Nested Data Structures

# List of lists (2D grid)
grid = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]
print(grid[1][2])  # 6 (row 1, col 2)

# List of dictionaries (common pattern!)
students = [
    {"name": "Alice", "age": 20, "grades": [85, 90, 78]},
    {"name": "Bob", "age": 22, "grades": [92, 88, 95]},
    {"name": "Charlie", "age": 21, "grades": [70, 75, 80]},
]

for student in students:
    avg = sum(student["grades"]) / len(student["grades"])
    print(f"{student['name']}: avg = {avg:.1f}")

# Dictionary of lists
inventory = {
    "fruits": ["apple", "banana", "cherry"],
    "vegetables": ["carrot", "potato", "tomato"],
    "dairy": ["milk", "cheese", "yogurt"],
}

for category, items in inventory.items():
    print(f"\n{category.upper()}: {', '.join(items)}")

# Nested list comprehension
matrix = [[i * j for j in range(1, 4)] for i in range(1, 4)]
for row in matrix:
    print(row)  # [1,2,3], [2,4,6], [3,6,9]