How to define custom properties in enumeration in Python (Javascript-like)

Question

In JavaScript we can do this:

var Color = {
    YELLOW: { value: 1, displayString: "Yellow" },
    GREEN: { value: 2, displayString: "Green" },
}

So I can call:

Color.YELLOW.displayString

In Java we can do this:

public enum Color {

    YELLOW (1, "Yellow"),
    GREEN (2, "Green"),

    private Color(String value, int displayString){
        this.value = value;
        this.displayString = displayString;
    }

    private final int value;
    private final String displayString;

    public String getValue() {return value;}
    public String getDisplayString() {return displayString;}
}

So I can call:

Color.YELLOW.getDisplayString()

After much research I haven't found a clean way to do this in Python using the built-in Enum module. How can I do this?

Thanks

The javascript is an object more closely related to a HashMap in Java. There is a Dictionary in python that might serve your purposes. — scrappedcola, Feb 23 '16 at 02:37

Thomas Lotze · Accepted Answer · 2016-02-23T08:05:22.220

34

There are two concepts involved here: enumerations and attribute-style access to object members that can be initialised inline. For the latter, you'll need some kind of custom class, but since you want something very straightforward, a namedtuple is sufficient for that. So, combining namedtuple and enum, this could be a solution:

from enum import Enum
from collections import namedtuple

Color = namedtuple('Color', ['value', 'displayString'])

class Colors(Enum):

    @property
    def displayString(self):
        return self.value.displayString

    yellow = Color(1, 'Yellow')
    green = Color(2, 'Green')

print(Colors.yellow.displayString)

edited Feb 23 '16 at 08:05

answered Feb 23 '16 at 02:43

Thomas Lotze

5,153
1
16
16

Thank you very much that is what I needed! Combined with the use of @property annotations we can access underlying values directly like this: Colors.yellow.displayString – olivierr91 Feb 23 '16 at 04:09
Thank you for pointing this out, I've edited the answer to demonstrate it. – Thomas Lotze Feb 23 '16 at 08:06
1

how to get an enum object by value? Is it working here! – Biswa Bandhu Bhandary Sep 10 '21 at 02:54
i think yellow.value does not work here. Enum can be removed and value may be implemented with @property as a workaround. Then it is not enum anymore. – isilpekel Jan 03 '23 at 10:17

Arany · Answer 2 · 2016-11-23T07:22:39.637

Here is another approach, that is the code from: https://github.com/hzdg/django-enumfields

import enum
import inspect

class ColorEnumMeta(enum.EnumMeta):
    def __new__(mcs, name, bases, attrs):
        DisplayStrings = attrs.get('DisplayStrings')

        if DisplayStrings is not None and inspect.isclass(DisplayStrings):
            del attrs['DisplayStrings']
            if hasattr(attrs, '_member_names'):
                attrs._member_names.remove('DisplayStrings')

        obj = super().__new__(mcs, name, bases, attrs)
        for m in obj:
            m.display_string = getattr(DisplayStrings, m.name, None)

        return obj

class Color(enum.Enum, metaclass=ColorEnumMeta):
    yellow = 1
    green = 2

    class DisplayStrings:
        yellow = 'Yellow'
        green = 'Green'

print(Color.yellow.display_string)  # 'Yellow'

or something that is based on this code, but a bit shorter:

import enum

class ColorEnumMeta(enum.EnumMeta):
    def __new__(mcs, name, bases, attrs):
        obj = super().__new__(mcs, name, bases, attrs)
        obj._value2member_map_ = {}
        for m in obj:
            value, display_string = m.value
            m._value_ = value
            m.display_string = display_string
            obj._value2member_map_[value] = m

        return obj

class Color(enum.Enum, metaclass=ColorEnumMeta):
    yellow = 1, 'Yellow'
    green = 2, 'Green'

print(Color.yellow.display_string)  # 'Yellow'

score -5 · Answer 3 · answered Feb 23 '16 at 02:44

-5

You can use a dictionary in python:

Color = { 
    'YELLOW': { 'value': 1, 'displayString': "Yellow" },
    'GREEN': { 'value': 2, 'displayString': "Green" }
}
Color['YELLOW']['displayString']

answered Feb 23 '16 at 02:44

scrappedcola

10,423
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43

score -6 · Answer 4 · answered Feb 23 '16 at 02:47

You should normally never include literals like this in your code. The content should come from a file or database. But you can see how to build it up

>>> from collections import namedtuple
>>> Color = namedtuple("color", "YELLOW,GREEN")(
        namedtuple("yellow", "value,display_string")(1, "yellow"),
        namedtuple("green", "value,display_string")(2, "green"))
>>> Color.YELLOW.display_string
'yellow'

This also works for older Pythons that don't support enum

How to define custom properties in enumeration in Python (Javascript-like)

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