Comparison magic methods in Python

Introduction

Comparison magic methods let you decide how objects compare to each other using operators like <, >, ==, and more.

When you want to compare two custom objects to see if they are equal.

When sorting a list of your custom objects based on some property.

When checking if one object is greater or smaller than another.

When using comparison operators in conditions with your own classes.

Syntax

Python

def __eq__(self, other):
    # return True if self equals other

def __lt__(self, other):
    # return True if self is less than other

def __le__(self, other):
    # return True if self is less than or equal to other

def __gt__(self, other):
    # return True if self is greater than other

def __ge__(self, other):
    # return True if self is greater than or equal to other

def __ne__(self, other):
    # return True if self is not equal to other

Each method should return a boolean (True or False).

Use these methods inside your class to customize how comparison operators work.

Examples

Checks if two objects have the same 'value' property.

Python

def __eq__(self, other):
    return self.value == other.value

Returns True if self's value is less than other's value.

Python

def __lt__(self, other):
    return self.value < other.value

Returns True if values are not equal.

Python

def __ne__(self, other):
    return self.value != other.value

Sample Program

This program creates a Box class with a volume. It compares boxes by their volume using ==, <, and > operators.

Python

class Box:
    def __init__(self, volume):
        self.volume = volume

    def __eq__(self, other):
        return self.volume == other.volume

    def __lt__(self, other):
        return self.volume < other.volume

    def __gt__(self, other):
        return self.volume > other.volume

box1 = Box(10)
box2 = Box(20)
box3 = Box(10)

print(box1 == box2)  # False
print(box1 == box3)  # True
print(box1 < box2)   # True
print(box2 > box3)   # True

Important Notes

Only __eq__ and __ne__ are required for equality checks; others are for ordering.

If you define __eq__, also define __ne__ for consistent behavior.

Python can use functools.total_ordering to fill in missing comparison methods if you define __eq__ and one ordering method.

Summary

Comparison magic methods let you control how objects compare with ==, <, >, etc.

Define these methods inside your class to customize comparisons.

They return True or False based on your rules.