How can you sort a list using Python?

1 The sort() method

The sort() method is a built-in method that modifies the original list by rearranging its elements in ascending or descending order. You can use the reverse parameter to specify the order, and the key parameter to define a custom sorting function. For example, you can sort a list of numbers by their absolute value, or a list of strings by their length. The sort() method is fast and efficient, but it changes the original list, which may not be desirable in some cases.

# Sort a list of numbers in ascending order
numbers = [5, -2, 9, 0, 1]
numbers.sort()
print(numbers) # [0, -2, 1, 5, 9]
# Sort a list of numbers in descending order by their absolute value
numbers = [5, -2, 9, 0, 1]
numbers.sort(reverse=True, key=abs)
print(numbers) # [9, 5, -2, 1, 0]
# Sort a list of strings by their length in ascending order
words = ["apple", "banana", "cherry", "date", "elderberry"]
words.sort(key=len)
print(words) # ["date", "apple", "banana", "cherry", "elderberry"]        

2 The sorted() function

The sorted() function is a built-in function that returns a new sorted list from any iterable object, such as a list, a tuple, a set, or a dictionary. The sorted() function has the same parameters as the sort() method, but it does not modify the original object. Instead, it creates a copy of the object and sorts it. The sorted() function is more flexible and versatile, but it uses more memory and may be slower than the sort() method.

# Sort a list of numbers in ascending order and assign it to a new variable
numbers = [5, -2, 9, 0, 1]
sorted_numbers = sorted(numbers)
print(sorted_numbers) # [0, -2, 1, 5, 9]
print(numbers) # [5, -2, 9, 0, 1]
# Sort a tuple of strings in descending order by their first letter
words = ("apple", "banana", "cherry", "date", "elderberry")
sorted_words = sorted(words, reverse=True, key=lambda x: x[0])
print(sorted_words) # ["elderberry", "date", "cherry", "banana", "apple"]
print(words) # ("apple", "banana", "cherry", "date", "elderberry")
# Sort a set of numbers in ascending order and convert it to a list
numbers = {5, -2, 9, 0, 1}
sorted_numbers = list(sorted(numbers))
print(sorted_numbers) # [-2, 0, 1, 5, 9]
print(numbers) # {0, 1, -2, 5, 9}        

3 The reversed() function

The reversed() function is a built-in function that returns a reversed iterator from any iterable object. The reversed() function does not sort the object, but simply reverses its order. You can use the reversed() function to reverse a list in place, or to create a new reversed list from any iterable object. The reversed() function is useful when you need to iterate over an object in reverse order, or when you need to reverse a list without sorting it.

# Reverse a list in place
numbers = [5, -2, 9, 0, 1]
numbers.reverse()
print(numbers) # [1, 0, 9, -2, 5]
# Create a new reversed list from a tuple
words = ("apple", "banana", "cherry", "date", "elderberry")
reversed_words = list(reversed(words))
print(reversed_words) # ["elderberry", "date", "cherry", "banana", "apple"]
print(words) # ("apple", "banana", "cherry", "date", "elderberry")
# Iterate over a list in reverse order
numbers = [5, -2, 9, 0, 1]
for number in reversed(numbers):
    print(number) # 1, 0, 9, -2, 5        

4 The list comprehension technique

The list comprehension technique is a concise and elegant way to create a new list from an existing one, by applying some transformation or filter to each element. You can use the list comprehension technique to sort a list by using a custom sorting function or a conditional expression. The list comprehension technique is powerful and expressive, but it may be less readable and more complex than the built-in methods and functions.

# Sort a list of numbers by their last digit in ascending order
numbers = [5, -2, 9, 0, 1]
sorted_numbers = [x for x in sorted(numbers, key=lambda x: x % 10)]
print(sorted_numbers) # [0, -2, 1, 5, 9]
# Sort a list of strings by their second letter in descending order, only if they start with "a"
words = ["apple", "banana", "cherry", "date", "elderberry"]
sorted_words = [x for x in sorted(words, reverse=True, key=lambda x: x[1]) if x[0] == "a"]
print(sorted_words) # ["apple"]        

5 The operator module

The operator module is a built-in module that provides a set of functions that correspond to the common operators in Python, such as arithmetic, comparison, logical, and bitwise operators. You can use the operator module to sort a list by using one of its functions as the key parameter, instead of writing a lambda function. The operator module can make your code more concise and clear, but it may not cover all the possible sorting criteria that you need.

# Sort a list of tuples by their second element in ascending order
tuples = [(1, 5), (2, 4), (3, 3), (4, 2), (5, 1)]
import operator
sorted_tuples = sorted(tuples, key=operator.itemgetter(1))
print(sorted_tuples) # [(5, 1), (4, 2), (3, 3), (2, 4), (1, 5)]
# Sort a list of dictionaries by their "name" key in descending order
dictionaries = [{"name": "Alice", "age": 25}, {"name": "Bob", "age": 30}, {"name": "Charlie", "age": 35}]
import operator
sorted_dictionaries = sorted(dictionaries, reverse=True, key=operator.itemgetter("name"))
print(sorted_dictionaries) # [{"name": "Charlie", "age": 35}, {"name": "Bob", "age": 30}, {"name": "Alice", "age": 25}]        

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?