Python Sort with Custom Comparator: Complete Guide - TECH TU PEDIA

Python Sort with Custom Comparator: Complete Guide

Author: Amresh Mishra | Published On: July 7, 2023

Python Sort with Custom Comparator is a powerful feature that allows developers to fine-tune the sorting behavior of elements in Python. By utilizing a custom comparator, programmers can define their own rules for sorting data, enabling precise control over the ordering of elements.

Whether you need to sort a list of objects based on specific attributes or implement a specialized sorting algorithm, mastering Python Sort with Custom Comparator will empower you to efficiently manipulate and arrange data according to your exact requirements.

Understanding the Default Sort;

Before diving into custom comparators, let’s briefly understand how the default sort works in Python. The default behavior of the sort() function is to arrange elements in ascending order based on their natural order. For example, if we have a list of integers [3, 1, 4, 2] and we apply the default sort, the result will be [1, 2, 3, 4]. Similarly, for a list of strings such as [‘apple’, ‘banana’, ‘cherry’], the default sort will give us [‘apple’, ‘banana’, ‘cherry’] as the output.

Custom Comparator in Python

In some scenarios, the default sorting mechanism may not be sufficient. We may need to sort elements based on criteria that are not covered by the default comparison. In such cases, we can define a custom comparator function that provides the specific logic for sorting.

Writing a Custom Comparator Function:

To create a custom comparator in Python, we need to define a function that takes two elements as input and returns a value based on their relative order. The function should follow a specific convention where it returns a negative value if the first element should come before the second, a positive value if the first element should come after the second, or zero if the elements are equal in terms of sorting.

Let’s consider an example where we have a list of tuples representing students’ names and their corresponding grades:


students = [('Alice', 85), ('Bob', 92), ('Charlie', 78)]

Suppose we want to sort this list based on the students’ grades in descending order. We can define a custom comparator function that compares the second element of each tuple (the grade) and returns the difference between them:


def compare_grades(student1, student2): return student2[1] - student1[1]

Now, we can use the sort() function with the compare_grades function as the key argument to perform the sorting:


students.sort(key=compare_grades) After executing the above code, the students list will be sorted in descending order of grades: [(‘Bob’, 92), (‘Alice’, 85), (‘Charlie’, 78)].

Sorting with Lambda Functions:

While defining a separate comparator function is useful for complex comparisons, Python also provides a concise way to use lambda functions as comparators. Lambda functions are anonymous functions that can be defined in a single line. We can leverage lambda functions to create custom comparators directly within the sorting function call.

Let’s revisit the previous example of sorting students based on grades using a lambda function:


students.sort(key=lambda x: x[1], reverse=True)

In this case, the lambda function lambda x: x[1] takes each student tuple x and returns the second element x[1], which represents the grade. By setting reverse=True, we can sort the list in descending order of grades.

Sorting Objects with Custom Comparators:

In addition to sorting simple data types, we can also use custom comparators to sort objects based on specific attributes. Suppose we have a list of objects representing books, with attributes like title, author, and publication year. If we want to sort the books based on their publication year, we can define a custom comparator function that compares the publication years of two books.

Here’s an example:


class Book: def __init__(self, title, author, year): self.title = title = author self.year = year books = [Book('Book 1', 'Author A', 1990), Book('Book 2', 'Author B', 2005), Book('Book 3', 'Author C', 1985)] def compare_years(book1, book2): return book1.year - book2.year books.sort(key=compare_years)

After executing the code above, the books list will be sorted based on the publication year in ascending order.


Python provides powerful sorting capabilities through the sort() function. While the default sorting mechanism is suitable for many cases, there are situations where we need a custom comparator to sort elements based on specific criteria. By defining custom comparator functions or using lambda functions, we can tailor the sorting process to our needs. Whether sorting simple data types or objects, understanding how to use custom comparators in Python empowers us to arrange elements effectively in any desired order.


Author: Amresh Mishra
Amresh Mishra is the author of, a go-to resource for technology enthusiasts. With an MBA and extensive tech knowledge, Amresh offers insightful content on the latest trends and innovations in the tech world. His goal is to make complex tech concepts accessible and understandable for everyone, educating and engaging readers through his expertise and passion for technology.

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