5. 内置异常 ¶

5.1. 基类 ¶

以下异常主要用作其它异常的基类。

exception 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 )。若 str() is called on an instance of this class, the representation of the argument(s) to the instance are returned, or the empty string when there were no arguments.

args ¶

The tuple of arguments given to the exception constructor. Some built-in exceptions (like OSError ) expect a certain number of arguments and assign a special meaning to the elements of this tuple, while others are usually called only with a single string giving an error message.

with_traceback ( tb ) ¶

此方法设置 tb as the new traceback for the exception and returns the exception object. It is usually used in exception handling code like this:

try:
    ...
except SomeException:
    tb = sys.exc_info()[2]
    raise OtherException(...).with_traceback(tb)
												

exception Exception ¶

所有内置、非系统退出异常都派生自此类。所有用户定义异常也应派生自此类。

exception ArithmeticError ¶

The base class for those built-in exceptions that are raised for various arithmetic errors: OverflowError , ZeroDivisionError , FloatingPointError .

exception BufferError ¶

被引发当 buffer 相关操作无法履行。

exception LookupError ¶

The base class for the exceptions that are raised when a key or index used on a mapping or sequence is invalid: IndexError , KeyError . This can be raised directly by codecs.lookup() .

5.2. 具体异常 ¶

以下异常是通常引发的异常。

exception AssertionError ¶

被引发当 assert 语句失败。

exception AttributeError ¶

被引发当属性引用 (见 属性引用 ) or assignment fails. (When an object does not support attribute references or attribute assignments at all, TypeError is raised.)

exception EOFError ¶

Raised when the input() function hits an end-of-file condition (EOF) without reading any data. (N.B.: the io.IOBase.read() and io.IOBase.readline() methods return an empty string when they hit EOF.)

exception FloatingPointError ¶

Raised when a floating point operation fails. This exception is always defined, but can only be raised when Python is configured with the --with-fpectl option, or the WANT_SIGFPE_HANDLER symbol is defined in the pyconfig.h 文件。

exception GeneratorExit ¶

被引发当 generator or 协程 is closed; see generator.close() and coroutine.close() . It directly inherits from BaseException 而不是 Exception since it is technically not an error.

exception ImportError ¶

Raised when the import statement has troubles trying to load a module. Also raised when the “from list” in from ... import has a name that cannot be found.

name and path attributes can be set using keyword-only arguments to the constructor. When set they represent the name of the module that was attempted to be imported and the path to any file which triggered the exception, respectively.

3.3 版改变： 添加 name and path 属性。

exception ModuleNotFoundError ¶

子类化的 ImportError which is raised by import when a module could not be located. It is also raised when None is found in sys.modules .

3.6 版新增。

exception IndexError ¶

Raised when a sequence subscript is out of range. (Slice indices are silently truncated to fall in the allowed range; if an index is not an integer, TypeError is raised.)

exception KeyError ¶

Raised when a mapping (dictionary) key is not found in the set of existing keys.

exception KeyboardInterrupt ¶

Raised when the user hits the interrupt key (normally Control-C or Delete ). During execution, a check for interrupts is made regularly. The exception inherits from BaseException so as to not be accidentally caught by code that catches Exception and thus prevent the interpreter from exiting.

exception MemoryError ¶

Raised when an operation runs out of memory but the situation may still be rescued (by deleting some objects). The associated value is a string indicating what kind of (internal) operation ran out of memory. Note that because of the underlying memory management architecture (C’s malloc() function), the interpreter may not always be able to completely recover from this situation; it nevertheless raises an exception so that a stack traceback can be printed, in case a run-away program was the cause.

exception NameError ¶

Raised when a local or global name is not found. This applies only to unqualified names. The associated value is an error message that includes the name that could not be found.

exception 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.

注意

It should not be used to indicate that an operator or method is not meant to be supported at all – in that case either leave the operator / method undefined or, if a subclass, set it to None .

注意

NotImplementedError and NotImplemented are not interchangeable, even though they have similar names and purposes. See NotImplemented for details on when to use it.

exception OSError ( [ arg ] ) ¶

exception OSError ( errno , strerror [ , filename [ , winerror [ , filename2 ] ] ] )

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” (not for illegal argument types or other incidental errors).

The second form of the constructor sets the corresponding attributes, described below. The attributes default to None if not specified. For backwards compatibility, if three arguments are passed, the args attribute contains only a 2-tuple of the first two constructor arguments.

The constructor often actually returns a subclass of OSError , as described in OS exceptions below. The particular subclass depends on the final errno value. This behaviour only occurs when constructing OSError directly or via an alias, and is not inherited when subclassing.

errno ¶

A numeric error code from the C variable errno .

winerror ¶

Under Windows, this gives you the native Windows error code. The errno attribute is then an approximate translation, in POSIX terms, of that native error code.

Under Windows, if the winerror constructor argument is an integer, the errno attribute is determined from the Windows error code, and the errno argument is ignored. On other platforms, the winerror argument is ignored, and the winerror attribute does not exist.

strerror ¶

The corresponding error message, as provided by the operating system. It is formatted by the C functions perror() under POSIX, and FormatMessage() under Windows.

filename ¶

filename2 ¶

For exceptions that involve a file system path (such as open() or os.unlink() ), filename is the file name passed to the function. For functions that involve two file system paths (such as os.rename() ), filename2 corresponds to the second file name passed to the function.

3.3 版改变： EnvironmentError , IOError , WindowsError , socket.error , select.error and mmap.error have been merged into OSError , and the constructor may return a subclass.

3.4 版改变： filename attribute is now the original file name passed to the function, instead of the name encoded to or decoded from the filesystem encoding. Also, the filename2 constructor argument and attribute was added.

exception OverflowError ¶

Raised when the result of an arithmetic operation is too large to be represented. This cannot occur for integers (which would rather raise MemoryError than give up). However, for historical reasons, OverflowError is sometimes raised for integers that are outside a required range. Because of the lack of standardization of floating point exception handling in C, most floating point operations are not checked.

exception RecursionError ¶

This exception is derived from RuntimeError . It is raised when the interpreter detects that the maximum recursion depth (see sys.getrecursionlimit() ) is exceeded.

3.5 版新增： Previously, a plain RuntimeError 被引发。

exception ReferenceError ¶

This exception is 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. For more information on weak references, see the weakref 模块。

exception RuntimeError ¶

Raised when an error is detected that doesn’t fall in any of the other categories. The associated value is a string indicating what precisely went wrong.

exception StopIteration ¶

Raised by built-in function next() 和 iterator ’s __next__() method to signal that there are no further items produced by the iterator.

The exception object has a single attribute value , which is given as an argument when constructing the exception, and defaults to None .

当 generator or 协程 function returns, a new StopIteration instance is raised, and the value returned by the function is used as the value parameter to the constructor of the exception.

If a generator function defined in the presence of a from __future__ import generator_stop directive raises StopIteration , it will be converted into a RuntimeError (retaining the StopIteration as the new exception’s cause).

3.3 版改变： 添加 value attribute and the ability for generator functions to use it to return a value.

3.5 版改变： Introduced the RuntimeError transformation.

exception StopAsyncIteration ¶

Must be raised by __anext__() method of an 异步迭代器 object to stop the iteration.

3.5 版新增。

exception SyntaxError ¶

Raised when the parser encounters a syntax error. This may occur in an import statement, in a call to the built-in functions exec() or eval() , or when reading the initial script or standard input (also interactively).

Instances of this class have attributes filename , lineno , offset and text for easier access to the details. str() of the exception instance returns only the message.

exception IndentationError ¶

Base class for syntax errors related to incorrect indentation. This is a subclass of SyntaxError .

exception TabError ¶

Raised when indentation contains an inconsistent use of tabs and spaces. This is a subclass of IndentationError .

exception SystemError ¶

Raised when the interpreter finds an internal error, but the situation does not look so serious to cause it to abandon all hope. The associated value is a string indicating what went wrong (in low-level terms).

You should report this to the author or maintainer of your Python interpreter. Be sure to report the version of the Python interpreter ( sys.version ; it is also printed at the start of an interactive Python session), the exact error message (the exception’s associated value) and if possible the source of the program that triggered the error.

exception SystemExit ¶

此异常被引发通过 sys.exit() 函数。它继承自 BaseException 而不是 Exception so that it is not accidentally caught by code that catches Exception . This allows the exception to properly propagate up and cause the interpreter to exit. When it is not handled, the Python interpreter exits; no stack traceback is printed. The constructor accepts the same optional argument passed to sys.exit() . If the value is an integer, it specifies the system exit status (passed to C’s exit() function); if it is None , the exit status is zero; if it has another type (such as a string), the object’s value is printed and the exit status is one.

调用 sys.exit() is translated into an exception so that clean-up handlers ( finally clauses of try statements) can be executed, and so that a debugger can execute a script without running the risk of losing control. The os._exit() function can be used if it is absolutely positively necessary to exit immediately (for example, in the child process after a call to os.fork() ).

code ¶

传递给构造函数的退出状态或错误消息。(默认为 None .)

exception TypeError ¶

Raised when an operation or function is applied to an object of inappropriate type. The associated value is a string giving details about the type mismatch.

This exception may be raised by user code to indicate that an attempted operation on an object is not supported, and is not meant to be. If an object is meant to support a given operation but has not yet provided an implementation, NotImplementedError is the proper exception to raise.

Passing arguments of the wrong type (e.g. passing a list when an int is expected) should result in a TypeError , but passing arguments with the wrong value (e.g. a number outside expected boundaries) should result in a ValueError .

exception 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 .

exception UnicodeError ¶

Raised when a Unicode-related encoding or decoding error occurs. It is a subclass of ValueError .

UnicodeError has attributes that describe the encoding or decoding error. For example, err.object[err.start:err.end] gives the particular invalid input that the codec failed on.

encoding ¶

引发错误的编码名称。

reason ¶

描述特定编解码器错误的字符串。

object ¶

The object the codec was attempting to encode or decode.

start ¶

The first index of invalid data in object .

end ¶

The index after the last invalid data in object .

exception UnicodeEncodeError ¶

Raised when a Unicode-related error occurs during encoding. It is a subclass of UnicodeError .

exception UnicodeDecodeError ¶

Raised when a Unicode-related error occurs during decoding. It is a subclass of UnicodeError .

exception UnicodeTranslateError ¶

Raised when a Unicode-related error occurs during translating. It is a subclass of UnicodeError .

exception ValueError ¶

Raised when an 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 such as IndexError .

exception ZeroDivisionError ¶

Raised when the second argument of a division or modulo operation is zero. The associated value is a string indicating the type of the operands and the operation.

The following exceptions are kept for compatibility with previous versions; starting from Python 3.3, they are aliases of OSError .

exception EnvironmentError ¶

exception IOError ¶

exception WindowsError ¶

只可用于 Windows。

5.3. 警告 ¶

The following exceptions are used as warning categories; see the warnings module for more information.

exception 警告 ¶

Base class for warning categories.

exception UserWarning ¶

Base class for warnings generated by user code.

exception DeprecationWarning ¶

Base class for warnings about deprecated features.

exception PendingDeprecationWarning ¶

Base class for warnings about features which will be deprecated in the future.

exception SyntaxWarning ¶

Base class for warnings about dubious syntax.

exception RuntimeWarning ¶

Base class for warnings about dubious runtime behavior.

exception FutureWarning ¶

Base class for warnings about constructs that will change semantically in the future.

exception ImportWarning ¶

Base class for warnings about probable mistakes in module imports.

exception UnicodeWarning ¶

Base class for warnings related to Unicode.

exception BytesWarning ¶

Base class for warnings related to bytes and bytearray .

exception ResourceWarning ¶

Base class for warnings related to resource usage.

3.2 版新增。

5.4. 异常层次结构 ¶

The class hierarchy for built-in exceptions is:

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