Tutorial 7: Getting User Input (input())

"""
MULTI-INPUT PARSER
Demonstrates reading and processing multiple inputs on one line
"""

print("=" * 60)
print("MULTI-INPUT PARSER")
print("=" * 60)

print("\nPlease enter three integers separated by spaces.")
print("Example: 5 10 15")

# --- Get input and split ---
user_input = input("\nEnter three integers: ").strip()

# --- Split the input into parts ---
parts = user_input.split()
print(f"\nYou entered {len(parts)} number(s): {parts}")

# --- Check if exactly three numbers were entered ---
if len(parts) != 3:
    print("\n❌ Error: You must enter exactly three numbers.")
    print(f"   You entered {len(parts)} number(s). Please try again.")
else:
    # --- Convert using map(int, ...) ---
    try:
        # Method 1: Using map() to convert all at once
        numbers = list(map(int, parts))
        
        # Alternative: Unpack directly
        # a, b, c = map(int, parts)
        
        # --- Extract individual numbers ---
        a, b, c = numbers
        
        # --- Calculate results ---
        sum_result = a + b + c
        average = sum_result / 3
        product = a * b * c
        
        # --- Display results ---
        print("\n" + "-" * 60)
        print("RESULTS")
        print("-" * 60)
        print(f"Numbers: {a}, {b}, {c}")
        print(f"Sum:     {a} + {b} + {c} = {sum_result}")
        print(f"Average: {sum_result} / 3 = {average:.2f}")
        print(f"Product: {a} × {b} × {c} = {product}")
        print("-" * 60)
        
    except ValueError as e:
        print(f"\n❌ Error: Invalid input. Please enter integers only.")
        print(f"   Details: {e}")

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

Sample Output (Success):

============================================================
MULTI-INPUT PARSER
============================================================

Please enter three integers separated by spaces.
Example: 5 10 15

Enter three integers: 5 10 15

You entered 3 number(s): ['5', '10', '15']

------------------------------------------------------------
RESULTS
------------------------------------------------------------
Numbers: 5, 10, 15
Sum:     5 + 10 + 15 = 30
Average: 30 / 3 = 10.00
Product: 5 × 10 × 15 = 750
------------------------------------------------------------

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

Sample Output (Wrong Number of Inputs):

============================================================
MULTI-INPUT PARSER
============================================================

Please enter three integers separated by spaces.
Example: 5 10 15

Enter three integers: 5 10

You entered 2 number(s): ['5', '10']

❌ Error: You must enter exactly three numbers.
   You entered 2 number(s). Please try again.

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

Sample Output (Invalid Input):

============================================================
MULTI-INPUT PARSER
============================================================

Please enter three integers separated by spaces.
Example: 5 10 15

Enter three integers: 5 abc 15

You entered 3 number(s): ['5', 'abc', '15']

❌ Error: Invalid input. Please enter integers only.
   Details: invalid literal for int() with base 10: 'abc'

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

Explanation:

1. split() – Splits the input string into a list of substrings based on whitespace.

2. len(parts) – Checks how many items were entered.

3. map(int, parts) – Applies int() to each element in the list.

4. list(map(int, parts)) – Converts the map object to a list of integers.

5. Unpacking – a, b, c = numbers assigns each value to a separate variable.

6. Error Handling – try/except catches ValueError if conversion fails.

Alternative Approach (Unpacking Directly):

# Alternative: Unpack directly without creating a list
try:
    a, b, c = map(int, parts)
    # ... rest of code
except ValueError:
    print("Invalid input!")
except ValueError:  # This catches the case where there aren't exactly 3 values
    print("Must enter exactly 3 values!")

"""
PASSWORD VALIDATION LOOP
Demonstrates input validation with attempt limiting
"""

print("=" * 60)
print("PASSWORD VALIDATION")
print("=" * 60)

# --- Define the correct password ---
correct_password = "python123"
max_attempts = 3

print(f"\nYou have {max_attempts} attempts to enter the password.")
print("Type 'quit' to exit.\n")

# --- Basic version: Loop until correct ---
print("\n" + "-" * 60)
print("BASIC VERSION (Infinite until correct)")
print("-" * 60)

attempts = 0

while True:
    password = input("Enter password: ").strip()
    attempts += 1
    
    if password == correct_password:
        print("✅ Access granted!")
        print(f"   You succeeded on attempt {attempts}.")
        break
    else:
        print("❌ Incorrect password. Try again.\n")

print("\n" + "-" * 60)
print("BONUS VERSION (Limited to 3 attempts)")
print("-" * 60)

# --- Bonus: Limited attempts version ---
attempts = 0
max_attempts = 3

while attempts < max_attempts:
    password = input(f"Attempt {attempts + 1}/{max_attempts} - Enter password: ").strip()
    attempts += 1
    
    if password == correct_password:
        print("✅ Access granted!")
        print(f"   You succeeded on attempt {attempts}.")
        break
    else:
        remaining = max_attempts - attempts
        if remaining > 0:
            print(f"❌ Incorrect password. {remaining} attempt(s) remaining.\n")
        else:
            print("❌ Incorrect password. No more attempts.")

# Check if user ran out of attempts
if attempts >= max_attempts and password != correct_password:
    print("\n❌ Too many attempts. Access denied.")
    print("   Please try again later.")

print("\n" + "=" * 60)
print("ENHANCED VERSION (With exit option and feedback)")
print("=" * 60)

# --- Enhanced version with features ---
correct_password = "python123"
max_attempts = 3
attempts = 0

print(f"\nYou have {max_attempts} attempts.")
print("Type 'quit' to exit.\n")

while attempts < max_attempts:
    password = input(f"Attempt {attempts + 1}/{max_attempts} - Enter password: ").strip()
    
    # Allow user to quit
    if password.lower() == 'quit':
        print("❌ Exiting program.")
        break
    
    attempts += 1
    
    if password == correct_password:
        print("✅ Access granted!")
        print(f"   You succeeded on attempt {attempts}.")
        break
    else:
        remaining = max_attempts - attempts
        if remaining > 0:
            # Provide hints (optional)
            print(f"❌ Incorrect password. {remaining} attempt(s) remaining.")
            
            # Optional: Provide a hint based on the input
            if len(password) == 0:
                print("   Hint: You didn't enter anything.")
            elif len(password) < len(correct_password):
                print("   Hint: Too short.")
            elif len(password) > len(correct_password):
                print("   Hint: Too long.")
        else:
            print("❌ Incorrect password. No more attempts.")

if attempts >= max_attempts and password != correct_password and password.lower() != 'quit':
    print("\n❌ Too many failed attempts. Access denied.")
    print(f"   You used all {max_attempts} attempts.")
    print("   Please try again later.")

print("\n" + "=" * 60)
print("KEY TAKEAWAYS")
print("=" * 60)
print("  • Use `while` loops for repeated input validation")
print("  • `strip()` removes leading/trailing spaces")
print("  • `break` exits the loop when valid input is received")
print("  • Track attempts with a counter variable")
print("  • Provide clear feedback to guide the user")
print("  • Consider allowing an exit option (e.g., 'quit')")
print("=" * 60)

Sample Output:

============================================================
PASSWORD VALIDATION
============================================================

You have 3 attempts to enter the password.
Type 'quit' to exit.

------------------------------------------------------------
BASIC VERSION (Infinite until correct)
------------------------------------------------------------
Enter password: hello
❌ Incorrect password. Try again.

Enter password: python123
✅ Access granted!
   You succeeded on attempt 2.

------------------------------------------------------------
BONUS VERSION (Limited to 3 attempts)
------------------------------------------------------------
Attempt 1/3 - Enter password: hello
❌ Incorrect password. 2 attempt(s) remaining.

Attempt 2/3 - Enter password: world
❌ Incorrect password. 1 attempt(s) remaining.

Attempt 3/3 - Enter password: python123
✅ Access granted!
   You succeeded on attempt 3.

============================================================
ENHANCED VERSION (With exit option and feedback)
============================================================

You have 3 attempts.
Type 'quit' to exit.

Attempt 1/3 - Enter password: hi
❌ Incorrect password. 2 attempt(s) remaining.
   Hint: Too short.

Attempt 2/3 - Enter password: 
❌ Incorrect password. 1 attempt(s) remaining.
   Hint: You didn't enter anything.

Attempt 3/3 - Enter password: quit
❌ Exiting program.

============================================================
KEY TAKEAWAYS
============================================================
  • Use `while` loops for repeated input validation
  • `strip()` removes leading/trailing spaces
  • `break` exits the loop when valid input is received
  • Track attempts with a counter variable
  • Provide clear feedback to guide the user
  • Consider allowing an exit option (e.g., 'quit')
============================================================

Explanation:

1. Loop Structure – while True (infinite) or while attempts < max_attempts.

2. strip() – Removes leading/trailing spaces from the password.

3. break – Exits the loop when the correct password is entered.

4. Attempt Counter – Tracks how many times the user has tried.

5. Feedback – Provides clear messages about incorrect passwords and remaining attempts.

6. Exit Option – Allows the user to type "quit" to exit gracefully.

Password Strength Hints (Optional Enhancement):

def check_password_strength(password):
    """Provides feedback on password strength."""
    if len(password) < 8:
        return "Too short (min 8 characters)"
    if not any(c.isdigit() for c in password):
        return "Add at least one digit"
    if not any(c.isupper() for c in password):
        return "Add at least one uppercase letter"
    if not any(c.islower() for c in password):
        return "Add at least one lowercase letter"
    return "Strong password!"

"""
GRADE INPUT WITH VALIDATION
Demonstrates robust input validation and letter grade conversion
"""

import time

print("=" * 60)
print("GRADE INPUT WITH VALIDATION")
print("=" * 60)

print("\nPlease enter a grade between 0 and 100.")
print("Enter 'quit' to exit.\n")

# --- Main validation loop ---
def get_valid_grade():
    """
    Continuously asks the user for a valid grade until one is entered.
    Returns the valid grade as a float.
    """
    while True:
        # Get user input
        user_input = input("Enter grade (0-100): ").strip()
        
        # Check for exit command
        if user_input.lower() == 'quit':
            print("❌ Exiting program.")
            return None
        
        # --- Validate input ---
        try:
            # Convert to float (allows decimal grades)
            grade = float(user_input)
            
            # Check if within valid range
            if 0 <= grade <= 100:
                return grade  # Valid grade found
            else:
                print(f"❌ Error: Grade must be between 0 and 100. Got: {grade}")
                print("   Please try again.\n")
                
        except ValueError:
            print(f"❌ Error: '{user_input}' is not a valid number.")
            print("   Please enter a numeric value.\n")

# --- Letter grade function ---
def get_letter_grade(score):
    """
    Returns the letter grade for a given score.
    """
    if score >= 90:
        return 'A'
    elif score >= 80:
        return 'B'
    elif score >= 70:
        return 'C'
    elif score >= 60:
        return 'D'
    else:
        return 'F'

# --- Main program ---
while True:
    grade = get_valid_grade()
    
    if grade is None:  # User quit
        break
    
    # Convert to letter grade
    letter = get_letter_grade(grade)
    
    # Print result
    print("\n" + "-" * 40)
    print(f"Grade: {grade:.2f}")
    print(f"Letter Grade: {letter}")
    print("-" * 40)
    print()

print("\n" + "=" * 60)
print("ENHANCED VERSION - With Statistics")
print("=" * 60)

# --- Enhanced version with statistics tracking ---
grades_list = []
max_grades = 5

print(f"\nEnter up to {max_grades} grades to analyze.")
print("Type 'done' when finished.\n")

def get_enhanced_grade():
    """Get a grade with additional features."""
    while True:
        user_input = input(f"Grade {len(grades_list) + 1}: ").strip()
        
        if user_input.lower() == 'done':
            return None
        
        try:
            grade = float(user_input)
            if 0 <= grade <= 100:
                return grade
            else:
                print(f"❌ Error: Grade must be between 0 and 100. Got: {grade}")
        except ValueError:
            print(f"❌ Error: '{user_input}' is not a valid number.")

# Collect grades
while len(grades_list) < max_grades:
    grade = get_enhanced_grade()
    
    if grade is None:  # User typed 'done'
        break
    
    grades_list.append(grade)
    letter = get_letter_grade(grade)
    print(f"   → Letter grade: {letter}")

# --- Display statistics ---
if grades_list:
    print("\n" + "-" * 60)
    print("GRADE STATISTICS")
    print("-" * 60)
    
    # Calculate statistics
    total = sum(grades_list)
    average = total / len(grades_list)
    highest = max(grades_list)
    lowest = min(grades_list)
    
    # Display all grades with letter grades
    print("\nGrades entered:")
    for i, grade in enumerate(grades_list, 1):
        letter = get_letter_grade(grade)
        print(f"  Grade {i}: {grade:.2f} → {letter}")
    
    print("\n" + "-" * 40)
    print(f"Number of grades: {len(grades_list)}")
    print(f"Sum: {total:.2f}")
    print(f"Average: {average:.2f}")
    print(f"Highest: {highest:.2f}")
    print(f"Lowest: {lowest:.2f}")
    
    # Grade distribution
    print("\nGrade Distribution:")
    letter_counts = {}
    for grade in grades_list:
        letter = get_letter_grade(grade)
        letter_counts[letter] = letter_counts.get(letter, 0) + 1
    
    for letter in ['A', 'B', 'C', 'D', 'F']:
        count = letter_counts.get(letter, 0)
        percentage = (count / len(grades_list)) * 100
        if count > 0:
            print(f"  {letter}: {count} grade(s) ({percentage:.1f}%)")
        else:
            print(f"  {letter}: 0 grade(s)")

print("\n" + "=" * 60)
print("KEY TAKEAWAYS")
print("=" * 60)
print("  • Use `while True` with `break` for validation loops")
print("  • `strip()` removes extra whitespace")
print("  • `try`/`except` handles non-numeric input")
print("  • Range checking ensures values are within bounds")
print("  • Provide clear, specific error messages")
print("  • Allow users to exit gracefully (e.g., 'quit' or 'done')")
print("  • Use functions to organize reusable code")
print("=" * 60)

Sample Output:

============================================================
GRADE INPUT WITH VALIDATION
============================================================

Please enter a grade between 0 and 100.
Enter 'quit' to exit.

Enter grade (0-100): 95

----------------------------------------
Grade: 95.00
Letter Grade: A
----------------------------------------

Enter grade (0-100): 82

----------------------------------------
Grade: 82.00
Letter Grade: B
----------------------------------------

Enter grade (0-100): abc
❌ Error: 'abc' is not a valid number.
   Please enter a numeric value.

Enter grade (0-100): 150
❌ Error: Grade must be between 0 and 100. Got: 150.0
   Please try again.

Enter grade (0-100): 75

----------------------------------------
Grade: 75.00
Letter Grade: C
----------------------------------------

Enter grade (0-100): quit
❌ Exiting program.

============================================================
ENHANCED VERSION - With Statistics
============================================================

Enter up to 5 grades to analyze.
Type 'done' when finished.

Grade 1: 85
   → Letter grade: B
Grade 2: 92
   → Letter grade: A
Grade 3: 78
   → Letter grade: C
Grade 4: 65
   → Letter grade: D
Grade 5: 95
   → Letter grade: A

------------------------------------------------------------
GRADE STATISTICS
------------------------------------------------------------

Grades entered:
  Grade 1: 85.00 → B
  Grade 2: 92.00 → A
  Grade 3: 78.00 → C
  Grade 4: 65.00 → D
  Grade 5: 95.00 → A

----------------------------------------
Number of grades: 5
Sum: 415.00
Average: 83.00
Highest: 95.00
Lowest: 65.00

Grade Distribution:
  A: 2 grade(s) (40.0%)
  B: 1 grade(s) (20.0%)
  C: 1 grade(s) (20.0%)
  D: 1 grade(s) (20.0%)
  F: 0 grade(s)

============================================================
KEY TAKEAWAYS
============================================================
  • Use `while True` with `break` for validation loops
  • `strip()` removes extra whitespace
  • `try`/`except` handles non-numeric input
  • Range checking ensures values are within bounds
  • Provide clear, specific error messages
  • Allow users to exit gracefully (e.g., 'quit' or 'done')
  • Use functions to organize reusable code
============================================================

Explanation:

Validation Loop Structure:

1. while True – Creates an infinite loop that repeats until valid input is received.

2. strip() – Removes leading/trailing spaces from input.

3. try/except – Catches ValueError when input is not a number.

4. Range Check – Verifies 0 <= grade <= 100.

5. return grade – Exits the function and returns the valid grade.

6. break – Exits the loop when 'quit' is entered.

Letter Grade Function:

• if score >= 90 – Returns 'A'
• elif score >= 80 – Returns 'B'
• elif score >= 70 – Returns 'C'
• elif score >= 60 – Returns 'D'
• else – Returns 'F'

Enhanced Features:

1. Collect Multiple Grades – Stores grades in a list.

2. Statistics – Calculates sum, average, highest, lowest.

3. Grade Distribution – Counts how many of each letter grade.

4. Percentage – Shows what percentage of grades are in each category.

Common Validation Patterns:

# Pattern 1: Simple validation with break
while True:
    input_value = input("Enter a number: ")
    try:
        value = float(input_value)
        if 0 <= value <= 100:
            break
        print("Out of range!")
    except ValueError:
        print("Not a number!")

# Pattern 2: Validation with function
def get_valid_input(prompt, min_val, max_val):
    while True:
        try:
            value = float(input(prompt))
            if min_val <= value <= max_val:
                return value
            print(f"Must be between {min_val} and {max_val}")
        except ValueError:
            print("Must be a number")

# Pattern 3: Validation with count tracking
attempts = 0
max_attempts = 3
while attempts < max_attempts:
    try:
        value = float(input("Enter: "))
        if 0 <= value <= 100:
            break
        attempts += 1
        print(f"{max_attempts - attempts} attempts remaining")
    except ValueError:
        attempts += 1
        print("Invalid input!")

"""
COFFEE SHOP ORDER SYSTEM
Demonstrates input validation, discount application, and tax calculation
"""

print("=" * 60)
print("☕ COFFEE SHOP ORDER SYSTEM")
print("=" * 60)

# --- Constants ---
COFFEE_PRICE = 3.50
PASTRY_PRICE = 2.25
TAX_RATE = 0.07  # 7%
DISCOUNT_CODE = "SAVE10"
DISCOUNT_RATE = 0.10  # 10%

print("\nWelcome to the Coffee Shop!")
print(f"☕ Coffee:  ${COFFEE_PRICE:.2f} each")
print(f"🥐 Pastry: ${PASTRY_PRICE:.2f} each")
print(f"Discount code: '{DISCOUNT_CODE}' for 10% off")
print(f"Sales tax: {TAX_RATE * 100:.0f}%\n")

# --- Helper function for getting integer input ---
def get_integer_input(prompt, item_name):
    """
    Gets an integer input from the user with error handling.
    Returns 0 if invalid input is provided.
    """
    while True:
        try:
            value = int(input(prompt))
            if value < 0:
                print(f"  ⚠️ {item_name} cannot be negative. Using 0.")
                return 0
            return value
        except ValueError:
            print(f"  ❌ Invalid input! Please enter a whole number.")
            print(f"  ⚠️ Setting {item_name} to 0.")
            return 0

# --- Step 1: Get order quantities ---
print("Please enter your order:")

coffee_count = get_integer_input("  Number of coffees: ", "Coffee count")
pastry_count = get_integer_input("  Number of pastries: ", "Pastry count")

# --- Step 2: Calculate subtotal ---
coffee_total = coffee_count * COFFEE_PRICE
pastry_total = pastry_count * PASTRY_PRICE
subtotal = coffee_total + pastry_total

# --- Display order summary ---
print("\n" + "-" * 40)
print("ORDER SUMMARY")
print("-" * 40)
print(f"Coffees:  {coffee_count} × ${COFFEE_PRICE:.2f} = ${coffee_total:>7.2f}")
print(f"Pastries: {pastry_count} × ${PASTRY_PRICE:.2f} = ${pastry_total:>7.2f}")
print("-" * 40)
print(f"Subtotal:                       ${subtotal:>7.2f}")

# --- Step 3: Apply discount if applicable ---
discount = 0.0

if subtotal > 0:
    discount_input = input("\nDo you have a discount code? (Enter code or press Enter): ").strip()
    
    if discount_input.upper() == DISCOUNT_CODE:
        discount = subtotal * DISCOUNT_RATE
        print(f"✅ Discount applied! You saved ${discount:.2f}")
    elif discount_input:
        print(f"❌ Invalid discount code: '{discount_input}'")
    else:
        print("No discount code entered.")
else:
    print("\nNo items ordered. No discount applied.")

# --- Step 4: Calculate total with tax ---
subtotal_after_discount = subtotal - discount
tax = subtotal_after_discount * TAX_RATE
total = subtotal_after_discount + tax

# --- Display final bill ---
print("\n" + "-" * 40)
print("FINAL BILL")
print("-" * 40)

if discount > 0:
    print(f"Subtotal:                       ${subtotal:>7.2f}")
    print(f"Discount (10%):                 -${discount:>6.2f}")
    print(f"Subtotal after discount:         ${subtotal_after_discount:>7.2f}")
else:
    print(f"Subtotal:                       ${subtotal:>7.2f}")

print(f"Tax ({TAX_RATE * 100:.0f}%):                       ${tax:>7.2f}")
print("=" * 40)
print(f"TOTAL:                          ${total:>7.2f}")
print("=" * 40)

# --- Additional information ---
print("\n" + "-" * 40)
print("ORDER DETAILS")
print("-" * 40)
print(f"Items ordered: {coffee_count + pastry_count}")
print(f"Total items:   {coffee_count + pastry_count}")
if coffee_count + pastry_count > 0:
    avg_price = total / (coffee_count + pastry_count)
    print(f"Average price per item: ${avg_price:.2f}")
else:
    print("No items ordered.")

print("\n" + "=" * 60)
print("KEY TAKEAWAYS")
print("=" * 60)
print("  • Use `try`/`except` to validate numeric input")
print("  • Use `.upper()` for case‑insensitive comparisons")
print("  • Calculate percentages with decimal multipliers (0.10 for 10%)")
print("  • Apply tax to the discounted subtotal")
print("  • Format currency with `{value:.2f}` and `>7.2f` for alignment")
print("  • Always handle edge cases (empty input, negative values)")
print("=" * 60)

Sample Output (With Discount):

============================================================
☕ COFFEE SHOP ORDER SYSTEM
============================================================

Welcome to the Coffee Shop!
☕ Coffee:  $3.50 each
🥐 Pastry: $2.25 each
Discount code: 'SAVE10' for 10% off
Sales tax: 7%

Please enter your order:
  Number of coffees: 3
  Number of pastries: 2

----------------------------------------
ORDER SUMMARY
----------------------------------------
Coffees:  3 × $3.50 = $ 10.50
Pastries: 2 × $2.25 = $  4.50
----------------------------------------
Subtotal:                       $ 15.00

Do you have a discount code? (Enter code or press Enter): SAVE10
✅ Discount applied! You saved $1.50

----------------------------------------
FINAL BILL
----------------------------------------
Subtotal:                       $ 15.00
Discount (10%):                 -$  1.50
Subtotal after discount:         $ 13.50
Tax (7%):                       $  0.95
========================================
TOTAL:                          $ 14.45
========================================

----------------------------------------
ORDER DETAILS
----------------------------------------
Items ordered: 5
Total items:   5
Average price per item: $2.89

============================================================
KEY TAKEAWAYS
============================================================
  • Use `try`/`except` to validate numeric input
  • Use `.upper()` for case‑insensitive comparisons
  • Calculate percentages with decimal multipliers (0.10 for 10%)
  • Apply tax to the discounted subtotal
  • Format currency with `{value:.2f}` and `>7.2f` for alignment
  • Always handle edge cases (empty input, negative values)
============================================================

Sample Output (No Discount):

============================================================
☕ COFFEE SHOP ORDER SYSTEM
============================================================

Welcome to the Coffee Shop!
☕ Coffee:  $3.50 each
🥐 Pastry: $2.25 each
Discount code: 'SAVE10' for 10% off
Sales tax: 7%

Please enter your order:
  Number of coffees: 2
  Number of pastries: 1

----------------------------------------
ORDER SUMMARY
----------------------------------------
Coffees:  2 × $3.50 = $  7.00
Pastries: 1 × $2.25 = $  2.25
----------------------------------------
Subtotal:                       $  9.25

Do you have a discount code? (Enter code or press Enter): no

No discount code entered.

----------------------------------------
FINAL BILL
----------------------------------------
Subtotal:                       $  9.25
Tax (7%):                       $  0.65
========================================
TOTAL:                          $  9.90
========================================

----------------------------------------
ORDER DETAILS
----------------------------------------
Items ordered: 3
Total items:   3
Average price per item: $3.30

============================================================
KEY TAKEAWAYS
============================================================
  • Use `try`/`except` to validate numeric input
  • Use `.upper()` for case‑insensitive comparisons
  • Calculate percentages with decimal multipliers (0.10 for 10%)
  • Apply tax to the discounted subtotal
  • Format currency with `{value:.2f}` and `>7.2f` for alignment
  • Always handle edge cases (empty input, negative values)
============================================================

Sample Output (Invalid Input):

============================================================
☕ COFFEE SHOP ORDER SYSTEM
============================================================

Welcome to the Coffee Shop!
☕ Coffee:  $3.50 each
🥐 Pastry: $2.25 each
Discount code: 'SAVE10' for 10% off
Sales tax: 7%

Please enter your order:
  Number of coffees: abc
  ❌ Invalid input! Please enter a whole number.
  ⚠️ Setting Coffee count to 0.
  Number of pastries: -2
  ⚠️ Pastry cannot be negative. Using 0.

----------------------------------------
ORDER SUMMARY
----------------------------------------
Coffees:  0 × $3.50 = $  0.00
Pastries: 0 × $2.25 = $  0.00
----------------------------------------
Subtotal:                       $  0.00

No items ordered. No discount applied.

----------------------------------------
FINAL BILL
----------------------------------------
Subtotal:                       $  0.00
Tax (7%):                       $  0.00
========================================
TOTAL:                          $  0.00
========================================

----------------------------------------
ORDER DETAILS
----------------------------------------
Items ordered: 0
Total items:   0
No items ordered.

============================================================
KEY TAKEAWAYS
============================================================
  • Use `try`/`except` to validate numeric input
  • Use `.upper()` for case‑insensitive comparisons
  • Calculate percentages with decimal multipliers (0.10 for 10%)
  • Apply tax to the discounted subtotal
  • Format currency with `{value:.2f}` and `>7.2f` for alignment
  • Always handle edge cases (empty input, negative values)
============================================================

Explanation:

1. Input Validation – get_integer_input() function uses try/except to handle invalid input.

2. Case‑Insensitive Comparison – discount_input.upper() == DISCOUNT_CODE handles "save10", "Save10", etc.

3. Discount Calculation – discount = subtotal * 0.10

4. Tax Calculation – Tax is applied to the subtotal after discount.

5. Currency Formatting – {value:>7.2f} right‑aligns with 2 decimal places.

6. Edge Cases – Empty input, negative numbers, no order.

"""
EMAIL VALIDATOR
Demonstrates input validation with string methods
"""

print("=" * 60)
print("EMAIL VALIDATOR")
print("=" * 60)

print("\nPlease enter your email address.")
print("Requirements:")
print("  • Must contain '@' symbol")
print("  • Must contain a '.' after the '@'")
print("  • Must not contain spaces")
print("  • Type 'quit' to exit\n")

# --- Main validation function ---
def validate_email(email):
    """
    Validates an email address with basic checks.
    Returns True if valid, False otherwise.
    """
    # Check 1: Not empty
    if not email:
        return False
    
    # Check 2: No spaces (bonus)
    if ' ' in email:
        return False
    
    # Check 3: Must contain '@'
    if '@' not in email:
        return False
    
    # Check 4: Must contain a '.' after the '@'
    at_index = email.index('@')
    if '.' not in email[at_index:]:
        return False
    
    # Check 5: '@' shouldn't be the first character
    if at_index == 0:
        return False
    
    # Check 6: Dot shouldn't be the last character
    if email.endswith('.'):
        return False
    
    # All checks passed!
    return True

# --- Main loop ---
attempts = 0
max_attempts = 5

while attempts < max_attempts:
    email = input(f"Attempt {attempts + 1}/{max_attempts} - Enter email: ").strip()
    attempts += 1
    
    # Check for exit
    if email.lower() == 'quit':
        print("\n❌ Exiting program.")
        break
    
    # Validate the email
    if validate_email(email):
        print("✅ Email accepted!")
        print(f"   Email: {email}")
        break
    else:
        print("❌ Invalid email address.")
        # Provide specific feedback
        if not email:
            print("   - Email cannot be empty.")
        elif ' ' in email:
            print("   - Email cannot contain spaces.")
        elif '@' not in email:
            print("   - Email must contain an '@' symbol.")
        elif email.index('@') == 0:
            print("   - Email must have text before the '@'.")
        elif '.' not in email[email.index('@'):]:
            print("   - Email must contain a '.' after the '@'.")
        elif email.endswith('.'):
            print("   - Email cannot end with a '.'.")
        else:
            print("   - Please check the format.")
        
        remaining = max_attempts - attempts
        if remaining > 0:
            print(f"   {remaining} attempt(s) remaining.\n")
        else:
            print("   No more attempts left.\n")

if attempts >= max_attempts and not validate_email(email) and email.lower() != 'quit':
    print("\n❌ Too many invalid attempts. Please try again later.")

print("\n" + "=" * 60)
print("ENHANCED VERSION - With More Validations")
print("=" * 60)

# --- Enhanced version with additional validations ---
def validate_email_enhanced(email):
    """
    Enhanced email validation with more checks.
    """
    # Basic checks
    if not validate_email(email):
        return False, "Basic validation failed"
    
    # Check: Must have at least one character before '@'
    at_index = email.index('@')
    if at_index < 1:
        return False, "Must have text before '@'"
    
    # Check: Must have at least 2 characters after '@' before dot
    domain_part = email[at_index + 1:]
    if '.' in domain_part:
        dot_index = domain_part.index('.')
        if dot_index < 1:
            return False, "Must have text between '@' and '.'"
    else:
        return False, "Must contain '.' after '@'"
    
    # Check: Domain extension should be at least 2 characters
    after_dot = domain_part[domain_part.index('.') + 1:]
    if len(after_dot) < 2:
        return False, "Domain extension must be at least 2 characters"
    
    # Check: No multiple '@' symbols
    if email.count('@') > 1:
        return False, "Multiple '@' symbols found"
    
    return True, "Valid email"

# --- Interactive enhanced version ---
print("\nEnhanced validation with more checks:\n")

while True:
    email = input("Enter email (or 'quit'): ").strip()
    
    if email.lower() == 'quit':
        print("Exiting.")
        break
    
    is_valid, message = validate_email_enhanced(email)
    
    if is_valid:
        print(f"✅ {message}")
        print(f"   Email: {email}")
        
        # Extract parts
        at_index = email.index('@')
        username = email[:at_index]
        domain = email[at_index + 1:]
        print(f"   Username: {username}")
        print(f"   Domain: {domain}")
        break
    else:
        print(f"❌ Invalid: {message}")

print("\n" + "=" * 60)
print("KEY TAKEAWAYS")
print("=" * 60)
print("  • Use `strip()` to remove whitespace")
print("  • Use `'@' in email` to check for character presence")
print("  • Use `email.index('@')` to find the position of a character")
print("  • Use slicing `email[at_index:]` to check after a position")
print("  • Use `email.endswith('.')` to check the ending")
print("  • Provide specific error messages for better user experience")
print("  • Basic validation is better than no validation!")
print("=" * 60)

Sample Output:

============================================================
EMAIL VALIDATOR
============================================================

Please enter your email address.
Requirements:
  • Must contain '@' symbol
  • Must contain a '.' after the '@'
  • Must not contain spaces
  • Type 'quit' to exit

Attempt 1/5 - Enter email: alice@emailcom
❌ Invalid email address.
   - Email must contain a '.' after the '@'.
   4 attempt(s) remaining.

Attempt 2/5 - Enter email: alice@.com
❌ Invalid email address.
   - Email must contain a '.' after the '@'.
   3 attempt(s) remaining.

Attempt 3/5 - Enter email: alice email@.com
❌ Invalid email address.
   - Email cannot contain spaces.
   2 attempt(s) remaining.

Attempt 4/5 - Enter email: alice@email.com
✅ Email accepted!
   Email: alice@email.com

============================================================
ENHANCED VERSION - With More Validations
============================================================

Enhanced validation with more checks:

Enter email (or 'quit'): alice@email.com
✅ Valid email
   Email: alice@email.com
   Username: alice
   Domain: email.com

============================================================
KEY TAKEAWAYS
============================================================
  • Use `strip()` to remove whitespace
  • Use `'@' in email` to check for character presence
  • Use `email.index('@')` to find the position of a character
  • Use slicing `email[at_index:]` to check after a position
  • Use `email.endswith('.')` to check the ending
  • Provide specific error messages for better user experience
  • Basic validation is better than no validation!
============================================================

Explanation:

Basic Validation Checks:

1. Not Empty – if not email: return False

2. No Spaces – if ' ' in email: return False

3. Contains '@' – if '@' not in email: return False

4. Dot After '@' – if '.' not in email[at_index:]: return False

5. Text Before '@' – if at_index == 0: return False

6. Not Ending with Dot – if email.endswith('.'): return False

Enhanced Validation Checks:

1. Multiple '@' – if email.count('@') > 1: return False

2. Text Between '@' and '.' – Check that domain part has content.

3. Domain Extension Length – At least 2 characters (e.g., ".com", ".org").

4. Username Length – At least 1 character before '@'.

String Methods Used:

• strip() – Removes whitespace.
• in – Checks membership (contains '@').
• index() – Finds position of a character.
• count() – Counts occurrences.
• endswith() – Checks the ending.
• Slicing – email[at_index:] gets the part after '@'.

Simple vs. Full Validation:

This program provides basic validation (enough for learning). Real email validation is much more complex and typically uses regular expressions:

import re
def validate_email_regex(email):
    pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
    return bool(re.match(pattern, email))

"""
INTERACTIVE MENU CALCULATOR
Demonstrates menu-driven program with error handling
"""

import math

print("=" * 60)
print("🖩 INTERACTIVE MENU CALCULATOR")
print("=" * 60)

# --- Helper functions for arithmetic operations ---
def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b

def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero!")
    return a / b

# --- Helper function to get a number from user ---
def get_number(prompt):
    """
    Gets a valid number from the user.
    Returns the number as a float.
    """
    while True:
        try:
            return float(input(prompt))
        except ValueError:
            print("  ❌ Invalid input! Please enter a number.")
            print("  Try again.\n")

# --- Helper function to get menu choice ---
def get_menu_choice():
    """
    Gets a valid menu choice from the user.
    Returns the choice as an integer.
    """
    while True:
        try:
            choice = int(input("\nEnter your choice (1-5): ").strip())
            if 1 <= choice <= 5:
                return choice
            else:
                print("  ❌ Invalid choice! Please enter a number between 1 and 5.")
                print("  Try again.")
        except ValueError:
            print("  ❌ Invalid input! Please enter a number.")
            print("  Try again.")

# --- Main program loop ---
def main():
    """
    Main program loop for the interactive calculator.
    """
    while True:
        # Display the menu
        print("\n" + "=" * 50)
        print("            MENU")
        print("=" * 50)
        print("  1. Add two numbers")
        print("  2. Subtract two numbers")
        print("  3. Multiply two numbers")
        print("  4. Divide two numbers")
        print("  5. Exit")
        print("=" * 50)
        
        # Get user choice
        choice = get_menu_choice()
        
        # Handle exit
        if choice == 5:
            print("\n👋 Thank you for using the calculator. Goodbye!")
            break
        
        # --- Get two numbers ---
        print("\n" + "-" * 40)
        print(f"OPERATION: {['', 'Addition', 'Subtraction', 'Multiplication', 'Division'][choice]}")
        print("-" * 40)
        
        num1 = get_number("Enter first number: ")
        num2 = get_number("Enter second number: ")
        
        # --- Perform the operation ---
        operation_names = ['', 'Adding', 'Subtracting', 'Multiplying', 'Dividing']
        
        try:
            if choice == 1:
                result = add(num1, num2)
                symbol = '+'
            elif choice == 2:
                result = subtract(num1, num2)
                symbol = '-'
            elif choice == 3:
                result = multiply(num1, num2)
                symbol = '×'
            elif choice == 4:
                result = divide(num1, num2)
                symbol = '÷'
            
            # Display result
            print("\n" + "-" * 40)
            print("RESULT")
            print("-" * 40)
            print(f"  {num1} {symbol} {num2} = {result}")
            print("-" * 40)
            
        except ValueError as e:
            print(f"\n❌ Error: {e}")
            print("   Please try again.\n")
        except Exception as e:
            print(f"\n❌ An unexpected error occurred: {e}")

# --- Run the program ---
if __name__ == "__main__":
    main()

print("\n" + "=" * 60)
print("ENHANCED VERSION - With History and More Features")
print("=" * 60)

# --- Enhanced version with calculation history ---
def enhanced_calculator():
    """
    Enhanced calculator with history tracking and more features.
    """
    history = []
    calculation_count = 0
    
    def add_to_history(operation, num1, num2, result):
        """Adds a calculation to the history."""
        history.append({
            'operation': operation,
            'num1': num1,
            'num2': num2,
            'result': result
        })
    
    while True:
        # Display menu with history count
        print("\n" + "=" * 50)
        print("        ENHANCED CALCULATOR")
        print("=" * 50)
        print("  1. Add two numbers")
        print("  2. Subtract two numbers")
        print("  3. Multiply two numbers")
        print("  4. Divide two numbers")
        print("  5. View History")
        print("  6. Clear History")
        print("  7. Exit")
        print("=" * 50)
        print(f"Total calculations: {calculation_count}")
        
        # Get choice
        try:
            choice = int(input("\nEnter your choice (1-7): ").strip())
        except ValueError:
            print("❌ Invalid input! Please enter a number.")
            continue
        
        # Handle choices
        if choice == 7:
            print("\n👋 Thank you! Goodbye!")
            break
        
        elif choice == 5:
            # View history
            if not history:
                print("\n📋 No calculations in history.")
            else:
                print("\n" + "-" * 40)
                print("CALCULATION HISTORY")
                print("-" * 40)
                for i, entry in enumerate(history, 1):
                    operation = entry['operation']
                    num1 = entry['num1']
                    num2 = entry['num2']
                    result = entry['result']
                    print(f"  {i}. {num1} {operation} {num2} = {result}")
                print("-" * 40)
            continue
        
        elif choice == 6:
            # Clear history
            history = []
            calculation_count = 0
            print("\n🗑️ History cleared!")
            continue
        
        elif choice not in [1, 2, 3, 4]:
            print("❌ Invalid choice! Please select 1-7.")
            continue
        
        # --- Get numbers and perform calculation ---
        print("\n" + "-" * 40)
        operation_names = ['', 'Addition', 'Subtraction', 'Multiplication', 'Division']
        print(f"OPERATION: {operation_names[choice]}")
        print("-" * 40)
        
        try:
            num1 = float(input("Enter first number: "))
            num2 = float(input("Enter second number: "))
        except ValueError:
            print("❌ Invalid input! Please enter numbers.")
            continue
        
        # Perform operation
        try:
            if choice == 1:
                result = num1 + num2
                symbol = '+'
                op_name = 'addition'
            elif choice == 2:
                result = num1 - num2
                symbol = '-'
                op_name = 'subtraction'
            elif choice == 3:
                result = num1 * num2
                symbol = '×'
                op_name = 'multiplication'
            elif choice == 4:
                if num2 == 0:
                    print("\n❌ Error: Cannot divide by zero!")
                    continue
                result = num1 / num2
                symbol = '÷'
                op_name = 'division'
            
            # Store in history
            add_to_history(symbol, num1, num2, result)
            calculation_count += 1
            
            # Display result
            print("\n" + "-" * 40)
            print(f"Result: {num1} {symbol} {num2} = {result}")
            print("-" * 40)
            
            # Optional: Additional statistics
            print(f"\n  Calculation #{calculation_count}")
            print(f"  Operation: {op_name.title()}")
            if choice == 4:
                print(f"  Quotient: {num1 / num2}")
                print(f"  Remainder: {num1 % num2}")
            
        except Exception as e:
            print(f"\n❌ Error: {e}")

# Uncomment to run enhanced version
# enhanced_calculator()

print("\n" + "=" * 60)
print("KEY TAKEAWAYS")
print("=" * 60)
print("  • Use `while True` with `break` for menu loops")
print("  • Use functions to organize code")
print("  • Validate menu choices with range checking")
print("  • Use `try`/`except` for number conversion")
print("  • Use `try`/`except` for division by zero")
print("  • Provide clear feedback for all inputs")
print("  • Consider adding history for better usability")
print("=" * 60)

Sample Output:

============================================================
🖩 INTERACTIVE MENU CALCULATOR
============================================================

==================================================
            MENU
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. Exit
==================================================

Enter your choice (1-5): 1

----------------------------------------
OPERATION: Addition
----------------------------------------
Enter first number: 15
Enter second number: 10

----------------------------------------
RESULT
----------------------------------------
  15.0 + 10.0 = 25.0
----------------------------------------

==================================================
            MENU
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. Exit
==================================================

Enter your choice (1-5): 4

----------------------------------------
OPERATION: Division
----------------------------------------
Enter first number: 10
Enter second number: 0

❌ Error: Cannot divide by zero!
   Please try again.

==================================================
            MENU
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. Exit
==================================================

Enter your choice (1-5): 4

----------------------------------------
OPERATION: Division
----------------------------------------
Enter first number: 10
Enter second number: 3

----------------------------------------
RESULT
----------------------------------------
  10.0 ÷ 3.0 = 3.3333333333333335
----------------------------------------

==================================================
            MENU
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. Exit
==================================================

Enter your choice (1-5): 5

👋 Thank you for using the calculator. Goodbye!

============================================================
ENHANCED VERSION - With History and More Features
============================================================

==================================================
        ENHANCED CALCULATOR
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. View History
  6. Clear History
  7. Exit
==================================================
Total calculations: 0

Enter your choice (1-7): 1

----------------------------------------
OPERATION: Addition
----------------------------------------
Enter first number: 100
Enter second number: 50

----------------------------------------
Result: 100.0 + 50.0 = 150.0
----------------------------------------

  Calculation #1
  Operation: Addition

==================================================
        ENHANCED CALCULATOR
==================================================
  1. Add two numbers
  2. Subtract two numbers
  3. Multiply two numbers
  4. Divide two numbers
  5. View History
  6. Clear History
  7. Exit
==================================================
Total calculations: 1

Enter your choice (1-7): 5

----------------------------------------
CALCULATION HISTORY
----------------------------------------
  1. 100.0 + 50.0 = 150.0
----------------------------------------

Explanation:

Menu Structure:

1. Display Menu – Shows options to the user.
2. Get Choice – Validates input is a number between 1-5.
3. Process Choice – Calls appropriate function or exits.
4. Get Numbers – Asks for two numbers with validation.
5. Perform Operation – Calculates and displays result.
6. Loop – Returns to menu until exit.

Error Handling:

1. Invalid Menu Choice – Handles numbers outside 1-5.
2. Invalid Number Input – Catches ValueError from float().
3. Division by Zero – Checks and handles with try/except.

Enhanced Features:

1. Calculation History – Stores all calculations in a list.
2. History Display – Shows all past calculations.
3. Clear History – Resets the history.
4. Calculation Counter – Tracks total calculations.

Menu Choice Validation Patterns:

# Pattern 1: Simple validation
while True:
    choice = input("Enter choice: ")
    if choice in ['1', '2', '3', '4', '5']:
        choice = int(choice)
        break
    print("Invalid choice!")

# Pattern 2: Try/except with range
while True:
    try:
        choice = int(input("Enter choice: "))
        if 1 <= choice <= 5:
            break
        print("Choice must be 1-5")
    except ValueError:
        print("Must enter a number")

Operation Execution Patterns:

# Pattern 1: If-elif-else
if choice == 1:
    result = num1 + num2
elif choice == 2:
    result = num1 - num2
elif choice == 3:
    result = num1 * num2
elif choice == 4:
    result = num1 / num2

# Pattern 2: Using a dictionary (advanced)
operations = {
    1: lambda a, b: a + b,
    2: lambda a, b: a - b,
    3: lambda a, b: a * b,
    4: lambda a, b: a / b
}
result = operations[choice](num1, num2)