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Data Structures - Lists

Apr 1, 2026•5 min read•By Mohammed Vasim
PythonProgrammingTutorialBeginner

Introduction

In this tutorial, you'll learn about Python lists - one of the most versatile and commonly used data structures. Lists allow you to store multiple items in a single variable, making it easy to work with collections of data.

What You'll Learn

  • Creating lists
  • Accessing list elements (indexing and slicing)
  • Modifying lists (adding, removing, updating)
  • List methods and operations
  • Iterating over lists
  • List comprehension

What are Lists?

Lists are ordered collections of items. They can hold values of any type and are mutable (you can change them after creation).

python
# Creating a list
fruits = ["apple", "banana", "cherry"]
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

print(fruits)    # Output: ['apple', 'banana', 'cherry']
print(numbers)   # Output: [1, 2, 3, 4, 5]
print(mixed)     # Output: [1, 'hello', 3.14, True]

Creating Lists

python
# Empty list
empty = []
print(empty)     # Output: []

# List with initial values
colors = ["red", "green", "blue"]

# Using the list() constructor
numbers = list(range(5))    # [0, 1, 2, 3, 4]
print(numbers)

# List with repeated values
zeros = [0] * 5             # [0, 0, 0, 0, 0]
print(zeros)

Accessing Elements

Indexing

Each element has an index starting from 0:

python
fruits = ["apple", "banana", "cherry", "date", "elderberry"]

print(fruits[0])   # apple (first)
print(fruits[1])   # banana (second)
print(fruits[2])   # cherry (third)

# Negative indexing (from the end)
print(fruits[-1])  # elderberry (last)
print(fruits[-2])  # date (second to last)

Slicing

Get a portion of the list:

python
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

print(numbers[2:6])    # [2, 3, 4, 5] (index 2 to 5)
print(numbers[:5])     # [0, 1, 2, 3, 4] (start to 4)
print(numbers[5:])     # [5, 6, 7, 8, 9] (5 to end)
print(numbers[::2])    # [0, 2, 4, 6, 8] (every other)
print(numbers[::-1])   # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] (reversed)

Modifying Lists

Changing Elements

python
fruits = ["apple", "banana", "cherry"]

fruits[0] = "orange"
print(fruits)    # ['orange', 'banana', 'cherry']

fruits[-1] = "grape"
print(fruits)    # ['orange', 'banana', 'grape']

Adding Elements

python
fruits = ["apple", "banana"]

# append() - add to end
fruits.append("cherry")
print(fruits)    # ['apple', 'banana', 'cherry']

# insert() - add at specific position
fruits.insert(1, "orange")
print(fruits)    # ['apple', 'orange', 'banana', 'cherry']

# extend() - add multiple items
fruits.extend(["grape", "melon"])
print(fruits)    # ['apple', 'orange', 'banana', 'cherry', 'grape', 'melon']

# Using + operator
fruits = fruits + ["kiwi", "lime"]
print(fruits)    # Adds to the end

Removing Elements

python
fruits = ["apple", "banana", "cherry", "banana"]

# remove() - removes first occurrence
fruits.remove("banana")
print(fruits)    # ['apple', 'cherry', 'banana']

# pop() - removes and returns last item
item = fruits.pop()
print(item)      # banana
print(fruits)    # ['apple', 'cherry']

# pop() with index
fruits.pop(0)
print(fruits)    # ['cherry']

# clear() - remove all items
fruits.clear()
print(fruits)    # []

# del statement
fruits = ["apple", "banana", "cherry"]
del fruits[1]
print(fruits)    # ['apple', 'cherry']

List Methods

Python provides many built-in methods for lists:

python
numbers = [3, 1, 4, 1, 5, 9, 2, 6]

# Sorting
numbers.sort()
print(numbers)       # [1, 1, 2, 3, 4, 5, 6, 9]

# Reverse sorting
numbers.sort(reverse=True)
print(numbers)       # [9, 6, 5, 4, 3, 2, 1, 1]

# Reverse without sorting
numbers.reverse()
print(numbers)       # [1, 1, 2, 3, 4, 5, 6, 9]

# Index of first occurrence
print(numbers.index(5))   # 4

# Count occurrences
print(numbers.count(1))   # 2

# Copy a list
numbers_copy = numbers.copy()
print(numbers_copy)       # [1, 1, 2, 3, 4, 5, 6, 9]

Common Methods Table

MethodDescriptionExample
append(item)Add to endlist.append(x)
insert(i, x)Insert at indexlist.insert(0, x)
extend(iterable)Add multiplelist.extend([x, y])
remove(x)Remove first xlist.remove(x)
pop(i)Remove at indexlist.pop()
clear()Remove alllist.clear()
index(x)Find indexlist.index(x)
count(x)Count occurrenceslist.count(x)
sort()Sort in placelist.sort()
reverse()Reverse in placelist.reverse()

Iterating Over Lists

python
fruits = ["apple", "banana", "cherry"]

# Basic for loop
for fruit in fruits:
    print(fruit)

# With index using enumerate()
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Using range
for i in range(len(fruits)):
    print(fruits[i])

List Comprehension

A concise way to create lists:

Basic Syntax

python
# Instead of:
squares = []
for i in range(10):
    squares.append(i ** 2)

# Use comprehension:
squares = [i ** 2 for i in range(10)]
print(squares)   # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

With Condition

python
# Even numbers only
evens = [i for i in range(10) if i % 2 == 0]
print(evens)     # [0, 2, 4, 6, 8]

# With if-else
labels = ["even" if i % 2 == 0 else "odd" for i in range(5)]
print(labels)    # ['even', 'odd', 'even', 'odd', 'even']

Practical Examples

python
# Uppercase strings
fruits = ["apple", "banana", "cherry"]
upper = [f.upper() for f in fruits]
print(upper)     # ['APPLE', 'BANANA', 'CHERRY']

# Flatten a 2D list
matrix = [[1, 2], [3, 4], [5, 6]]
flat = [num for row in matrix for num in row]
print(flat)      # [1, 2, 3, 4, 5, 6]

Common Patterns

Finding Sum, Min, Max

python
numbers = [3, 1, 4, 1, 5, 9, 2, 6]

print(sum(numbers))   # 31
print(min(numbers))   # 1
print(max(numbers))   # 9
print(len(numbers))   # 8

Checking if Item Exists

python
fruits = ["apple", "banana", "cherry"]

print("apple" in fruits)    # True
print("grape" in fruits)    # False

Summary

In this tutorial, you learned:

  • ✅ Creating and initializing lists
  • ✅ Accessing elements (indexing and slicing)
  • ✅ Modifying lists (adding, removing, updating)
  • ✅ List methods (sort, reverse, etc.)
  • ✅ Iterating over lists
  • ✅ List comprehension

🧑‍💻 Practice Exercise

Create a program that:

  1. Creates a list of 5 numbers
  2. Finds and prints the sum, average, max, and min
  3. Removes the largest number and prints the updated list
  4. Creates a new list with each number doubled
Click to see solution
python
# List operations practice
numbers = [10, 25, 5, 40, 15]

# Find sum, average, max, min
total = sum(numbers)
average = total / len(numbers)
maximum = max(numbers)
minimum = min(numbers)

print("--- Statistics ---")
print(f"Sum: {total}")
print(f"Average: {average}")
print(f"Max: {maximum}")
print(f"Min: {minimum}")

# Remove largest number
numbers.remove(max(numbers))
print(f"\nAfter removing max: {numbers}")

# Double each number
doubled = [num * 2 for num in numbers]
print(f"Doubled: {doubled}")

Output:

--- Statistics --- Sum: 95 Average: 19.0 Max: 40 Min: 5 After removing max: [10, 25, 5, 15] Doubled: [20, 50, 10, 30]

What's Next

In the next tutorial, we'll learn about Dictionaries & Tuples - more ways to organize and store data.

Data Structures - Dictionaries & Tuples →

← PreviousControl Flow - LoopsNext →Data Structures - Dictionaries & Tuples

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