Lesson 9: No Object is an Island > Built-in Exceptions | Python Programming | Department of Computing

Lesson 9

No Object is an Island

Chapter 9: Exception handling

Built-in Exceptions

face Josiah Wang

Below is the list of all Python built-in exceptions (reproduced from the official documentation).

All built-in exceptions are special instances of BaseException, and is arranged in a class hierarchy. So Exception is a special kind of BaseException, ZeroDivisionError is a special kind of ArithmeticError, etc. We will discuss more about class hierarchy in the next lesson.

You may have already encountered some of these exceptions. How many of these classes do you recognise?

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StopAsyncIteration
      +-- ArithmeticError
      |    +-- FloatingPointError
      |    +-- OverflowError
      |    +-- ZeroDivisionError
      +-- AssertionError
      +-- AttributeError
      +-- BufferError
      +-- EOFError
      +-- ImportError
      |    +-- ModuleNotFoundError
      +-- LookupError
      |    +-- IndexError
      |    +-- KeyError
      +-- MemoryError
      +-- NameError
      |    +-- UnboundLocalError
      +-- OSError
      |    +-- BlockingIOError
      |    +-- ChildProcessError
      |    +-- ConnectionError
      |    |    +-- BrokenPipeError
      |    |    +-- ConnectionAbortedError
      |    |    +-- ConnectionRefusedError
      |    |    +-- ConnectionResetError
      |    +-- FileExistsError
      |    +-- FileNotFoundError
      |    +-- InterruptedError
      |    +-- IsADirectoryError
      |    +-- NotADirectoryError
      |    +-- PermissionError
      |    +-- ProcessLookupError
      |    +-- TimeoutError
      +-- ReferenceError
      +-- RuntimeError
      |    +-- NotImplementedError
      |    +-- RecursionError
      +-- SyntaxError
      |    +-- IndentationError
      |         +-- TabError
      +-- SystemError
      +-- TypeError
      +-- ValueError
      |    +-- UnicodeError
      |         +-- UnicodeDecodeError
      |         +-- UnicodeEncodeError
      |         +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
           +-- ImportWarning
           +-- UnicodeWarning
           +-- BytesWarning
           +-- ResourceWarning

Try skimming through the documentation for more details about these Exceptions. Some Exceptions that you might encounter often include ModuleNotFoundError, TypeError, ValueError, IndexError (e.g. trying to access a list element that is beyond the size of the list), KeyError (e.g. accessing a dictionary element with an invalid key), FileNotFoundError, and one of the ArithmeticErrors. Understanding what these exceptions represent will enable you to debug your code better in the future.

You are also encouraged to choose a semantically suitable Exception if you are raising your own exceptions.