Array-based enum in python

Question

I am looking for an enum-based approach to return an array behind each enum item. For example, suppose that I need to specify a range for each type of target such as the following:

from enum import Enum 

class TargetRange(Enum):
    T1 = [0, 100]
    T2 = [30, 60]
    T3 = [50, 150]

Now, I am using the enum like the following:

target_range = TargetRange.T1
value = 140

# ...
# adjust the value

if(value > target_range[1]):
    value = target_range[1]
elif(value < target_range[0]):
    value = target_range[0]
# ...

But, I get the following error:

TypeError: 'TargetRange' object is not subscriptable

How can I resolve it? What is the correct usage of this kind of enum?

I should note that I found this post to return a string (instead of an array). Hence, I am looking for the same idea for returning array instead of a string.

Ethan Furman · Accepted Answer · 2022-11-16T14:53:32.233

There are three ways to get support for indexing:

use the .value attribute
```
TargetRange.T1.value
```
inherit from list as well as Enum:
```
class TargetRange(list, Enum):
```

add the __getitem__ method:

class TargetRange(Enum):
    def __getitem__(self, index):
        return self._value_[index]
    T1 = [0, 100]
    T2 = [30, 60]
    T3 = [50, 150]

It is also possible to add behavior to Python enums, which can simplify code elsewhere. For example:

class TargetRange(Enum):
    T1 = [0, 100]
    T2 = [30, 60]
    T3 = [50, 150]
    #
    def __getitem__(self, index):
        return self._value_[index]
    #
    def limit(self, value):
        # adjust the value
        if(value > self[1]):
            value = self[1]
        elif(value < self[0]):
            value = self[0]
        return value

then in the main code:

>>> TargetRange.T1.limit(140)
100

Disclosure: I am the author of the Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) library.

score 1 · Answer 2 · answered Oct 19 '21 at 14:06

The difference between Enum and StrEnum is exactly at this point. If you print TargetRange.T1, you will find that the value of the enum item is not returned. Hence, a simple solution to resolve this issue is rewriting your first line of the code as follow:

target_range = TargtetRange.T1.value
#...

It means using .value property of the enum item instead of directly using the enum item.

Array-based enum in python

2 Answers2