How to Type Hint Enums in Python

Learn how to properly type hint Python enums using the Enum class or Literal type for better code clarity and type safety in static analysis tools.

Enums (enumerations) provide a way to create sets of named constants in Python, making your code more readable and maintainable. When working with enums, using type hints can further enhance code quality by allowing type checkers to catch errors early.

Type Hinting Enums with the Enum Class

The most straightforward and recommended way to type hint an enum is by using the enumeration class itself as the type annotation.

from enum import Enum

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

def get_value_from_enum(size: Sizes) -> int:
    print(size.name)
    print(size.value)
    return size.value

result = get_value_from_enum(Sizes.MEDIUM)
print(result)

Explanation:

We import the Enum class from the enum module.
We define an enum called Sizes with three members: SMALL, MEDIUM, and LARGE.
In the get_value_from_enum function, we specify the parameter size as type Sizes. This tells the type checker that the size parameter must be one of the members from the Sizes enum.
Inside the function, we can access members of enum using the .name and .value properties.
We also add the return type of the function, which is int as the size.value returns integer value.
The get_value_from_enum function is then called with Sizes.MEDIUM as its argument.

Type Hinting Enums with the `Literal` Type

Another approach is to use the Literal type from the typing module. The Literal type allows you to specify that a variable or parameter must have one of several specific literal values, like the enum members.

from typing import Literal
from enum import Enum

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

def get_value_from_enum(size: Literal[Sizes.SMALL, Sizes.MEDIUM, Sizes.LARGE]) -> int:
    print(size.name)
    print(size.value)
    return size.value

result = get_value_from_enum(Sizes.MEDIUM)
print(result)