Can named arguments be used with Python enums?

Question

Example:

class Planet(Enum):

    MERCURY = (mass: 3.303e+23, radius: 2.4397e6)

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

Ref: https://docs.python.org/3/library/enum.html#planet

Why do I want to do this? If there are a few primitive types (int, bool) in the constructor list, it would be nice to used named arguments.

Answer 1

While you can't use named arguments the way you describe with enums, you can get a similar effect with a namedtuple mixin:

from collections import namedtuple
from enum import Enum

Body = namedtuple("Body", ["mass", "radius"])

class Planet(Body, Enum):

    MERCURY = Body(mass=3.303e+23, radius=2.4397e6)
    VENUS   = Body(mass=4.869e+24, radius=6.0518e6)
    EARTH   = Body(mass=5.976e+24, radius=3.3972e6)
    # ... etc.

... which to my mind is cleaner, since you don't have to write an __init__ method.

Example use:

>>> Planet.MERCURY
<Planet.MERCURY: Body(mass=3.303e+23, radius=2439700.0)>
>>> Planet.EARTH.mass
5.976e+24
>>> Planet.VENUS.radius
6051800.0

Note that, as per the docs, "mix-in types must appear before Enum itself in the sequence of bases".