📋 Lists and Indexing — Ordered Collections

Lists store multiple items in a specific order, and you access them using their position (index).

🎯 Creating Lists

A list is a collection of items enclosed in square brackets, separated by commas. Order matters!

# Empty list
empty_list = []

# List of numbers
numbers = [10, 20, 30, 40, 50]

# List of strings
colors = ["red", "green", "blue"]

# Mixed data types
mixed = [1, "hello", 3.14, True]

💡 Understanding Indexing

Python uses zero-based indexing—the first item is at position 0, not 1. You access items using square brackets with the index.

fruits = ["apple", "banana", "orange", "grape"]

print(fruits[0])   # apple (first item)
print(fruits[1])   # banana (second item)
print(fruits[3])   # grape (fourth item)
print(fruits[-1])  # grape (last item, negative index)
print(fruits[-2])  # orange (second from last)

🎨 Real-World Example: Grade Tracking

# Student's test scores in order
grades = [85, 92, 78, 88, 95]

# Access specific grades
first_test = grades[0]  # 85
last_test = grades[-1]  # 95

# Find average
average = sum(grades) / len(grades)
print(f"Average: {average}")  # Average: 87.6

📊 Indexing Visualization

fruits = ["apple", "banana", "orange", "grape"]

Index:     0         1          2         3
          ↓         ↓          ↓         ↓
List:   apple    banana     orange    grape
          ↑         ↑          ↑         ↑
Negative: -4       -3         -2       -1

🔑 Key Takeaways

• ✅ Lists store ordered items in square brackets

• ✅ Indexing starts at 0 (not 1)

• ✅ Negative indices count from the end

• ✅ Use `len()` to find the number of items

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