Python 3 Built-in Exceptions

List of built-in exceptions in Python 3.

Base Classes

These exceptions are generally used as base classes for other exceptions.

Exception	Description
`BaseException`	The base class for all built-in exceptions. It is not meant to be directly inherited by user-defined classes (for that, use `Exception` below).
`Exception`	All built-in, non-system-exiting exceptions are derived from this class. All user-defined exceptions should also be derived from this class.
`ArithmeticError`	The base class for built-in exceptions that are raised for various arithmetic errors. These are: `OverflowError`, `ZeroDivisionError`, `FloatingPointError`.
`BufferError`	Raised when a buffer related operation cannot be performed.
`LookupError`	The base class for exceptions that are raised when a key or index used on a mapping or sequence is invalid. These are: `IndexError` and `KeyError`.

Concrete Exceptions

These are the exceptions that are usually raised.

Exception	Description
`AssertionError`	Raised when an `assert` statement fails.
`AttributeError`	Raised when an attribute reference or assignment fails. When an object does not support attribute references or attribute assignments at all, `TypeError` is raised.
`EOFError`	Raised when the `input()` function hits an end-of-file condition (EOF) without reading any data.
`FloatingPointError`	Raised when a floating point operation fails.
`GeneratorExit`	Raised when a generator or coroutine is closed. Technically, this is not an error, and the `GeneratorExit` exception directly inherits from `BaseException` instead of `Exception`.
`ImportError`	Raised when the `import` statement fails when trying to load a module. This exception is also raised when the `from` in `from ... import` has a name that cannot be found.
`ModuleNotFoundError`	A subclass of `ImportError` which is raised by import when a module could not be located. This exception is also raised when `None` is found in `sys.modules`.
`IndexError`	Raised when a sequence subscript is out of range.
`KeyError`	Raised when a mapping (dictionary) key is not found in the set of existing keys.
`KeyboardInterrupt`	Raised when the user hits the interrupt key (typically `Control-C` or `Delete`).
`MemoryError`	Raised when an operation runs out of memory but the situation may still be rescued (by deleting some objects).
`NameError`	Raised when a local or global name is not found. This applies only to unqualified names.
`NotImplementedError`	This exception is derived from `RuntimeError`. In user defined base classes, abstract methods should raise this exception when they require derived classes to override the method, or while the class is being developed to indicate that the real implementation still needs to be added.
`OSError()`	This exception is raised when a system function returns a system-related error, including I/O failures such as "file not found" or "disk full".
`OverflowError`	Raised when the result of an arithmetic operation is too large to be represented.
`RecursionError`	This exception is derived from `RuntimeError`. It is raised when the interpreter detects that the maximum recursion depth is exceeded.
`ReferenceError`	Raised when a weak reference proxy, created by the `weakref.proxy()` function, is used to access an attribute of the referent after it has been garbage collected.
`RuntimeError`	Raised when an error is detected that doesnâ€™t fall in any of the other categories.
`StopIteration`	Raised by the `next()` function and an iterator's `__next__()` method to signal that there are no further items produced by the iterator.
`StopAsyncIteration`	Must be raised by `__anext__()` method of an asynchronous iterator object to stop the iteration.
`SyntaxError`	Raised when the parser encounters a syntax error.
`IndentationError`	Base class for syntax errors related to incorrect indentation. This is a subclass of `SyntaxError`.
`TabError`	Raised when indentation contains an inconsistent use of tabs and spaces. This is a subclass of `IndentationError`.
`SystemError`	Raised when the interpreter finds an internal error, but it's not serious enough to exit the interpreter.
`SystemExit`	This exception is raised by the `sys.exit()` function, and (when it is not handled) causes the Python interpreter to exit.
`TypeError`	Raised when an operation or function is applied to an object of inappropriate type.
`UnboundLocalError`	Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable. This is a subclass of `NameError`.
`UnicodeError`	Raised when a Unicode-related encoding or decoding error occurs. It is a subclass of `ValueError`.
`UnicodeEncodeError`	Raised when a Unicode-related error occurs during encoding. It is a subclass of `UnicodeError`.
`UnicodeDecodeError`	Raised when a Unicode-related error occurs during encoding. It is a subclass of `UnicodeError`.
`UnicodeTranslateError`	Raised when a Unicode-related error occurs during encoding. It is a subclass of `UnicodeError`.
`ValueError`	Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception.
`ZeroDivisionError`	Raised when the second argument of a division or modulo operation is zero.

OS Exceptions

These exceptions are subclasses of OSError. They get raised depending on the actual system error code.

Exception	Description
`BlockingIOError`	Raised when an operation would block on an object (e.g. socket) set for non-blocking operation.
`ChildProcessError`	Raised when an operation on a child process failed.
`ConnectionError`	A base class for connection-related issues.
`BrokenPipeError`	A subclass of `ConnectionError`, raised when trying to write on a pipe while the other end has been closed, or trying to write on a socket which has been shutdown for writing.
`ConnectionAbortedError`	A subclass of `ConnectionError`, raised when a connection attempt is aborted by the peer.
`ConnectionRefusedError`	A subclass of `ConnectionError`, raised when a connection is reset by the peer.
`FileExistsError`	Raised when trying to create a file or directory which already exists.
`FileNotFoundError`	Raised when a file or directory is requested but doesnâ€™t exist.
`InterruptedError`	Raised when a system call is interrupted by an incoming signal.
`IsADirectoryError`	Raised when a file operation is requested on a directory.
`NotADirectoryError`	Raised when a directory operation is requested on something which is not a directory.
`PermissionError`	Raised when trying to run an operation without the adequate access rights.
`ProcessLookupError`	Raised when a given process doesnâ€™t exist.
`TimeoutError`	Raised when a system function timed out at the system level.

Warnings

The following exceptions are used as warning categories.

Exception	Description
`Warning`	Base class for warning categories.
`UserWarning`	Base class for warnings generated by user code.
`DeprecationWarning`	Base class for warnings about deprecated features.
`PendingDeprecationWarning`	Base class for warnings about features which will be deprecated in the future.
`SyntaxWarning`	Base class for warnings about dubious syntax.
`RuntimeWarning`	Base class for warnings about dubious runtime behavior.
`FutureWarning`	Base class for warnings about constructs that will change semantically in the future.
`ImportWarning`	Base class for warnings about probable mistakes in module imports.
`UnicodeWarning`	Base class for warnings related to Unicode.
`BytesWarning`	Base class for warnings related to `bytes` and `bytearray`.
`ResourceWarning`	Base class for warnings related to resource usage.