🧩 Custom Exceptions¶

Custom exceptions let you describe errors in your own domain language. Instead of raising generic errors, you can create meaningful types that make debugging and handling clearer.

✅ Why Create Custom Exceptions?¶

Clarity: InvalidEmailError is more meaningful than ValueError.
Control: Callers can catch specific error types.
Structure: You can build an error hierarchy.

✅ Defining a Custom Exception¶

class InvalidEmailError(ValueError):
    pass


def register(email):
    if "@" not in email:
        raise InvalidEmailError("Email must contain '@'")

✅ Exception Hierarchies¶

class PaymentError(Exception):
    pass


class CardDeclinedError(PaymentError):
    pass


class InsufficientFundsError(PaymentError):
    pass

Catch a whole category or a specific subtype:

try:
    charge(card)
except CardDeclinedError:
    handle_decline()
except PaymentError:
    handle_generic_payment_error()

🔍 Key Takeaways¶

Custom exceptions improve readability and handling.
Inherit from a built-in exception when appropriate.
Use hierarchies for related error types.

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