Exception Types

The standard exception hierarchy. Catch the most specific class that fits — vague except Exception hides bugs.

The big tree

BaseException
 ├── SystemExit
 ├── KeyboardInterrupt
 ├── GeneratorExit
 └── Exception                  ← almost everything you write catches this or a subclass
      ├── ArithmeticError
      │    ├── ZeroDivisionError
      │    ├── OverflowError
      │    └── FloatingPointError
      ├── LookupError
      │    ├── IndexError
      │    └── KeyError
      ├── ValueError
      ├── TypeError
      ├── AttributeError
      ├── ImportError
      │    └── ModuleNotFoundError
      ├── OSError
      │    ├── FileNotFoundError
      │    ├── PermissionError
      │    └── TimeoutError
      ├── RuntimeError
      │    └── RecursionError
      ├── StopIteration
      ├── NameError
      │    └── UnboundLocalError
      └── SyntaxError

The ones you'll catch most

Your own exceptions

class PaymentDeclined(Exception):
    """Raised when the card processor rejects a charge."""

raise PaymentDeclined('Card expired')

Exception groups (3.11+)

try:
    raise ExceptionGroup('multi', [ValueError('a'), TypeError('b')])
except* ValueError as eg:
    print('value:', eg.exceptions)
except* TypeError as eg:
    print('type:', eg.exceptions)

Example

# Common exceptions:
# ValueError, TypeError, KeyError, IndexError,
# FileNotFoundError, ZeroDivisionError, AttributeError,
# StopIteration, ImportError, RuntimeError.
for cls in (ValueError, TypeError, KeyError, IndexError):
    print(cls.__name__)

Exercise

Test yourself