Python Enum

Python’s Enum

In Python, an enumeration is a data type used to create named constants, making code clearer and easier to read. In this article, we will detail the usage and features of enumerations in Python.

What is an Enum?

An enum is a data type in Python that is used to create a set of named constants. In traditional programming, we often use constants to represent fixed values, such as “LEFT,” “RIGHT,” “UP,” and “DOWN,” which represent directions. Enums can better manage these constants, making the code more readable and maintainable.

How to Use Enums

In Python, we can use the enum module to create Enums. We first import the Enum class, then create our own Enum class by inheriting from it.

from enum import Enum

class Direction(Enum):
LEFT = 1
RIGHT = 2
UP = 3
DOWN = 4

print(Direction.LEFT)

In the code above, we define an Enum class called Direction, which contains four constants: LEFT, RIGHT, UP, and DOWN. We can access the value of the constant LEFT by accessing Direction.LEFT.

Comparing Enum Constants

When we compare constants created using Enums, Python automatically handles the comparison for us. Enum constants are compared based on their values, not their names.

from enum import Enum

class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3

print(Color.RED == Color.GREEN) # False
print(Color.GREEN == Color.GREEN) # True

In the example above, we define an Enum class named Color that contains three color constants. We can compare the values of Enum constants using the == operator.

Accessing the Names and Values of Enum Constants

In Enum, we can access constants not only by their values but also by their names. We can use the .name and .value attributes to obtain the constant’s name and value.

from enum import Enum

class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3

print(Color.RED.name) # RED
print(Color.RED.value) # 1

In the above code, we use Color.RED.name and Color.RED.value to obtain the name and value of the constant RED, respectively.

Iterating Over Enum Constants

We can use the __members__ property of the Enum class to iterate over all the constants in the Enum class. This property returns a dictionary whose keys are the constant names and whose values are the constants themselves.

from enum import Enum

class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3

for color_name, color_obj in Color.__members__.items():
print(color_name, color_obj.value)

In the above code, we iterate over Color.__members__ to print the names and values of all the color constants.

Using Custom Values with Enum

When creating an Enum class, we can specify custom values for each constant. This can be useful in some cases, such as when we need a constant to have a specific value or behavior.

from enum import Enum

class Season(Enum):
SPRING = (1, "warm")
SUMMER = (2, "hot")
AUTUMN = (3, "cool")
WINTER = (4, "cold")

def __init__(self, temperature, description):
self.temperature = temperature
self.description = description

def get_temperature(self):
return self.temperature

print(Season.SUMMER.description) # hot
print(Season.SUMMER.get_temperature()) # 2

In the example above, we specify a custom value for each season constant, including a temperature and description, and define a get_temperature method to get the constant’s temperature value.

Using Enum and Inheriting IntEnum

In addition to inheriting from the Enum class, we can also inherit from the IntEnum class to create an integer-based Enum, which makes numerical comparisons more convenient.

from enum import IntEnum

class Priority(IntEnum):
LOW = 1
MEDIUM = 2
HIGH = 3

print(Priority.LOW < Priority.MEDIUM) # True

In the above example, we define an Enum class named Priority and inherit from the IntEnum class. This allows us to directly use operators such as < and > to compare the magnitudes of Enum constants.

Uses of Enums

• Clearly Represent Constants: Enums can clearly represent a group of related constants, making code easier to read and maintain.
• Avoid Hardcoding: When using Enums, we can avoid hard-coding constant values, improving code maintainability.
• Improve Readability: The names and values of Enum constants are readable, making code easier to understand.

Summary

In this article, we introduced the usage and features of Enums in Python in detail, including how to define the Enum class, compare constants, access constant names and values, iterate over Enum constants, customize constant values, and extend the IntEnum class. Using Enums allows us to better manage constants, making code clearer and easier to read.