[Python-Dev] PEP 435 -- Adding an Enum type to the Python standard library

[Serhiy Storchaka]

26.04.13 18:50, Larry Hastings написав(ла):
> On 04/26/2013 12:34 AM, Greg Ewing wrote:
>> Or if, as Guido says, the only sensible things to use
>> as enum values are ints and strings, just leave anything
>> alone that isn't one of those.
>
> The standard Java documentation on enums:
>
>     http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
>
> has an example enum of a "Planet", a small record type containing mass
> and radius--each of which are floats.  I don't know whether or not it
> constitutes good programming, but I'd be crestfallen if Java enums were
> more expressive than Python enums ;-)

This example requires more than features discussed here. It requires an 
enum constructor.

class Planet(Enum):
     MERCURY = Planet(3.303e+23, 2.4397e6)
     VENUS   = Planet(4.869e+24, 6.0518e6)
     EARTH   = Planet(5.976e+24, 6.37814e6)
     MARS    = Planet(6.421e+23, 3.3972e6)
     JUPITER = Planet(1.9e+27,   7.1492e7)
     SATURN  = Planet(5.688e+26, 6.0268e7)
     URANUS  = Planet(8.686e+25, 2.5559e7)
     NEPTUNE = Planet(1.024e+26, 2.4746e7)

     def __init__(self, mass, radius):
         self.mass = mass     # in kilograms
         self.radius = radius # in meters

     @property
     def surfaceGravity(self):
         # universal gravitational constant  (m3 kg-1 s-2)
         G = 6.67300E-11
         return G * self.mass / (self.radius * self.radius)

     def surfaceWeight(self, otherMass):
         return otherMass * self.surfaceGravity

This can't work because the name Planet in the class definition is not 
defined.