Python List sort() method [With Examples]

In this Python article, we will take a deep dive into the Python List sort() method – a powerful and handy technique for sorting the elements of a Python list.

We will cover its syntax, usage, and explore some examples to better understand its practical applications.

List sort() method in Python

Below are the topics that we are doing to discuss in this article:

• Introduction to Python List sort() method
• Syntax of the sort() method
• Purpose and use cases of the sort() method

Python List sort() method

The list sort() method in Python is a built-in method that allows you to sort a list of items in ascending or descending order, depending on the specified parameters.

The method operates in-place, which means that the original Python list is modified instead of returning a new, sorted Python list.

Syntax:

The syntax for the list sort() method is as follows:

list.sort(key=None, reverse=False)

Parameters:

The list sort() method accepts two optional parameters:

1. key: A function that serves as a custom sorting criteria. This function takes an item as input and returns a value used for sorting. By default, the key parameter is set to None, which means that the items will be sorted based on their natural ordering.
2. reverse: A boolean value that, if set to True, sorts the list in descending order. By default, the reverse parameter is set to False, which means that the list will be sorted in ascending order.

sort() method in Python List Examples

Let’s explore a few examples to illustrate the usage of the list sort() method.

Example#1 Sorting a list of numbers in ascending order

temperatures = [68, 32, 55, 79, 42]
temperatures.sort()
print(temperatures)  

The Python list of temperatures (in Fahrenheit) recorded in different cities is sorted in ascending order using the sort() method. The result is a Python list of temperatures ordered from the lowest to the highest.

Output:

Example#2 Sorting a list of strings in descending order

states = ['Texas', 'California', 'New York', 'Florida', 'Washington']
states.sort(reverse=True)
print(states) 

The Python list of US states is sorted in descending alphabetical order using the sort() method with the reverse parameter set to True. The result is a Python list of states ordered from Z to A.

Output:

Example#3 Sorting a list of dictionaries based on a specific key

cities = [
    {'name': 'Los Angeles', 'population': 3898747},
    {'name': 'New York', 'population': 8336817},
    {'name': 'Chicago', 'population': 2693976},
]

cities.sort(key=lambda x: x['population'])
print(cities)

The Python list of US cities, represented as dictionaries with their respective populations, is sorted in ascending order based on their populations. The Python sort() method uses a lambda function as the key parameter to extract the population value from each dictionary.

Output:

Example#4 Sorting a list of tuples based on the second element

landmarks = [
    (37.7749, -122.4194),  # San Francisco
    (40.7128, -74.0060),   # New York City
    (34.0522, -118.2437),  # Los Angeles
    (41.8781, -87.6298),   # Chicago
    (47.6062, -122.3321),  # Seattle
]

landmarks.sort(key=lambda x: x[0])  # Sorting by latitude
print(landmarks)  

The Python list of GPS coordinates representing the latitude and longitude of famous US landmarks is sorted in ascending order based on latitude. The Python sort() method uses a lambda function as the key parameter to extract the latitude value (the first element) from each tuple.

The result is a Python list of landmarks ordered from the southernmost to the northernmost.

Output:

Example#5 Sorting a list of movie titles in alphabetical order

movies = ['The Godfather', 'Pulp Fiction', 'Forrest Gump', 'The Shawshank Redemption', 'Inception']
movies.sort()
print(movies)

The Python list of movie titles is sorted in alphabetical order using the sort() method. The result is a Python list of movies ordered from A to Z.

Output:

Conclusion

The Python list sort() method provides a powerful and flexible way to order the elements of a list based on their natural ordering or custom sorting criteria. The method offers optional parameters, such as key and reverse, to help us customize the sorting process according to our needs.

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