What is the total_ordering descriptor in functools in Python?

Functools module

The functools module in Python creates higher-order functions that interact with other functions. The higher-order functions either return other functions, or operate on them to broaden the scope of the function without modifying or explicitly defining them.

Comparison ordering methods of a class

Comparison ordering methods of a class are used for the comparison of class objects. There are six comparison ordering methods for any given class. They are as follows:

  • __lt__(): Lesser than method
  • __le__(): Lesser than or equal to method
  • __gt__(): Greater than method
  • __ge__(): Greater than or equal to method
  • __eq__(): Equal to method

total_ordering descriptor

Let’s imagine that we need to compare class objects. Hence, we have to provide the implementations of all the comparison ordering methods of the class. This requires a bit of effort.

However, we can simplify the process with the total_ordering descriptor. We can define any one of the comparison ordering methods, and the decorator supplies the rest of the methods. The class also must provide an __eq__() method.

Let’s consider we supply the __lt__ and __eq__ methods. The decorator supplies the rest of the comparison methods i.e., __le__(), __gt__(), and __ge__().

Code

from functools import total_ordering
@total_ordering
class Person:
    def __init__(self, age):
        self.age = age
    def __lt__(self, other):
        return self.age < other.age
    
    def __eq__(self, other):
        return self.age == other.age
person1 = Person(10)
person2 = Person(20)
print("Person(10) > Person(20) ? ", person1 > person2)
print("Person(10) == Person(20) ? ", person1 == person2)
print("Person(10) >= Person(20) ? ", person1 >= person2)
print("Person(10) < Person(20) ? ", person1 < person2)
print("Person(10) <= Person(20) ? ", person1 <= person2)

Explanation

  • Line 1: We import the total_ordering decorator.
  • Lines 3 to 13: We define a Person class decorated with total_ordering. The class has age as an attribute. We provide the implementations for the __lt__() and __eq__() methods considering the age attribute.
  • Lines 15 to 16: We define two Person objects called person1 and person2, with a different value for the age attributes of each.
  • Lines 17 to 21: We compare person1 and person2 using different comparison operators.

Free AI Mock Interviews
Coding Interview
Coding PatternsFree Interview
Gain insights and practical experience with coding patterns through targeted MCQs and coding problems, designed to match and challenge your expertise level.
System Design
You TubeFree Interview
Learn to design a video streaming platform like YouTube by tackling functional and non-functional requirements, core components, and high-level to detailed design challenges.

Free Resources

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)