19.4. Standard ExceptionsΒΆ
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 |
Raised when an index is not found in a sequence. |
KeyError |
Raised when the specified key is not found in the dictionary. |
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 donβt 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 doesnβt 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
| +-- 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