 128, 256, 512]


> Binary flags have the advantage of saving memory because you can assign
> more than one to a single integer. Another advantage is other languages use
> them so it can make it easier interface with them. There also may be some
> performance advantages as well since you can test for multiple flags with a
> single comparison.
>
> Sets of strings can also work when you don't need to associate a numeric
> value to the constant. ie... the constant is the value. In this case the
> set supplies the api.
>
> Cheers,
> Ron
>
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