Lists

Introduction

Lists are ordered, mutable collections that can hold items of different types.

Creating and Accessing

fruits = ["apple", "banana", "cherry", "date"]
numbers = [1, 2, 3, 4, 5]

# Accessing
print(fruits[0])     # apple
print(fruits[-1])    # date

# Slicing
print(numbers[1:4])  # [2, 3, 4]

List Methods

nums = [3, 1, 4, 1, 5]

nums.append(9)          # Add to end
nums.insert(0, 0)       # Insert at index
nums.remove(1)          # Remove first occurrence
nums.pop()              # Remove and return last
nums.sort()             # Sort in place
nums.reverse()          # Reverse in place
nums.extend([7, 8])     # Add multiple elements

List Comprehensions

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

# List comprehension
squares = [i ** 2 for i in range(10)]

# With condition
evens = [i for i in range(20) if i % 2 == 0]

Practice Problems

1. Find second largest element in list
2. Remove duplicates while preserving order
3. Flatten nested lists
4. Find intersection of two lists
5. Implement stack using list