6. 内置异常 ¶

Exceptions should be class objects. The exceptions are defined in the module exceptions . This module never needs to be imported explicitly: the exceptions are provided in the built-in namespace as well as the exceptions 模块。

For class exceptions, in a try 语句采用 except clause that mentions a particular class, that clause also handles any exception classes derived from that class (but not exception classes from which it is derived). Two exception classes that are not related via subclassing are never equivalent, even if they have the same name.

The built-in exceptions listed below can be generated by the interpreter or built-in functions. Except where mentioned, they have an “associated value” indicating the detailed cause of the error. This may be a string or a tuple containing several items of information (e.g., an error code and a string explaining the code). The associated value is the second argument to the raise statement. If the exception class is derived from the standard root class BaseException , the associated value is present as the exception instance’s args 属性。

User code can raise built-in exceptions. This can be used to test an exception handler or to report an error condition “just like” the situation in which the interpreter raises the same exception; but beware that there is nothing to prevent user code from raising an inappropriate error.

The built-in exception classes can be subclassed to define new exceptions; programmers are encouraged to derive new exceptions from the Exception class or one of its subclasses, and not from BaseException . More information on defining exceptions is available in the Python Tutorial under 用户定义异常 .

The following exceptions are only used as base classes for other exceptions.

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() or unicode() 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.

2.5 版新增。

args ¶

The tuple of arguments given to the exception constructor. Some built-in exceptions (like IOError ) 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.

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。

Changed in version 2.5: Changed to inherit from BaseException .

exception StandardError ¶

The base class for all built-in exceptions except StopIteration , GeneratorExit , KeyboardInterrupt and SystemExit . StandardError itself is derived from Exception .

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() .

exception EnvironmentError ¶

The base class for exceptions that can occur outside the Python system: IOError , OSError . When exceptions of this type are created with a 2-tuple, the first item is available on the instance’s errno attribute (it is assumed to be an error number), and the second item is available on the strerror attribute (it is usually the associated error message). The tuple itself is also available on the args 属性。

1.5.2 版新增。

当 EnvironmentError exception is instantiated with a 3-tuple, the first two items are available as above, while the third item is available on the filename attribute. However, for backwards compatibility, the args 属性是包含仅前 2 构造函数自变量的 2 元素元组。

The filename 属性为 None when this exception is created with other than 3 arguments. The errno and strerror attributes are also None when the instance was created with other than 2 or 3 arguments. In this last case, args contains the verbatim constructor arguments as a tuple.

The following exceptions are the exceptions that are actually raised.

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 ) 或赋值失败。(当对象根本不支持属性引用或属性赋值时， TypeError 被引发)。

exception EOFError ¶

Raised when one of the built-in functions ( input() or raw_input() ) hits an end-of-file condition (EOF) without reading any data. (N.B.: the file.read() and file.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 ’s close() method is called. It directly inherits from BaseException 而不是 StandardError 由于它在技术上不是错误。

2.5 版新增。

2.6 版改变： Changed to inherit from BaseException .

exception IOError ¶

Raised when an I/O operation (such as a print statement, the built-in open() function or a method of a file object) fails for an I/O-related reason, e.g., “file not found” or “disk full”.

This class is derived from EnvironmentError . See the discussion above for more information on exception instance attributes.

2.6 版改变： Changed socket.error to use this as a base class.

exception ImportError ¶

被引发当 import statement fails to find the module definition or when a from ... import fails to find a name that is to be imported.

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 a plain integer, TypeError 被引发)。

exception KeyError ¶

被引发当在现有键集中找不到映射 (字典) 键时。

exception KeyboardInterrupt ¶

被引发当用户命中中断键时 (通常 Control-C or 删除 ). During execution, a check for interrupts is made regularly. Interrupts typed when a built-in function input() or raw_input() is waiting for input also raise this exception. The exception inherits from BaseException 以免被意外捕获通过代码捕获 Exception 从而防止解释器退出。

Changed in version 2.5: Changed to inherit from BaseException .

exception MemoryError ¶

被引发当操作耗尽内存但情况仍可以挽救 (通过删除一些对象)。关联值是指示哪种 (内部) 操作耗尽内存的字符串。注意，由于底层内存管理体系结构（C 的 malloc() 函数)，解释器可能并不会总是能够从这种情况完全恢复；尽管如此，它会引发异常，以便在程序失控的情况下打印堆栈回溯。

exception NameError ¶

被引发当找不到局部 (或全局) 名称时。这仅适用于不合格名称。关联值是包括找不到名称的错误消息。

exception NotImplementedError ¶

此异常派生自 RuntimeError . In user defined base classes, abstract methods should raise this exception when they require derived classes to override the method.

1.5.2 版新增。

exception OSError ¶

此异常派生自 EnvironmentError . It is raised when a function returns a system-related error (not for illegal argument types or other incidental errors). The errno attribute is a numeric error code from errno ，和 strerror attribute is the corresponding string, as would be printed by the C function perror() . See the module errno , which contains names for the error codes defined by the underlying operating system.

对于涉及文件系统路径的异常 (譬如 chdir() or unlink() ), the exception instance will contain a third attribute, filename , which is the file name passed to the function.

1.5.2 版新增。

exception OverflowError ¶

Raised when the result of an arithmetic operation is too large to be represented. This cannot occur for long integers (which would rather raise MemoryError than give up) and for most operations with plain integers, which return a long integer instead. Because of the lack of standardization of floating point exception handling in C, most floating point operations also aren’t checked.

exception ReferenceError ¶

此异常被引发当弱引用代理时，创建通过 weakref.proxy() 函数，用于访问所指属性在它被垃圾收集之后。有关弱引用的更多信息，见 weakref 模块。

New in version 2.2: Previously known as the weakref.ReferenceError 异常。

exception RuntimeError ¶

被引发当检测到不属于任何其它类别的错误时。关联值是指示哪里准确出错的字符串。

exception StopIteration ¶

Raised by an iterator ’s next() method to signal that there are no further values. This is derived from Exception 而不是 StandardError , since this is not considered an error in its normal application.

2.2 版新增。

exception SyntaxError ¶

被引发当剖析器遇到句法错误时。这可能发生在 import statement, in an exec statement, in a call to the built-in function eval() or input() ，或当读取初始脚本或标准输入 (也交互) 时。

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 ¶

不正确缩进相关句法错误的基类。这是子类化的 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() function. When it is not handled, the Python interpreter exits; no stack traceback is printed. If the associated value is a plain 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.

Instances have an attribute code which is set to the proposed exit status or error message (defaulting to None ). Also, this exception derives directly from BaseException 和不 StandardError , since it is not technically an error.

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() ).

The exception inherits from BaseException 而不是 StandardError or 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.

Changed in version 2.5: Changed to inherit from BaseException .

exception TypeError ¶

被引发当操作 (或函数) 被应用于不适当类型的对象时。关联值是字符串，给出类型不匹配的有关细节。

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 .

2.0 版新增。

exception UnicodeError ¶

被引发当发生 Unicode 相关编码或解码错误时。它是子类化的 ValueError .

UnicodeError 拥有描述编码 (或解码) 错误的属性。例如， 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 ¶

试图编码 (或解码) 的编解码器对象。

start ¶

无效数据的第一索引在 object .

end ¶

最后无效数据之后的索引在 object .

2.0 版新增。

exception UnicodeEncodeError ¶

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

2.3 版新增。

exception UnicodeDecodeError ¶

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

2.3 版新增。

exception UnicodeTranslateError ¶

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

2.3 版新增。

exception ValueError ¶

被引发当操作 (或函数) 收到类型正确但值不合适的自变量，且未按更准确异常描述这种情况，譬如 IndexError .

exception VMSError ¶

Only available on VMS. Raised when a VMS-specific error occurs.

exception WindowsError ¶

Raised when a Windows-specific error occurs or when the error number does not correspond to an errno value. The winerror and strerror values are created from the return values of the GetLastError() and FormatMessage() functions from the Windows Platform API. The errno value maps the winerror value to corresponding errno.h values. This is a subclass of OSError .

2.0 版新增。

Changed in version 2.5: Previous versions put the GetLastError() codes into errno .

exception ZeroDivisionError ¶

被引发当除法 (或模) 运算的第 2 自变量为 0。关联值是指示操作数和运算类型的字符串。

下列异常被用作警告类别；见 warnings module for more information.

exception 警告 ¶

警告类别的基类。

exception UserWarning ¶

由用户代码生成的警告的基类。

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.

2.5 版新增。

exception UnicodeWarning ¶

Base class for warnings related to Unicode.

2.5 版新增。

exception BytesWarning ¶

Base class for warnings related to bytes and bytearray.

2.6 版新增。

BaseException
 +-- SystemExit
 +-- KeyboardInterrupt
 +-- GeneratorExit
 +-- Exception
      +-- StopIteration
      +-- StandardError
      |    +-- BufferError
      |    +-- ArithmeticError
      |    |    +-- FloatingPointError
      |    |    +-- OverflowError
      |    |    +-- ZeroDivisionError
      |    +-- AssertionError
      |    +-- AttributeError
      |    +-- EnvironmentError
      |    |    +-- IOError
      |    |    +-- OSError
      |    |         +-- WindowsError (Windows)
      |    |         +-- VMSError (VMS)
      |    +-- EOFError
      |    +-- ImportError
      |    +-- LookupError
      |    |    +-- IndexError
      |    |    +-- KeyError
      |    +-- MemoryError
      |    +-- NameError
      |    |    +-- UnboundLocalError
      |    +-- ReferenceError
      |    +-- RuntimeError
      |    |    +-- NotImplementedError
      |    +-- SyntaxError
      |    |    +-- IndentationError
      |    |         +-- TabError
      |    +-- SystemError
      |    +-- TypeError
      |    +-- ValueError
      |         +-- UnicodeError
      |              +-- UnicodeDecodeError
      |              +-- UnicodeEncodeError
      |              +-- UnicodeTranslateError
      +-- Warning
           +-- DeprecationWarning
           +-- PendingDeprecationWarning
           +-- RuntimeWarning
           +-- SyntaxWarning
           +-- UserWarning
           +-- FutureWarning
	   +-- ImportWarning
	   +-- UnicodeWarning
	   +-- BytesWarning