Making classes support comparison operations in Python

Making Classes Support Comparison Operations

Problem

You’d like to be able to compare instances of your class using the standard comparison operators (e.g., >=, !=, <=, etc.), but without having to write a lot of special methods.

Solution

Python classes can support comparison by implementing a special method for each comparison operator. For example, to support the >= operator, you define a __ge__() method in the classes. Although defining a single method is usually no problem, it quickly gets tedious to create implementations of every possible comparison operator.

The functools.total_ordering decorator can be used to simplify this process. To use it, you decorate a class with it, and define __eq__() and one other comparison method (__lt__, __le__, __gt__, or __ge__). The decorator then fills in the other comparison methods for you.

As an example, let’s build some houses and add some rooms to them, and then perform comparisons based on the size of the houses:

from functools import total_ordering
class Room(object):
    def __init__(self, name, length, width):
        self.name = name
        self.length = length
        self.width = width
        self.square_feet = self.length * self.width

@total_ordering
class House(object):
    def __init__(self, name, style):
        self.name = name
        self.style = style
        self.rooms = list()

    @property
    def living_space_footage(self):
        return sum(r.square_feet for r in self.rooms)

    def add_room(self, room):
        self.rooms.append(room)

    def __str__(self):
        return '{}: {} square foot {}'.format(self ...