# -*- coding: utf-8 -*-

"""

================================================================================

Comprehensive Python Guide: Data Structures

================================================================================

This program provides an in-depth demonstration of Python's core data

structures: Lists, Tuples, Dictionaries, and Sets.

It illustrates their creation, common operations, and key characteristics,

such as mutability (can be changed) vs. immutability (cannot be changed).

Sections:

1.  Lists       (Mutable, Ordered)

2.  Tuples      (Immutable, Ordered)

3.  Dictionaries(Mutable, Key-Value Pairs, Ordered in Python 3.7+)

4.  Sets        (Mutable, Unordered, Unique Elements)

"""

# A function to print section headers for better readability.

def print_header(title):

    """Prints a formatted header to the console."""

    print("\n" + "="*60)

    print(f"| {title.center(56)} |")

    print("="*60)

# ==============================================================================

# SECTION 1: LISTS (Mutable, Ordered)

# ==============================================================================

# A list is a collection which is ordered and changeable. Allows duplicate members.

print_header("Lists [Mutable, Ordered]")

# --- 1.1: Creation and Accessing ---

fruits = ["apple", "banana", "cherry", "orange", "kiwi"]

print(f"Initial list: {fruits}")

print(f"First element (index 0): {fruits[0]}")

print(f"Last element (index -1): {fruits[-1]}")

print(f"Slice from index 1 to 3: {fruits[1:3]}") # Elements at index 1 and 2

# --- 1.2: Modifying a List (Mutability) ---

print("\n--- Modifying the list (demonstrates mutability) ---")

fruits[1] = "blackberry" # Change an item

print(f"After changing index 1: {fruits}")

fruits.append("mango") # Add an item to the end

print(f"After appending 'mango': {fruits}")

fruits.insert(2, "strawberry") # Insert an item at a specific position

print(f"After inserting 'strawberry' at index 2: {fruits}")

removed_fruit = fruits.pop(3) # Remove and return item at index 3

print(f"After popping index 3 ('{removed_fruit}'): {fruits}")

fruits.remove("apple") # Remove the first occurrence of a value

print(f"After removing 'apple': {fruits}")

# --- 1.3: List Methods ---

print("\n--- Common list methods ---")

numbers = [5, 1, 9, 3, 7]

print(f"Original numbers list: {numbers}")

numbers.sort()

print(f"Sorted list (in-place): {numbers}")

numbers.reverse()

print(f"Reversed list (in-place): {numbers}")

print(f"Length of the fruits list: {len(fruits)}")

# ==============================================================================

# SECTION 2: TUPLES (Immutable, Ordered)

# ==============================================================================

# A tuple is a collection which is ordered and unchangeable. Allows duplicate members.

print_header("Tuples (Immutable, Ordered)")

# --- 2.1: Creation and Accessing ---

point = (10, 20, 30)

print(f"Initial tuple: {point}")

print(f"Element at index 0: {point[0]}")

print(f"Slice of the last two elements: {point[-2:]}")

# --- 2.2: Immutability ---

print("\n--- Demonstrating immutability ---")

print("Trying to change a tuple element will raise a TypeError.")

# The following line is commented out because it would stop the program.

# point[0] = 5  # <-- This would raise TypeError: 'tuple' object does not support item assignment

# --- 2.3: Tuple Methods & Unpacking ---

print("\n--- Tuple methods and unpacking ---")

mixed_tuple = ('a', 'b', 'c', 'a', 'd')

print(f"Tuple: {mixed_tuple}")

print(f"Count of 'a' in the tuple: {mixed_tuple.count('a')}")

print(f"Index of the first 'c': {mixed_tuple.index('c')}")

# Tuple unpacking

x, y, z = point

print(f"Unpacked tuple: x={x}, y={y}, z={z}")

# ==============================================================================

# SECTION 3: DICTIONARIES (Mutable, Key-Value Pairs)

# ==============================================================================

# A dictionary is a collection which is unordered (in Python < 3.7),

# changeable and indexed by a unique key.

print_header("Dictionaries [Mutable, Key-Value]")

# --- 3.1: Creation and Accessing ---

person = {

    "first_name": "John",

    "last_name": "Doe",

    "age": 30

}

print(f"Initial dictionary: {person}")

print(f"Value for key 'first_name': {person['first_name']}")

# Using .get() is safer as it returns None instead of an error for missing keys

print(f"Value for key 'city' (using .get()): {person.get('city')}")

# --- 3.2: Modifying a Dictionary ---

print("\n--- Modifying the dictionary ---")

person['age'] = 31 # Update a value

print(f"After updating age: {person}")

person['city'] = "New York" # Add a new key-value pair

print(f"After adding city: {person}")

removed_value = person.pop('last_name') # Remove a key-value pair

print(f"After removing 'last_name' ('{removed_value}'): {person}")

# --- 3.3: Iterating over a Dictionary ---

print("\n--- Iterating over the dictionary ---")

print("Keys:")

for key in person.keys():

    print(f"- {key}")

print("\nValues:")

for value in person.values():

    print(f"- {value}")

print("\nItems (key-value pairs):")

for key, value in person.items():

    print(f"- {key}: {value}")

# ==============================================================================

# SECTION 4: SETS (Mutable, Unordered, Unique)

# ==============================================================================

# A set is a collection which is unordered and unindexed. No duplicate members.

print_header("Sets [Mutable, Unordered, Unique]")

# --- 4.1: Creation and Basic Operations ---

# Duplicates are automatically removed

numbers_set = {1, 2, 3, 4, 4, 5, 2}

print(f"Initial set (duplicates removed): {numbers_set}")

numbers_set.add(6)

print(f"After adding 6: {numbers_set}")

numbers_set.remove(3) # Raises an error if the element is not found

print(f"After removing 3: {numbers_set}")

numbers_set.discard(10) # Does not raise an error if element is not found

print(f"After discarding 10 (no error): {numbers_set}")

print(f"Is 5 in the set? {5 in numbers_set}")

# --- 4.2: Set Operations ---

print("\n--- Set operations ---")

set_a = {1, 2, 3, 4}

set_b = {3, 4, 5, 6}

print(f"Set A: {set_a}")

print(f"Set B: {set_b}")

union_set = set_a.union(set_b) # or set_a | set_b

print(f"Union (all elements from both): {union_set}")

intersection_set = set_a.intersection(set_b) # or set_a & set_b

print(f"Intersection (elements in both): {intersection_set}")

difference_set = set_a.difference(set_b) # or set_a - set_b

print(f"Difference (elements in A but not B): {difference_set}")

symmetric_diff_set = set_a.symmetric_difference(set_b) # or set_a ^ set_b

print(f"Symmetric Difference (elements in A or B, but not both): {symmetric_diff_set}")

print("\n" + "="*60)

print("DEMONSTRATION COMPLETE".center(60))

print("="*60)