# 19.4. Standard Exceptions¶

Most of the standard exceptions built into Python are listed below. They are organized into related groups based on the types of issues they deal with.

Language Exceptions

Description

StandardError

Base class for all built-in exceptions except StopIteration and SystemExit.

ImportError

Raised when an import statement fails.

SyntaxError

Raised when there is an error in Python syntax.

IndentationError

Raised when indentation is not specified properly.

NameError

Raised when an identifier is not found in the local or global namespace.

UnboundLocalError

Raised when trying to access a local variable in a function or method but no value has been assigned to it.

TypeError

Raised when an operation or function is attempted that is invalid for the specified data type.

LookupError

Base class for all lookup errors.

IndexError

KeyError

ValueError

Raised when the built-in function for a data type has the valid type of arguments, but the arguments have invalid values specified.

RuntimeError

Raised when a generated error does not fall into any category.

MemoryError

Raised when a operation runs out of memory.

RecursionError

Raised when the maximum recursion depth has been exceeded.

SystemError

Raised when the interpreter finds an internal problem, but when this error is encountered the Python interpreter does not exit.

Math Exceptions

Description

ArithmeticError

Base class for all errors that occur for numeric calculation. You know a math error occurred, but you don’t know the specific error.

OverflowError

Raised when a calculation exceeds maximum limit for a numeric type.

FloatingPointError

Raised when a floating point calculation fails.

ZeroDivisonError

Raised when division or modulo by zero takes place for all numeric types.

I/O Exceptions

Description

FileNotFoundError

Raised when a file or directory is requested but doesn’t exist.

IOError

Raised when an input/ output operation fails, such as the print statement or the open() function when trying to open a file that does not exist. Also raised for operating system-related errors.

PermissionError

Raised when trying to run an operation without the adequate access rights.

EOFError

Raised when there is no input from either the raw_input() or input() function and the end of file is reached.

KeyboardInterrupt

Raised when the user interrupts program execution, usually by pressing Ctrl+c.

Other Exceptions

Description

Exception

Base class for all exceptions. This catches most exception messages.

StopIteration

Raised when the next() method of an iterator does not point to any object.

AssertionError

Raised in case of failure of the Assert statement.

SystemExit

Raised when Python interpreter is quit by using the sys.exit() function. If not handled in the code, it causes the interpreter to exit.

OSError

Raises for operating system related errors.

EnvironmentError

Base class for all exceptions that occur outside the Python environment.

AttributeError

Raised in case of failure of an attribute reference or assignment.

NotImplementedError

Raised when an abstract method that needs to be implemented in an inherited class is not actually implemented.

All exceptions are objects. The classes that define the objects are organized in a hierarchy, which is shown below. This is important because the parent class of a set of related exceptions will catch all exception messages for itself and its child exceptions. For example, an ArithmeticError exception will catch itself and all FloatingPointError, OverflowError, and ZeroDivisionError exceptions.

BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StopAsyncIteration
+-- ArithmeticError
|    +-- FloatingPointError
|    +-- OverflowError
|    +-- ZeroDivisionError
+-- AssertionError
+-- AttributeError
+-- BufferError
+-- EOFError
+-- ImportError
+-- LookupError
|    +-- IndexError
|    +-- KeyError
+-- MemoryError
+-- NameError
|    +-- UnboundLocalError
+-- OSError
|    +-- BlockingIOError
|    +-- ChildProcessError
|    +-- ConnectionError
|    |    +-- BrokenPipeError
|    |    +-- ConnectionAbortedError
|    |    +-- ConnectionRefusedError
|    |    +-- ConnectionResetError
|    +-- FileExistsError
|    +-- FileNotFoundError
|    +-- InterruptedError
|    +-- 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