[Python-Dev] Enumeration item arguments?

[Philip Jenvey]

On Apr 29, 2013, at 3:25 PM, Eli Bendersky wrote:

> On Mon, Apr 29, 2013 at 2:59 PM, Ethan Furman <ethan at stoneleaf.us> wrote:
> In the Planet example we saw the possibility of specifying arguments to enum item __init__:
> 
> class Planet(Enum):
>     MERCURY = (3.303e+23, 2.4397e6)
>     VENUS   = (4.869e+24, 6.0518e6)
>     EARTH   = (5.976e+24, 6.37814e6)
>     MARS    = (6.421e+23, 3.3972e6)
>     JUPITER = (1.9e+27,   7.1492e7)
>     SATURN  = (5.688e+26, 6.0268e7)
>     URANUS  = (8.686e+25, 2.5559e7)
>     NEPTUNE = (1.024e+26, 2.4746e7)
> 
>     def __init__(self, mass, radius):
>         self.mass = mass       # in kilograms
>         self.radius = radius   # in meters
> 
> Do we want to support this?
> 
> I'm -1, and this is yet another bad sign of conflating enums with classes. If planets want to have attributes and behaviors, let them be normal classes. If they want a PlanetId *enum member*, that's OK, but there's no need to intermix the two.

You may be right about the Planet example, but I wouldn't go that far. Additional metadata on Enum instances can be a handy feature in some cases, like documentation, e.g.:

class Protocol(Enum):

 HOPOPT = 0, "IPv6 Hop-by-Hop Option"
 ICMP = 1, "Internet Control Message"
 IGMP = 2, "Internet Group Management"

 @property
 def value(self):
     return self._value[0]

 @property
 def description(self):
   return self._value[1]


--
Philip Jenvey