Python Lists Tutorial | List Operations, Methods, and Manipulation

What are Lists?

In Python, lists are ordered collections of items that can be of different data types. Lists are mutable, meaning you can modify them after creation. They are defined using square brackets [] and elements are separated by commas.

Lists are one of the most commonly used data structures in Python due to their flexibility and ease of use.

"Lists are Python's workhorse data type."

Creating Lists

You can create lists in several ways:

# Empty list
empty_list = []

# List with elements
numbers = [1, 2, 3, 4, 5]
fruits = ["apple", "banana", "cherry"]
mixed = [1, "hello", 3.14, True]

# Using list() constructor
list_from_string = list("hello")
list_from_range = list(range(5))

print(numbers)          # [1, 2, 3, 4, 5]
print(fruits)           # ['apple', 'banana', 'cherry']
print(mixed)            # [1, 'hello', 3.14, True]
print(list_from_string) # ['h', 'e', 'l', 'l', 'o']
print(list_from_range)  # [0, 1, 2, 3, 4]

Accessing List Elements

Lists support indexing and slicing:

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

# Indexing
print(fruits[0])   # 'apple' (first element)
print(fruits[2])   # 'cherry'
print(fruits[-1])  # 'elderberry' (last element)
print(fruits[-2])  # 'date'

# Slicing
print(fruits[1:4])  # ['banana', 'cherry', 'date']
print(fruits[:3])   # ['apple', 'banana', 'cherry']
print(fruits[2:])   # ['cherry', 'date', 'elderberry']
print(fruits[::2])  # ['apple', 'cherry', 'elderberry'] (every second element)

List Methods

Python provides numerous built-in methods for list manipulation:

Adding Elements:

fruits = ["apple", "banana"]

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

# extend() - Add multiple elements
fruits.extend(["date", "elderberry"])
print(fruits)  # ['apple', 'banana', 'cherry', 'date', 'elderberry']

# insert() - Insert at specific position
fruits.insert(1, "apricot")
print(fruits)  # ['apple', 'apricot', 'banana', 'cherry', 'date', 'elderberry']

Removing Elements:

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

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

# pop() - Remove and return element at index
last_fruit = fruits.pop()
print(last_fruit)  # 'banana'
print(fruits)      # ['apple', 'cherry']

# pop() with index
second_fruit = fruits.pop(1)
print(second_fruit)  # 'cherry'
print(fruits)        # ['apple']

# clear() - Remove all elements
fruits.clear()
print(fruits)  # []

Other Useful Methods:

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

# index() - Find index of element
print(numbers.index(4))  # 2

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

# sort() - Sort the list
numbers.sort()
print(numbers)  # [1, 1, 2, 3, 4, 5, 6, 9]

# reverse() - Reverse the list
numbers.reverse()
print(numbers)  # [9, 6, 5, 4, 3, 2, 1, 1]

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

List Comprehension

List comprehension is a concise way to create lists:

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

# With condition
even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares)  # [0, 4, 16, 36, 64]

# Nested list comprehension
matrix = [[i*j for j in range(3)] for i in range(3)]
print(matrix)  # [[0, 0, 0], [0, 1, 2], [0, 2, 4]]

# Converting strings to uppercase
fruits = ["apple", "banana", "cherry"]
upper_fruits = [fruit.upper() for fruit in fruits]
print(upper_fruits)  # ['APPLE', 'BANANA', 'CHERRY']

List Operations

Lists support various operations:

# Concatenation
list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined = list1 + list2
print(combined)  # [1, 2, 3, 4, 5, 6]

# Repetition
repeated = [1, 2] * 3
print(repeated)  # [1, 2, 1, 2, 1, 2]

# Membership testing
fruits = ["apple", "banana", "cherry"]
print("apple" in fruits)    # True
print("grape" not in fruits)  # True

# Length
print(len(fruits))  # 3

# Maximum and minimum
numbers = [1, 5, 3, 9, 2]
print(max(numbers))  # 9
print(min(numbers))  # 1
print(sum(numbers))  # 20

Nested Lists

Lists can contain other lists:

# Nested lists (2D lists)
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

print(matrix[0])     # [1, 2, 3]
print(matrix[1][2])  # 6 (row 1, column 2)

# Accessing elements
for row in matrix:
    for element in row:
        print(element, end=" ")
    print()  # New line after each row

Best Practices

When working with lists:

Use list comprehensions for concise and readable code
Be aware of shallow copying vs deep copying
Use appropriate methods for adding/removing elements
Consider memory usage with large lists
Use built-in functions like len(), max(), min(), sum()
Remember that lists are mutable - changes affect the original list

Lists are fundamental to Python programming and mastering them will help you handle collections of data effectively.