Nested Structures

Real data is often nested.

Examples:

• API JSON
• database records
• configuration files

Nested list (2D list)

matrix = [
  [1, 2, 3],
  [4, 5, 6]
]
print(matrix[0][1])  # 2

Nested dict (JSON style)

user = {
  "id": 101,
  "profile": {"name": "Tom", "city": "Austin"}
}

print(user["profile"]["name"])

Safe access pattern

Use get() to avoid KeyError:

city = user.get("profile", {}).get("city", "Unknown")
print(city)

Loop through nested structures

for row in matrix:
    for value in row:
        print(value)

Graph: nested access

flowchart LR
  A[user] --> B[profile]
  B --> C[name]
  B --> D[city]

Remember

• Nested data is normal in real apps
• Use get() for safe access
• Understand references when nested lists are copied