Chapter 10: Error Handling

# NameError - using a variable that doesn't exist
print(my_score)

# TypeError - trying to add a string and a number
result = "Age: " + 15
print(result)

# ZeroDivisionError - dividing by zero
answer = 100 / 0
print(answer)

# Without try/except, this would crash!
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Can't divide by zero!")

print("Program keeps running!")

# A practical example: safely converting user input
user_input = "hello"  # Imagine the user typed this

try:
    number = int(user_input)
    print("You entered:", number)
except ValueError:
    print("That's not a valid number!")
    print("You typed:", user_input)

# Handling different errors differently
def divide(a, b):
    try:
        result = a / b
        print("Result:", result)
    except ZeroDivisionError:
        print("Error: You can't divide by zero!")
    except TypeError:
        print("Error: Both values must be numbers!")
    finally:
        print("--- Calculation attempt finished ---")

print("Test 1: Normal division")
divide(10, 3)
print()
print("Test 2: Division by zero")
divide(10, 0)
print()
print("Test 3: Wrong type")
divide("ten", 2)

# Simulating an input validation loop
user_attempts = ["abc", "twelve", "3.5", "7"]
attempt_index = 0
valid_number = None

while valid_number is None:
    user_input = user_attempts[attempt_index]
    print(f"User types: '{user_input}'")
    attempt_index += 1
    try:
        valid_number = int(user_input)
        print(f"Valid! The number is {valid_number}")
    except ValueError:
        print("That's not a whole number. Please try again.\n")

print(f"\nSuccessfully got a valid number after {attempt_index} attempt(s).")

# Capturing the error message with 'as'
test_values = ["42", "hello", "3.14", "", "99"]

for value in test_values:
    try:
        number = int(value)
        print(f"'{value}' converted to {number}")
    except ValueError as e:
        print(f"'{value}' failed: {e}")

print("\nAll values processed!")

# Raising your own errors for custom validation
def set_age(age):
    if not isinstance(age, int):
        raise TypeError("Age must be a whole number")
    if age < 0:
        raise ValueError("Age must be positive")
    if age > 150:
        raise ValueError("Age cannot be greater than 150")
    print(f"Age set to {age}")

# Test with various inputs
test_ages = [25, -3, 200, "twenty", 0, 150]

for age in test_ages:
    try:
        set_age(age)
    except (ValueError, TypeError) as e:
        print(f"Invalid age '{age}': {e}")

def validate_score(value):
    """Validate that a test score is an integer between 0 and 100."""
    try:
        score = int(value)
    except (ValueError, TypeError):
        return f"REJECTED '{value}': not a valid whole number"
    if score < 0:
        return f"REJECTED {score}: score cannot be negative"
    if score > 100:
        return f"REJECTED {score}: score cannot exceed 100"
    return f"ACCEPTED: {score} is a valid score"

# --- Normal test data ---
print("=== Normal Data ===")
print(validate_score(55))
print(validate_score(73))

# --- Boundary test data ---
print("\n=== Boundary Data ===")
print(validate_score(0))     # Lower boundary
print(validate_score(100))   # Upper boundary
print(validate_score(-1))    # Just below
print(validate_score(101))   # Just above

# --- Erroneous test data ---
print("\n=== Erroneous Data ===")
print(validate_score("abc"))
print(validate_score(""))
print(validate_score(-500))
print(validate_score(999))