Getting enum object from string when enum values are tuples?

Question

I have Enum of the form

class ItemType(Enum):
    ITEM1 = ('Desc1', AnotherEnum.ONE)
    ITEM2 = ('Desc2', AnotherEnum.TWO)

and I am trying to instantiate an object of the type ItemType from a JSON string.

For example I would like to get the ItemType that logically represents the string 'Desc1'. If the enum values were of the form ITEM1 = 'Desc1' I could simple do ItemType('Desc1'). But in the current form I am not sure how I could achieve the lookup method.

Is there a way to do this?

Use another enum called Desc, then you can do ItemType(Desc('Desc1')) — smac89
– smac89, Commented Dec 22, 2017 at 0:18
@smac89 Can you turn that into an answer? I'd like to see the full example. — Thijs van Dien
– Thijs van Dien, Commented Dec 22, 2017 at 1:18

Thijs van Dien · Accepted Answer · 2020-10-10 04:44:28Z

An Enum is just a class, so how about an alternate constructor? It's the most explicit.

class ItemType(Enum):
    ITEM1 = ('Desc1', AnotherEnum.ONE)
    ITEM2 = ('Desc2', AnotherEnum.TWO)
    
    @classmethod
    def from_description(cls, description):
        for item in cls:
            if item.value[0] == description:
                return item
        raise ValueError("%r is not a valid %s description" % (description, cls.__name__))

You can then do ItemType.from_description('Desc1').

Alternatively, if you want ItemType('Desc1') to just work, as of Python 3.6 you can implement _missing_:

class ItemType(Enum):
    ITEM1 = ('Desc1', AnotherEnum.ONE)
    ITEM2 = ('Desc2', AnotherEnum.TWO)
    
    @classmethod
    def _missing_(cls, value):
        for item in cls:
            if item.value[0] == value:
                return item
        return super()._missing_(value)

I'd base my choice on whether looking up by description is a natural thing to do or not. If it's specific to translating JSON, rather stick with the alternate constructor. Otherwise, sure, go for this second option. However, in that case I'd wonder if the value is the best place to store the related AnotherEnum. Maybe instead you should have a method to_another_enum(), an alternate constructor on AnotherEnum, or both...?

Collectives™ on Stack Overflow

Getting enum object from string when enum values are tuples?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related