Benutzerdefinierte Ausnahmeklassen

Einführung

Warum benutzerdefinierte Exceptions?

class AppError(Exception):
    pass
raise AppError('something went wrong')

Von Exception erben

class ValidationError(Exception):
    pass
try:
    raise ValidationError('email is invalid')
except ValidationError as e:
    print(e)

Benutzerdefinierte Attribute hinzufügen

class APIError(Exception):
    def __init__(self, status, message):
        self.status = status
        super().__init__(message)
try:
    raise APIError(404, 'Not found')
except APIError as e:
    print(e.status, e)

Exception-Hierarchie

class AppError(Exception): pass
class DBError(AppError): pass
class NetworkError(AppError): pass
try:
    raise DBError('timeout')
except AppError as e:
    print('app error:', e)

Benutzerdefinierte __str__-Methode

class RangeError(ValueError):
    def __init__(self, val, lo, hi):
        self.val, self.lo, self.hi = val, lo, hi
    def __str__(self):
        return f'{self.val} not in [{self.lo}, {self.hi}]'
print(RangeError(15, 0, 10))

Benutzerdefinierte Exceptions auslösen

class InsufficientFundsError(Exception):
    def __init__(self, needed, available):
        super().__init__(f'Need {needed}, have {available}')
def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientFundsError(amount, balance)
    return balance - amount
try:
    withdraw(100, 200)
except InsufficientFundsError as e:
    print(e)

Über die Basisklasse abfangen

class AppError(Exception): pass
class DBError(AppError): pass
try:
    raise DBError('conn failed')
except AppError:
    print('any app error')

Exception mit Kontextmanager

class SuppressValue(Exception): pass
try:
    raise SuppressValue('ignored')
except SuppressValue:
    pass  # suppress silently
print('continued')

Benutzerdefinierte Exceptions dokumentieren

class ConfigError(Exception):
    """Raised when configuration is invalid.
    Attributes:
        key: The invalid config key
    """
    def __init__(self, key, msg):
        super().__init__(msg)
        self.key = key

Bewährte Vorgehensweisen

# Good structure:
class AppError(Exception): pass
class ValidationError(AppError): pass
class NotFoundError(AppError): pass
print('hierarchy demo')

Schnellüberprüfung

Zusammenfassung

Weiter