Nested Structures

Nested structures in Python refer to data structures that contain other data structures as their elements. This allows you to represent and work with more complex data.

Nested Lists

A nested list is a list where each element can also be a list.

Example:

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

# Accessing elements
print(matrix[0])       # Output: [1, 2, 3]
print(matrix[0][1])    # Output: 2

Iterating Through Nested Lists:

for row in matrix:
    for element in row:
        print(element, end=" ")
# Output: 1 2 3 4 5 6 7 8 9

Nested Dictionaries

A nested dictionary is a dictionary where values are dictionaries.

Example:

students = {
    "Alice": {"age": 25, "grade": "A"},
    "Bob": {"age": 22, "grade": "B"},
}

# Accessing nested elements
print(students["Alice"]["grade"])  # Output: A

Modifying Nested Dictionaries:

students["Bob"]["grade"] = "A"
print(students["Bob"])  # Output: {'age': 22, 'grade': 'A'}

Iterating Through Nested Dictionaries:

for student, details in students.items():
    print(f"{student}:")
    for key, value in details.items():
        print(f"  {key}: {value}")

Nested Lists and Dictionaries

You can combine lists and dictionaries for complex data structures.

Example:

classroom = [
    {"name": "Alice", "age": 25, "grades": [85, 90, 95]},
    {"name": "Bob", "age": 22, "grades": [80, 85, 88]},
]

# Accessing elements
print(classroom[0]["name"])        # Output: Alice
print(classroom[1]["grades"][2])  # Output: 88

Use Cases of Nested Structures

  1. Matrices and Tables:
    • Nested lists are useful for representing grids or matrices.
    • Example: A chessboard or a 2D table of data.
  2. Hierarchical Data:
    • Nested dictionaries can represent objects with multiple attributes.
    • Example: JSON-like structures.
  3. Combining Data:
    • Use nested lists and dictionaries for more complex data models.
    • Example: Managing data for students, employees, or products.

Example: Representing a Directory

A nested dictionary can represent a file directory:

directory = {
    "Folder1": {
        "File1.txt": "Contents of File1",
        "File2.txt": "Contents of File2",
    },
    "Folder2": {
        "File3.txt": "Contents of File3",
    },
}

print(directory["Folder1"]["File1.txt"])  # Output: Contents of File1

Best Practices for Working with Nested Structures

  1. Clarity: Use meaningful variable names to improve readability.
  2. Access Safely: Use get() to avoid errors when keys are missing in nested dictionaries.
  3. Break Down: When dealing with deeply nested structures, break them into smaller pieces for easier handling.

Practice Exercises

  1. Matrix Operations:
    • Create a 3x3 nested list.
    • Write a function print_diagonal(matrix) to print the diagonal elements.
  2. Student Data:
    • Create a nested dictionary for students with keys "name", "age", and "grades".
    • Add a new student to the dictionary.
  3. Store Inventory:
    • Create a nested dictionary to represent a store’s inventory where:
      • Each key is a category (e.g., "Electronics").
      • Each value is another dictionary containing items and their prices.

Nested structures allow you to represent complex data and provide powerful ways to organize and process information in Python!

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