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

"""

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

Comprehensive Python Guide: Control Structures

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

This program provides an in-depth demonstration of Python's control flow

mechanisms. It covers conditional statements, loops, and error handling,

which are essential for building logic into your programs.

Sections:

1.  Conditional Statements (if, elif, else)

2.  Looping Statements (for, while)

3.  Loop Control Statements (break, continue, pass)

4.  Error Handling (try, except, else, finally)

"""

# 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: CONDITIONAL STATEMENTS (if, elif, else)

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

# These statements allow you to execute code blocks based on certain conditions.

print_header("Conditional Statements")

# --- 1.1: Simple 'if' statement ---

print("\n--- 1.1: Simple 'if' statement ---")

temperature = 35

if temperature > 30:

    print("It's a hot day!")

# --- 1.2: 'if-else' statement ---

print("\n--- 1.2: 'if-else' statement ---")

age = 17

if age >= 18:

    print("You are eligible to vote.")

else:

    print("You are not eligible to vote yet.")

# --- 1.3: 'if-elif-else' chain ---

print("\n--- 1.3: 'if-elif-else' chain ---")

score = 85

if score >= 90:

    grade = "A"

elif score >= 80:

    grade = "B"

elif score >= 70:

    grade = "C"

elif score >= 60:

    grade = "D"

else:

    grade = "F"

print(f"A score of {score} gets you a grade of '{grade}'.")

# --- 1.4: Nested 'if' statements ---

print("\n--- 1.4: Nested 'if' statements ---")

is_citizen = True

age = 20

if is_citizen:

    if age >= 18:

        print("You are a citizen and eligible to vote.")

    else:

        print("You are a citizen but not yet old enough to vote.")

else:

    print("You must be a citizen to vote.")

# --- 1.5: Ternary Operator (Conditional Expression) ---

# A concise way to write a simple if-else statement.

print("\n--- 1.5: Ternary Operator ---")

is_raining = False

weather_status = "Bring an umbrella" if is_raining else "Enjoy the sunshine"

print(f"Weather status: {weather_status}")

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

# SECTION 2: LOOPING STATEMENTS (for, while)

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

# Loops are used to execute a block of code repeatedly.

print_header("Looping Statements")

# --- 2.1: 'for' loop ---

# Used for iterating over a sequence (like a list, tuple, dict, set, or string).

print("\n--- 2.1: 'for' loop ---")

# Iterating over a list

print("Iterating over a list:")

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

for fruit in fruits:

    print(f"- {fruit}")

# Iterating over a string

print("\nIterating over a string:")

for char in "Python":

    print(char, end=" ")

print() # for a new line

# Using the range() function

print("\nIterating with range():")

for i in range(5): # from 0 up to (but not including) 5

    print(f"Number: {i}")

# Using range() with start, stop, and step

print("\nIterating with range(start, stop, step):")

for i in range(2, 11, 2): # from 2 to 10, incrementing by 2

    print(f"Even number: {i}")

# Iterating over dictionary keys

print("\nIterating over dictionary keys:")

my_dict = {"name": "Alice", "age": 30}

for key in my_dict:

    print(f"Key: {key}, Value: {my_dict[key]}")

# Using enumerate() to get both index and value

print("\nIterating with enumerate():")

for index, fruit in enumerate(fruits):

    print(f"Fruit at index {index} is {fruit}")

# --- 2.2: 'while' loop ---

# Repeats a block of code as long as a condition is true.

print("\n--- 2.2: 'while' loop ---")

count = 5

print("Countdown:")

while count > 0:

    print(count)

    count -= 1 # Decrement the counter

print("Blast off!")

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

# SECTION 3: LOOP CONTROL STATEMENTS (break, continue, pass)

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

print_header("Loop Control Statements")

# --- 3.1: 'break' statement ---

# Exits the loop immediately.

print("\n--- 3.1: 'break' statement ---")

print("Finding the number 7 in a list:")

numbers = [1, 5, 12, 7, 9, 20]

for num in numbers:

    print(f"Checking {num}...")

    if num == 7:

        print("Found it! Breaking the loop.")

        break # Exit the loop

print("Loop finished.")

# --- 3.2: 'continue' statement ---

# Skips the rest of the current iteration and moves to the next one.

print("\n--- 3.2: 'continue' statement ---")

print("Printing only even numbers from 1 to 10:")

for i in range(1, 11):

    if i % 2 != 0: # If the number is odd

        continue   # Skip this iteration

    print(f"Even number: {i}")

# --- 3.3: 'pass' statement ---

# Acts as a placeholder. It does nothing.

print("\n--- 3.3: 'pass' statement ---")

# Useful when a statement is required syntactically but you don't want any code to execute.

for i in range(3):

    # TODO: Implement this feature later

    pass # Avoids an IndentationError

print("The 'pass' statement did nothing, as intended.")

# --- 3.4: 'else' clause in loops ---

# The 'else' block executes only if the loop completes normally (i.e., not terminated by a 'break').

print("\n--- 3.4: 'else' clause in loops ---")

print("Searching for a number not in the list:")

for num in [1, 3, 5]:

    if num == 4:

        print("Found 4!")

        break

else: # This will execute because the loop did not break

    print("The number 4 was not found in the list.")

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

# SECTION 4: ERROR HANDLING (try, except, else, finally)

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

# Gracefully handles errors and exceptions that might occur during execution.

print_header("Error Handling")

# --- 4.1: Basic 'try-except' block ---

print("\n--- 4.1: Basic 'try-except' block ---")

try:

    result = 10 / 0

    print(f"Result is {result}")

except ZeroDivisionError:

    print("Error: Cannot divide by zero!")

# --- 4.2: Handling multiple specific exceptions ---

print("\n--- 4.2: Handling multiple exceptions ---")

try:

    # Change the value of 'x' to see different outcomes:

    # x = "hello" # -> will trigger TypeError

    # x = 10      # -> will trigger ValueError (can't convert int to int with base)

    x = "10"    # -> will succeed

    num = int(x)

    print(f"Successfully converted '{x}' to the number {num}.")

except ValueError:

    print(f"Error: Could not convert '{x}' to an integer.")

except TypeError:

    print(f"Error: The input '{x}' is of the wrong type for conversion.")

# --- 4.3: 'else' and 'finally' clauses ---

print("\n--- 4.3: 'else' and 'finally' clauses ---")

try:

    user_input = "5" # Try changing to "abc" or "0"

    number = int(user_input)

    result = 100 / number

except ValueError:

    print("Invalid input: Please enter a number.")

except ZeroDivisionError:

    print("Error: Cannot divide by zero.")

else:

    # This block runs ONLY if the 'try' block completes without any exceptions.

    print(f"The result of 100 / {number} is {result}.")

finally:

    # This block ALWAYS runs, regardless of whether an exception occurred or not.

    print("Execution of the try-except block is complete.")

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

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

print("="*60)