Exception Handling

Python has a number of keywords associated with exception handling:

• try → block of code to test.
• except → block of code that runs if an error occurs.
• else → runs if no exception occurs.
• finally → always runs (cleanup code, e.g., close file).
• raise → manually raise an exception.

Catching Exceptions

Catch specific exceptions:

Catch multiple:

Catch all (not recommended unless logging/debugging):

Raising Exceptions

Built-in Exceptions

Base Classes:

• BaseException → root of all exceptions.
• Exception → base for most user errors.
• ArithmeticError → base for numeric errors.
• LookupError → base for indexing/key errors.

Common Everyday Exceptions:

• Exception → generic base exception.
• ValueError → invalid value (e.g., int("abc")).
• TypeError → wrong type (e.g., 3 + "hi").
• NameError → variable not defined.
• IndexError → list index out of range.
• KeyError → dict key not found.
• ZeroDivisionError → divide by zero.
• AttributeError → attribute doesn’t exist.
• FileNotFoundError → missing file.
• IOError → I/O error (alias of OSError).
• ImportError → module can’t be imported.
• ModuleNotFoundError → specific import error.
• RuntimeError → generic runtime error.
• StopIteration → end of iterator.
• AssertionError → failed assert.

Arithmetic Errors:

• ArithmeticError (base)
• • ZeroDivisionError
  • OverflowError (number too large)
  • FloatingPointError

Lookup Errors:

• LookupError (base)
• • IndexError
  • KeyError

OS & System Exceptions:

• OSError → base for system errors
• • FileNotFoundError
  • PermissionError
  • TimeoutError
• EOFError → end of input reached.
• KeyboardInterrupt → Ctrl+C pressed.
• SystemExit → raised by sys.exit().

Other Useful Ones:

• MemoryError → out of memory.
• NotImplementedError → abstract method not implemented.
• IndentationError / TabError → indentation problems.
• UnicodeError (and subclasses: UnicodeEncodeError, UnicodeDecodeError, UnicodeTranslateError).

Demonstrate exception handling