Raising Custom Exceptions

Sometimes, you need to stop execution deliberately because a condition that makes the program unstable or illogical has been met. The raise statement allows you to trigger an exception manually.

Using raise with Built-in Exceptions

You can raise standard Python exceptions and provide a message explaining why.

python def check_age(age): if not isinstance(age, int): raise TypeError("Age must be an integer.") if age < 0: raise ValueError("Age cannot be negative.") print("Age check passed.")

try: check_age(-5) except ValueError as e: print(f"Error caught: {e}")

Output: Error caught: Age cannot be negative.

When to Raise an Exception

• When a function receives invalid arguments (like the check_age example).
• When required external resources (like files or network connections) are unavailable.
• When logic fails spectacularly (e.g., data corruption detected).

Raising exceptions is crucial for creating robust functions that clearly signal failure states to the calling code.