Lists in Python
In this article, we will take a detailed look at lists in Python — one of the most flexible and frequently used data types. Lists allow you to store collections of elements and manipulate them in various ways.
What is a list?
A list in Python is an ordered, mutable collection of elements that can be of different types. You can think of a list as a container that stores various objects arranged in a specific order.
The main properties of lists:
- Ordered: elements are stored in the order they were added
- Mutable: you can add, remove, and change elements after creating the list
- Indexable: each element can be accessed by its position (index)
- Allow duplicates: the same element can appear in the list multiple times
Creating lists
There are several ways to create lists in Python:
Using square brackets []
# Empty list >>> empty_list = [] >>> print(empty_list)[]# List of numbers >>> numbers = [1, 2, 3, 4, 5] >>> print(numbers)[1, 2, 3, 4, 5]# List of different data types >>> mixed = [1, "hello", True, 3.14] >>> print(mixed)[1, 'hello', True, 3.14]# Nested lists (list of lists) >>> matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] >>> print(matrix)[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Using the list() constructor
# Creating an empty list >>> empty_list = list() >>> print(empty_list)[]# Creating a list from a string (each character becomes an element) >>> chars = list("Python") >>> print(chars)['P', 'y', 't', 'h', 'o', 'n']# Creating a list from other iterable objects >>> tuple_to_list = list((1, 2, 3)) >>> print(tuple_to_list)[1, 2, 3]>>> set_to_list = list({1, 2, 3}) >>> print(set_to_list)[1, 2, 3]
Using list comprehensions
# Creating a list of squares of numbers from 0 to 9 >>> squares = [x**2 for x in range(10)] >>> print(squares)[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]# Creating a list of even numbers from 0 to 9 >>> even_numbers = [x for x in range(10) if x % 2 == 0] >>> print(even_numbers)[0, 2, 4, 6, 8]
Accessing list elements
Indexing
In Python, indexing starts at 0, meaning the first element has index 0, the second one has index 1, and so on:
>>> fruits = ["apple", "banana", "cherry", "pear", "orange"] # Getting elements by index >>> first_fruit = fruits[0] >>> print(f"First fruit: {first_fruit}")First fruit: apple# Negative indices for accessing from the end of the list >>> last_fruit = fruits[-1] >>> print(f"Last fruit: {last_fruit}")Last fruit: orange>>> second_last = fruits[-2] >>> print(f"Second to last fruit: {second_last}")Second to last fruit: pear
Slices
Slices allow you to get a sublist by specifying start and end indices:
>>> fruits = ["apple", "banana", "cherry", "pear", "orange"] # Slice syntax: list[start:end:step] # Start is included, end is not included! # First three elements >>> first_three = fruits[0:3] >>> print(f"First three fruits: {first_three}")First three fruits: ['apple', 'banana', 'cherry']# Same thing, but the starting index can be omitted if it's 0 >>> first_three = fruits[:3] >>> print(f"First three fruits: {first_three}")First three fruits: ['apple', 'banana', 'cherry']# Every second element >>> every_second = fruits[::2] >>> print(f"Every second fruit: {every_second}")Every second fruit: ['apple', 'cherry', 'orange']# Reversing the list >>> reversed_list = fruits[::-1] >>> print(f"List in reverse order: {reversed_list}")List in reverse order: ['orange', 'pear', 'cherry', 'banana', 'apple']
Modifying list elements
Unlike strings, lists are mutable, meaning you can change, add, and remove elements:
>>> fruits = ["apple", "banana", "cherry"] # Changing an element >>> fruits[0] = "kiwi" >>> print(fruits)['kiwi', 'banana', 'cherry']# Changing multiple elements using a slice >>> numbers = [1, 2, 3, 4, 5] >>> numbers[1:4] = [20, 30, 40] >>> print(numbers)[1, 20, 30, 40, 5]# You can even replace multiple elements with a different number of elements >>> numbers = [1, 2, 3, 4, 5] >>> numbers[1:4] = [20, 30] >>> print(numbers)[1, 20, 30, 5]
Main list methods
Python provides many built-in methods for working with lists:
Adding elements
>>> fruits = ["apple", "banana"] # Adding an element to the end of the list >>> fruits.append("cherry") >>> print(fruits)['apple', 'banana', 'cherry']# Inserting an element at a specific position >>> fruits.insert(1, "orange") >>> print(fruits)['apple', 'orange', 'banana', 'cherry']# Adding elements from another list >>> more_fruits = ["pear", "grape"] >>> fruits.extend(more_fruits) >>> print(fruits)['apple', 'orange', 'banana', 'cherry', 'pear', 'grape']# Combining lists using the + operator >>> combined = fruits + ["pineapple", "mango"] >>> print(combined)['apple', 'orange', 'banana', 'cherry', 'pear', 'grape', 'pineapple', 'mango']
Removing elements
>>> fruits = ["apple", "banana", "cherry", "orange", "banana"] # Removing an element by value (removes only the first occurrence) >>> fruits.remove("banana") >>> print(fruits)['apple', 'cherry', 'orange', 'banana']# Removing an element by index and returning its value >>> removed = fruits.pop(1) >>> print(f"Removed: {removed}")Removed: cherry>>> print(f"List after removal: {fruits}")List after removal: ['apple', 'orange', 'banana']# If no index is specified, pop() removes and returns the last element >>> last = fruits.pop() >>> print(f"Last element: {last}")Last element: banana>>> print(fruits)['apple', 'orange']# Removing all elements from the list >>> fruits.clear() >>> print(f"Empty list: {fruits}")Empty list: []# The del operator for removing elements by index or slice >>> numbers = [1, 2, 3, 4, 5] >>> del numbers[0] >>> print(numbers)[2, 3, 4, 5]>>> del numbers[1:3] >>> print(numbers)[2, 5]
Finding and counting elements
>>> fruits = ["apple", "banana", "cherry", "banana", "pear"] # Checking if an element is in the list >>> print("banana" in fruits)True>>> print("watermelon" in fruits)False# Finding the index of the first occurrence of an element >>> banana_index = fruits.index("banana") >>> print(f"Index of the first banana: {banana_index}")Index of the first banana: 1# Counting the number of occurrences of an element >>> banana_count = fruits.count("banana") >>> print(f"Number of bananas: {banana_count}")Number of bananas: 2
Sorting and reversing
# Sorting a list (modifies the original list) >>> numbers = [3, 1, 4, 1, 5, 9, 2] >>> numbers.sort() >>> print(f"Sorted list: {numbers}")Sorted list: [1, 1, 2, 3, 4, 5, 9]# Sorting in reverse order >>> numbers.sort(reverse=True) >>> print(f"Reverse sort: {numbers}")Reverse sort: [9, 5, 4, 3, 2, 1, 1]# If you don't want to modify the original list, use sorted() >>> original = [3, 1, 4, 1, 5] >>> sorted_list = sorted(original) >>> print(f"Original: {original}")Original: [3, 1, 4, 1, 5]>>> print(f"Sorted copy: {sorted_list}")Sorted copy: [1, 1, 3, 4, 5]
Copying lists
When working with lists, it's important to understand how assignment and copying work:
# Create a list >>> original = [1, 2, 3] # Assignment doesn't create a copy — both variables point to the same list >>> reference = original >>> reference.append(4) >>> print(f"Original after changing the reference: {original}")Original after changing the reference: [1, 2, 3, 4]# Correct ways to copy a list: # 1. The copy() method >>> copy1 = original.copy() # 2. Using slice [:] >>> copy2 = original[:] # 3. The list() function >>> copy3 = list(original) # Let's check that the copies are not linked to the original >>> copy1.append(5) >>> print(f"Original: {original}")Original: [1, 2, 3, 4]>>> print(f"Copy 1: {copy1}")Copy 1: [1, 2, 3, 4, 5]
Practical example of using a list
# List of students and their grades >>> students = ["Anna", "John", "Maria", "Peter", "Elena"] >>> grades = [95, 82, 90, 78, 88] # Finding the student with the highest score >>> highest_score = max(grades) >>> top_student_index = grades.index(highest_score) >>> print(f"Best student: {students[top_student_index]} with a grade of {highest_score}")Best student: Anna with a grade of 95
Understanding check
Which of the following methods will correctly create a copy of a list that is not linked to the original?