7.4 Custom Exceptions

Creating our own custom exceptions by inheriting from the Exception class to represent specific application errors.

To make your code more readable and error handling more specific, you can create your own custom exceptions. This is done simply by defining a new class that inherits from Python's built-in `Exception` class. Creating custom exceptions allows you and other programmers to immediately understand what kind of error has occurred, especially in large projects.

# Creating a custom exception
class InvalidAgeError(Exception):
    """Raised when the age is outside the valid range."""
    pass

def check_age_for_entry(age):
    if not 18 <= age <= 100:
        raise InvalidAgeError(f"Age {age} is out of bounds (18-100).")
    print("Age is valid.")

try:
    check_age_for_entry(25) # OK
    check_age_for_entry(15) # Will raise an error
except InvalidAgeError as e:
    print(f"Caught Custom Error: {e}")

Practical Exercises

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7.4 Custom Exceptions

Practical Exercises

Exercise 1:Write a division calculator that asks for two numbers and handles ValueError and ZeroDivisionError with appropriate messages.

Exercise 2:Create a list and a dictionary. Write code that tries to access a non-existent item/key and handles the IndexError and KeyError.

Exercise 3:Create a custom exception InvalidAmountError and a withdrawal function that raises it if the amount is negative or greater than the balance.

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