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How to Check for Value or Name Membership in Python Enums

Python's Enum class provides a way to create symbolic names for constant values.

This guide explains how to check if a specific value or name exists within an Enum, using both list comprehensions and the more direct in operator on the Enum itself.

Checking if a Value Exists in an Enum​

The most straightforward and Pythonic way to check if a value exists in an Enum is to use the in operator directly with a list of the Enum's values.

from enum import Enum

class Sizes(Enum):
    SMALL = 1
    MEDIUM = 2
    LARGE = 3

values = [member.value for member in Sizes]
if 2 in values:
    print('2 is in enum values')  # Output: 2 is in enum values
else:
    print("Value not found")
print(100 in values) # Output: False
  • Using a list comprehension extracts all enum values.
  • The in operator then checks for membership in the list of extracted values.

Using a List Comprehension (Less Efficient)​

You could technically create a list comprehension and check for value existence:

from enum import Enum

class Sizes(Enum):
    SMALL = 1
    MEDIUM = 2
    LARGE = 3

values = [member.value for member in Sizes]
print(values)  # Output: [1, 2, 3]

if 2 in values: # Check the values list
    print('2 is in enum values')
else:
    print("Value is not found")
  • You first create a list using a list comprehension, iterating over the Enum members, and extracting the value for each.
  • The in keyword is used to check if the list has the value you are looking for.
  • Disadvantage: This approach is less efficient than the direct in test, as it requires creating a temporary list of the enum's values.

Checking if a Name Exists in an Enum​

To check if a particular name (the string representation of the enum member, e.g., 'SMALL') exists within an Enum, you have two main options.

Direct in Membership Test on __members__ (Recommended)​

The best approach is to use the in operator directly with the __members__ attribute of the Enum class:

from enum import Enum
class Sizes(Enum):
    SMALL = 1
    MEDIUM = 2
    LARGE = 3

print(Sizes.__members__)
# Output: {'SMALL': <Sizes.SMALL: 1>, 'MEDIUM': <Sizes.MEDIUM: 2>, 'LARGE': <Sizes.LARGE: 3>}

if 'SMALL' in Sizes.__members__:
    print('SMALL is in enum names') # Output: SMALL is in enum names
else:
    print("Name not found")
  • Sizes.__members__: This is a read-only, ordered mapping (similar to a dictionary) that maps the names of the enum members to the members themselves.
  • in Sizes.__members__: This directly checks if the string 'SMALL' is a key in the __members__ mapping. This is very efficient (like checking for a key in a dictionary).

Using a List Comprehension (Less Efficient)​

You could also create a list of names and then use in:

from enum import Enum

class Sizes(Enum):
    SMALL = 1
    MEDIUM = 2
    LARGE = 3
names = [member.name for member in Sizes]
print(names)  # Output: ['SMALL', 'MEDIUM', 'LARGE']

if 'SMALL' in names:
    print('SMALL is in enum names')
else:
    print("Name not found")
  • This approach is less efficient than using the in operator directly on __members__, as it needs to first create a list containing all of the enum values.

Conclusion​

This guide presented various methods for checking whether a value or a name exists within a Python Enum. The recommended and most efficient methods are:

  • For value existence: Create a list containing all the values of the enum, and use the in operator to check if the value exists in the list.
  • For name existence: Use the in operator directly on the __members__ attribute of the Enum class (if 'NAME' in MyEnum.__members__:).

These direct checks leverage Python's built-in optimizations for membership testing and are more readable than creating intermediate lists. Avoid list comprehensions for simple membership checks in Enums.

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