🔁 Learn advanced looping techniques in Python, including the for...else and while...else constructs, and how to emulate the classic do...while loop using standard Python syntax.

This section is designed to help you write more expressive and robust loops by understanding how to control execution flow beyond basic iteration.

• ✅ How to use for...else and while...else statements
• 🔁 How to emulate a do...while loop in Python
• 📌 Use cases and best practices for each construct
• 💡 Hidden tips and notes that improve readability and avoid common mistakes

Python allows the else clause to be used with the for loop — this is not available in most other programming languages.

🔹 Syntax:

for item in iterable:
    # code to process item
    if condition:
        break
else:
    # code to run if loop completes normally (no break)

🔸 The else block runs only if the loop completes all iterations without encountering a break statement.

fruits = ['apple', 'banana', 'cherry']
search = 'mango'

for fruit in fruits:
    if fruit == search:
        print(f"Found {search}!")
        break
else:
    print(f"{search} not found.")

🔹 Use Cases:

• Searching for an item in a collection
• Validating input or data before proceeding
• Checking conditions across an entire sequence

Just like for, the while loop can also have an else clause.

🔹 Syntax:

while condition:
    # code to execute while condition is True
    if some_condition:
        break
else:
    # code to run if loop exits because condition became False

🔸 The else block runs if the loop exited due to the condition becoming False, not from a break.

attempts = 0
max_attempts = 3

while attempts < max_attempts:
    password = input("Enter password: ")
    if password == "secret":
        print("Login successful!")
        break
    print("Incorrect password.")
    attempts += 1
else:
    print("Account locked due to too many failed attempts.")

🔹 Use Cases:

• Retry logic with limits
• Game loops
• Input validation with retries

Unlike languages like Java or C++, Python does not have a built-in do...while loop, but you can emulate it using a while loop with a break.

🔹 Concept: The do...while loop executes the body at least once, then checks the condition at the end of each iteration.

import random

MIN, MAX = 1, 10
secret_number = random.randint(MIN, MAX)

while True:
    guess = int(input(f"Guess a number between {MIN} and {MAX}: "))
    
    if guess > secret_number:
        print("Too high. Try again.")
    elif guess < secret_number:
        print("Too low. Try again.")
    else:
        print("Bingo! You guessed it!")
        break

🔹 This pattern ensures the user makes at least one guess before checking whether to continue.

• Use while True to simulate the “do” part.
• Add a break when the exit condition is met.
• Ideal for scenarios where the loop must run at least once.

• 🔁 The else block in both for and while loops runs only when the loop completes naturally — not when interrupted by break, return, or exceptions.
• ❗ Avoid putting complex logic inside the else block unless necessary — it can reduce readability.
• 🧪 The else clause is often misunderstood and underused — but very useful in scenarios where you want to handle a “none found” or “loop completed” case.
• 🚫 Using continue does not affect the else clause — only break does.
• 🧹 Always test edge cases — especially when working with empty iterables in for...else.

def is_prime(n):
    if n <= 1:
        return False
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:
            print(f"{n} is divisible by {i}. Not a prime.")
            break
    else:
        print(f"{n} is a prime number.")
        return True
    return False

is_prime(17)

🎉 Congratulations! You now have a solid understanding of advanced loop structures in Python, including how to use for...else, while...else, and emulate do...while behavior.

Next up: 📦 Section 10: More on Python Functions – learn about unpacking tuples, variable arguments (*args, **kwargs), partial functions, and type hints.