How to get back name of the enum element?

Question

I have an enum defined like this:

def enum(**enums):
    return type('Enum', (), enums)

Status = enum(
       STATUS_OK=0,
       STATUS_ERR_NULL_POINTER=1, 
       STATUS_ERR_INVALID_PARAMETER=2)

I have a function that returns status as Status enum. How can I get the name of the enum value, and not just value?

>>> cur_status = get_Status()
>>> print(cur_status)
1

I would like to get STATUS_ERR_NULL_POINTER, instead of 1

Solution 1

You'd have to loop through the class attributes to find the matching name:

name = next(name for name, value in vars(Status).items() if value == 1)

The generator expression loops over the attributes and their values (taken from the dictionary produced by the vars() function) then returns the first one that matches the value 1.

Enumerations are better modelled by the enum library, available in Python 3.4 or as a backport for earlier versions:

from enum import Enum

class Status(Enum):
    STATUS_OK = 0
    STATUS_ERR_NULL_POINTER = 1 
    STATUS_ERR_INVALID_PARAMETER = 2

giving you access to the name and value:

name = Status(1).name  # gives 'STATUS_ERR_NULL_POINTER'
value = Status.STATUS_ERR_NULL_POINTER.value  # gives 1

Solution 2

2021 update: These answers are out of date. Using Python's standard Enum class,

cur_status.name

will return the name. (STATUS_ERR_NULL_POINTER)

To look up the enum knowing the name:

s = Status['STATUS_ERR_NULL_POINTER']

Solution 3

You don't need to loop through the Enum class but just access _member_map_.

>>> Status._member_map_['STATUS_OK']
<Status.STATUS_OK: 0>

Solution 4

Not sure which python version it was introduced, but the hidden attribute _value2member_map_ gives you what you want.

class Status(Enum):
    STATUS_OK=0
    STATUS_ERR_NULL_POINTER=1
    STATUS_ERR_INVALID_PARAMETER=2

str(Status._value2member_map_[1])

Out:

'Status.STATUS_ERR_NULL_POINTER'

View more solutions

Comments

[Nerman]

The question was to find an enum by value (in your example 0)

[interestedparty333]

This is useful but backwards :)

[Merlin1896]

You could simply use Status(1).name

[DeusXMachina]

Oh, that is much simpler!

[Ethan Furman]

The question is not about Python's Enum, but one the OP created.

[Ethan Furman]

The question is not about Python's Enum, but one the OP created.

[Ethan Furman]

The question is not about Python's Enum, but one the OP created.

[brandonscript]

OP should be using Python's enum :)