异常处理 ¶

The functions described in this chapter will let you handle and raise Python exceptions. It is important to understand some of the basics of Python exception handling. It works somewhat like the Unix errno variable: there is a global indicator (per thread) of the last error that occurred. Most functions don’t clear this on success, but will set it to indicate the cause of the error on failure. Most functions also return an error indicator, usually NULL 若假设它们要返回指针，或者 -1 若它们返回整数 (例外： PyArg_*() 函数返回 1 对于成功和 0 对于故障)。

当函数因调用的某个函数失败而必须失败时，一般不设置错误指示器；它调用的函数已有设置。它负责处理错误和清零异常或在清理它保持的任何资源后返回 (譬如：对象引用或内存分配)；它应该 not 继续通常，若不准备处理错误。若由于错误而返回，重要的是向调用者指示有设置错误。若错误未被处理或被小心谨慎地传播，对 Python/C API 的额外调用可能没有如打算般的行为，且可能以神秘方式失败。

The error indicator consists of three Python objects corresponding to the Python variables sys.exc_type , sys.exc_value and sys.exc_traceback . API functions exist to interact with the error indicator in various ways. There is a separate error indicator for each thread.

void PyErr_PrintEx ( int  set_sys_last_vars ) ¶

将标准回溯打印到 sys.stderr 并清零错误指示器。仅当错误指示器有设置时才调用此函数。(否则会导致致命错误！)

若 set_sys_last_vars 非 0，变量 sys.last_type , sys.last_value and sys.last_traceback 将被分别设为打印异常的类型、值及回溯。

void PyErr_Print ( ) ¶

别名化的 PyErr_PrintEx(1) .

PyObject * PyErr_Occurred ( ) ¶

返回值：借位引用。

测试是否有设置错误指示器。若有设置，返回异常 type (首自变量到最后一次调用的一 PyErr_Set*() 函数或到 PyErr_Restore() )。若未设置，返回 NULL 。不拥有对返回值的引用，因此不需要 Py_DECREF() 它。

注意

不要将返回值与特定异常进行比较；使用 PyErr_ExceptionMatches() instead, shown below. (The comparison could easily fail since the exception may be an instance instead of a class, in the case of a class exception, or it may the a subclass of the expected exception.)

int PyErr_ExceptionMatches ( PyObject  *exc ) ¶

相当于 PyErr_GivenExceptionMatches(PyErr_Occurred(), exc) 。这才应该被调用当有实际设置异常时；会发生内存访问违反若没有引发异常。

int PyErr_GivenExceptionMatches ( PyObject  *given , PyObject  *exc ) ¶

返回 True 若 given exception matches the exception in exc 。若 exc 是类对象，这还返回 True 当 given 是子类的实例。若 exc is a tuple, all exceptions in the tuple (and recursively in subtuples) are searched for a match.

void PyErr_NormalizeException ( PyObject **exc, PyObject **val, PyObject **tb ) ¶

在某些情况下，值的返回通过 PyErr_Fetch() below can be “unnormalized”, meaning that *exc 是类对象但 *val is not an instance of the same class. This function can be used to instantiate the class in that case. If the values are already normalized, nothing happens. The delayed normalization is implemented to improve performance.

void PyErr_Clear ( ) ¶

清零错误指示器。若未设置错误指示器，则没有效果。

void PyErr_Fetch ( PyObject  **ptype , PyObject  **pvalue , PyObject  **ptraceback ) ¶

Retrieve the error indicator into three variables whose addresses are passed. If the error indicator is not set, set all three variables to NULL . If it is set, it will be cleared and you own a reference to each object retrieved. The value and traceback object may be NULL even when the type object is not.

注意

This function is normally only used by code that needs to handle exceptions or by code that needs to save and restore the error indicator temporarily.

void PyErr_Restore ( PyObject  *type , PyObject  *value , PyObject  *traceback ) ¶

Set the error indicator from the three objects. If the error indicator is already set, it is cleared first. If the objects are NULL , the error indicator is cleared. Do not pass a NULL type and non- NULL value or traceback. The exception type should be a class. Do not pass an invalid exception type or value. (Violating these rules will cause subtle problems later.) This call takes away a reference to each object: you must own a reference to each object before the call and after the call you no longer own these references. (If you don’t understand this, don’t use this function. I warned you.)

注意

This function is normally only used by code that needs to save and restore the error indicator temporarily; use PyErr_Fetch() to save the current exception state.

void PyErr_SetString ( PyObject  *type , const char  *message ) ¶

这是设置错误指示器的最常见方式。首个自变量指定异常类型；它通常是标准异常之一，如 PyExc_RuntimeError . You need not increment its reference count. The second argument is an error message; it is converted to a string object.

void PyErr_SetObject ( PyObject  *type , PyObject  *value ) ¶

此函数类似于 PyErr_SetString() 但允许您为异常值指定任意 Python 对象。

PyObject * PyErr_Format ( PyObject  *exception , const char  *format , ... ) ¶

返回值：始终 NULL。

此函数设置错误指示器并返回 NULL . exception 应该是 Python 异常类。 format 和后续参数帮助格式化错误消息；它们拥有相同的意义和值如在 PyString_FromFormat() .

void PyErr_SetNone ( PyObject  *type ) ¶

这是简写的 PyErr_SetObject(type, Py_None) .

int PyErr_BadArgument ( ) ¶

这是简写的 PyErr_SetString(PyExc_TypeError, message) ，其中 message indicates that a built-in operation was invoked with an illegal argument. It is mostly for internal use.

PyObject * PyErr_NoMemory ( ) ¶

返回值：始终 NULL。

这是简写的 PyErr_SetNone(PyExc_MemoryError) ；它返回 NULL 因此对象分配函数可以写 return PyErr_NoMemory(); 当耗尽内存时。

PyObject * PyErr_SetFromErrno ( PyObject  *type ) ¶

返回值：始终 NULL。

这是方便函数以当 C 库函数返回错误时引发异常和设置 C 变量 errno . It constructs a tuple object whose first item is the integer errno value and whose second item is the corresponding error message (gotten from strerror() ), and then calls PyErr_SetObject(type, object) . On Unix, when the errno value is EINTR , indicating an interrupted system call, this calls PyErr_CheckSignals() , and if that set the error indicator, leaves it set to that. The function always returns NULL , so a wrapper function around a system call can write return PyErr_SetFromErrno(type); when the system call returns an error.

PyObject * PyErr_SetFromErrnoWithFilenameObject ( PyObject  *type , PyObject  *filenameObject ) ¶

类似于 PyErr_SetFromErrno() , with the additional behavior that if filenameObject 不是 NULL , it is passed to the constructor of type as a third parameter. In the case of exceptions such as IOError and OSError , this is used to define the filename attribute of the exception instance.

PyObject * PyErr_SetFromErrnoWithFilename ( PyObject  *type , const char  *filename ) ¶

返回值：始终 NULL。

类似于 PyErr_SetFromErrnoWithFilenameObject() , but the filename is given as a C string.

PyObject * PyErr_SetFromWindowsErr ( int  ierr ) ¶

返回值：始终 NULL。

这是方便函数以引发 WindowsError . If called with ierr of 0 , the error code returned by a call to GetLastError() is used instead. It calls the Win32 function FormatMessage() to retrieve the Windows description of error code given by ierr or GetLastError() , then it constructs a tuple object whose first item is the ierr value and whose second item is the corresponding error message (gotten from FormatMessage() ), and then calls PyErr_SetObject(PyExc_WindowsError, object) . This function always returns NULL . Availability: Windows.

PyObject * PyErr_SetExcFromWindowsErr ( PyObject  *type , int  ierr ) ¶

返回值：始终 NULL。

类似于 PyErr_SetFromWindowsErr() , with an additional parameter specifying the exception type to be raised. Availability: Windows.

2.3 版新增。

PyObject * PyErr_SetFromWindowsErrWithFilenameObject ( int  ierr , PyObject  *filenameObject ) ¶

类似于 PyErr_SetFromWindowsErr() , with the additional behavior that if filenameObject 不是 NULL , it is passed to the constructor of WindowsError as a third parameter. Availability: Windows.

PyObject * PyErr_SetFromWindowsErrWithFilename ( int  ierr , const char  *filename ) ¶

返回值：始终 NULL。

类似于 PyErr_SetFromWindowsErrWithFilenameObject() , but the filename is given as a C string. Availability: Windows.

PyObject * PyErr_SetExcFromWindowsErrWithFilenameObject ( PyObject  *type , int  ierr , PyObject  *filename ) ¶

类似于 PyErr_SetFromWindowsErrWithFilenameObject() , with an additional parameter specifying the exception type to be raised. Availability: Windows.

2.3 版新增。

PyObject * PyErr_SetExcFromWindowsErrWithFilename ( PyObject  *type , int  ierr , const char  *filename ) ¶

返回值：始终 NULL。

类似于 PyErr_SetFromWindowsErrWithFilename() , with an additional parameter specifying the exception type to be raised. Availability: Windows.

2.3 版新增。

void PyErr_BadInternalCall ( ) ¶

这是简写的 PyErr_SetString(PyExc_SystemError, message) ，其中 message indicates that an internal operation (e.g. a Python/C API function) was invoked with an illegal argument. It is mostly for internal use.

int PyErr_WarnEx ( PyObject  *category , char  *message , int  stacklevel ) ¶

Issue a warning message. The category argument is a warning category (see below) or NULL ； message argument is a message string. stacklevel is a positive number giving a number of stack frames; the warning will be issued from the currently executing line of code in that stack frame. A stacklevel of 1 is the function calling PyErr_WarnEx() , 2 is the function above that, and so forth.

This function normally prints a warning message to sys.stderr ; however, it is also possible that the user has specified that warnings are to be turned into errors, and in that case this will raise an exception. It is also possible that the function raises an exception because of a problem with the warning machinery (the implementation imports the warnings module to do the heavy lifting). The return value is 0 if no exception is raised, or -1 if an exception is raised. (It is not possible to determine whether a warning message is actually printed, nor what the reason is for the exception; this is intentional.) If an exception is raised, the caller should do its normal exception handling (for example, Py_DECREF() owned references and return an error value).

Warning categories must be subclasses of 警告 ; the default warning category is RuntimeWarning . The standard Python warning categories are available as global variables whose names are PyExc_ followed by the Python exception name. These have the type PyObject* ; they are all class objects. Their names are PyExc_Warning , PyExc_UserWarning , PyExc_UnicodeWarning , PyExc_DeprecationWarning , PyExc_SyntaxWarning , PyExc_RuntimeWarning ，和 PyExc_FutureWarning . PyExc_Warning 是子类化的 PyExc_Exception ; the other warning categories are subclasses of PyExc_Warning .

For information about warning control, see the documentation for the warnings module and the -W option in the command line documentation. There is no C API for warning control.

int PyErr_Warn ( PyObject  *category , char  *message ) ¶

Issue a warning message. The category argument is a warning category (see below) or NULL ； message argument is a message string. The warning will appear to be issued from the function calling PyErr_Warn() , equivalent to calling PyErr_WarnEx() 采用 stacklevel of 1.

Deprecated; use PyErr_WarnEx() 代替。

int PyErr_WarnExplicit ( PyObject  *category , const char  *message , const char  *filename , int  lineno , const char  *module , PyObject  *registry ) ¶

Issue a warning message with explicit control over all warning attributes. This is a straightforward wrapper around the Python function warnings.warn_explicit() , see there for more information. The module and registry arguments may be set to NULL to get the default effect described there.

int PyErr_WarnPy3k ( char  *message , int  stacklevel ) ¶

Issue a DeprecationWarning 采用给定 message and stacklevel 若 Py_Py3kWarningFlag flag is enabled.

2.6 版新增。

int PyErr_CheckSignals ( ) ¶

This function interacts with Python’s signal handling. It checks whether a signal has been sent to the processes and if so, invokes the corresponding signal handler. If the signal module is supported, this can invoke a signal handler written in Python. In all cases, the default effect for SIGINT is to raise the KeyboardInterrupt exception. If an exception is raised the error indicator is set and the function returns -1 ；否则函数返回 0 . The error indicator may or may not be cleared if it was previously set.

void PyErr_SetInterrupt ( ) ¶

This function simulates the effect of a SIGINT signal arriving — the next time PyErr_CheckSignals() is called, KeyboardInterrupt will be raised. It may be called without holding the interpreter lock.

int PySignal_SetWakeupFd ( int  fd ) ¶

This utility function specifies a file descriptor to which a '\0' byte will be written whenever a signal is received. It returns the previous such file descriptor. The value -1 disables the feature; this is the initial state. This is equivalent to signal.set_wakeup_fd() in Python, but without any error checking. fd should be a valid file descriptor. The function should only be called from the main thread.

2.6 版新增。

PyObject * PyErr_NewException ( char  *name , PyObject  *base , PyObject  *dict ) ¶

返回值：新引用。

此实用函数创建并返回新的异常类。 name 自变量必须是新异常的名称，C 字符串形式 module.classname 。 base and dict 自变量通常为 NULL 。这创建的类对象派生自 Exception (在 C 中可访问按 PyExc_Exception ).

The __module__ attribute of the new class is set to the first part (up to the last dot) of the name argument, and the class name is set to the last part (after the last dot). The base argument can be used to specify alternate base classes; it can either be only one class or a tuple of classes. The dict argument can be used to specify a dictionary of class variables and methods.

PyObject * PyErr_NewExceptionWithDoc ( char  *name , char  *doc , PyObject  *base , PyObject  *dict ) ¶

返回值：新引用。

如同 PyErr_NewException() , except that the new exception class can easily be given a docstring: If doc 为非 NULL , it will be used as the docstring for the exception class.

2.7 版新增。

void PyErr_WriteUnraisable ( PyObject  *obj ) ¶

此实用函数将警告消息打印到 sys.stderr 当异常有设置但解释器实际引发异常不可能时。使用它，例如，当异常发生在 __del__() 方法。

调用函数采用单自变量 obj that identifies the context in which the unraisable exception occurred. The repr of obj 将被打印在警告消息中。

Unicode 异常对象 ¶

The following functions are used to create and modify Unicode exceptions from C.

PyObject * PyUnicodeDecodeError_Create ( const char  *encoding , const char  *object , Py_ssize_t  length , Py_ssize_t  start , Py_ssize_t  end , const char  *reason ) ¶

创建 UnicodeDecodeError object with the attributes encoding , object , length , start , end and reason .

PyObject * PyUnicodeEncodeError_Create ( const char  *encoding , const Py_UNICODE  *object , Py_ssize_t  length , Py_ssize_t  start , Py_ssize_t  end , const char  *reason ) ¶

创建 UnicodeEncodeError object with the attributes encoding , object , length , start , end and reason .

PyObject * PyUnicodeTranslateError_Create ( const Py_UNICODE  *object , Py_ssize_t  length , Py_ssize_t  start , Py_ssize_t  end , const char  *reason ) ¶

创建 UnicodeTranslateError object with the attributes object , length , start , end and reason .

PyObject * PyUnicodeDecodeError_GetEncoding ( PyObject  *exc ) ¶

PyObject * PyUnicodeEncodeError_GetEncoding ( PyObject  *exc ) ¶

返回 encoding 属性为给定异常对象。

PyObject * PyUnicodeDecodeError_GetObject ( PyObject  *exc ) ¶

PyObject * PyUnicodeEncodeError_GetObject ( PyObject  *exc ) ¶

PyObject * PyUnicodeTranslateError_GetObject ( PyObject  *exc ) ¶

返回 object 属性为给定异常对象。

int PyUnicodeDecodeError_GetStart ( PyObject  *exc , Py_ssize_t  *start ) ¶

int PyUnicodeEncodeError_GetStart ( PyObject  *exc , Py_ssize_t  *start ) ¶

int PyUnicodeTranslateError_GetStart ( PyObject  *exc , Py_ssize_t  *start ) ¶

获取 start attribute of the given exception object and place it into *start . start 不得为 NULL 。返回 0 当成功时， -1 当故障时。

int PyUnicodeDecodeError_SetStart ( PyObject  *exc , Py_ssize_t  start ) ¶

int PyUnicodeEncodeError_SetStart ( PyObject  *exc , Py_ssize_t  start ) ¶

int PyUnicodeTranslateError_SetStart ( PyObject  *exc , Py_ssize_t  start ) ¶

设置 start attribute of the given exception object to start 。返回 0 当成功时， -1 当故障时。

int PyUnicodeDecodeError_GetEnd ( PyObject  *exc , Py_ssize_t  *end ) ¶

int PyUnicodeEncodeError_GetEnd ( PyObject  *exc , Py_ssize_t  *end ) ¶

int PyUnicodeTranslateError_GetEnd ( PyObject  *exc , Py_ssize_t  *end ) ¶

获取 end attribute of the given exception object and place it into *end . end 不得为 NULL 。返回 0 当成功时， -1 当故障时。

int PyUnicodeDecodeError_SetEnd ( PyObject  *exc , Py_ssize_t  end ) ¶

int PyUnicodeEncodeError_SetEnd ( PyObject  *exc , Py_ssize_t  end ) ¶

int PyUnicodeTranslateError_SetEnd ( PyObject  *exc , Py_ssize_t  end ) ¶

设置 end attribute of the given exception object to end 。返回 0 当成功时， -1 当故障时。

PyObject * PyUnicodeDecodeError_GetReason ( PyObject  *exc ) ¶

PyObject * PyUnicodeEncodeError_GetReason ( PyObject  *exc ) ¶

PyObject * PyUnicodeTranslateError_GetReason ( PyObject  *exc ) ¶

返回 reason 属性为给定异常对象。

int PyUnicodeDecodeError_SetReason ( PyObject  *exc , const char  *reason ) ¶

int PyUnicodeEncodeError_SetReason ( PyObject  *exc , const char  *reason ) ¶

int PyUnicodeTranslateError_SetReason ( PyObject  *exc , const char  *reason ) ¶

设置 reason attribute of the given exception object to reason 。返回 0 当成功时， -1 当故障时。

递归控制 ¶

These two functions provide a way to perform safe recursive calls at the C level, both in the core and in extension modules. They are needed if the recursive code does not necessarily invoke Python code (which tracks its recursion depth automatically).

int Py_EnterRecursiveCall ( char  *where ) ¶

Marks a point where a recursive C-level call is about to be performed.

若 USE_STACKCHECK is defined, this function checks if the OS stack overflowed using PyOS_CheckStack() . In this is the case, it sets a MemoryError and returns a nonzero value.

The function then checks if the recursion limit is reached. If this is the case, a RuntimeError is set and a nonzero value is returned. Otherwise, zero is returned.

where should be a string such as " in instance check" to be concatenated to the RuntimeError message caused by the recursion depth limit.

void Py_LeaveRecursiveCall ( ) ¶

Ends a Py_EnterRecursiveCall() . Must be called once for each successful invocation of Py_EnterRecursiveCall() .

标准异常 ¶

All standard Python exceptions are available as global variables whose names are PyExc_ followed by the Python exception name. These have the type PyObject* ; they are all class objects. For completeness, here are all the variables:

C 名称	Python 名称	注意事项
PyExc_BaseException	BaseException	(1), (4)
PyExc_Exception	Exception	(1)
PyExc_StandardError	StandardError	(1)
PyExc_ArithmeticError	ArithmeticError	(1)
PyExc_LookupError	LookupError	(1)
PyExc_AssertionError	AssertionError
PyExc_AttributeError	AttributeError
PyExc_EOFError	EOFError
PyExc_EnvironmentError	EnvironmentError	(1)
PyExc_FloatingPointError	FloatingPointError
PyExc_IOError	IOError
PyExc_ImportError	ImportError
PyExc_IndexError	IndexError
PyExc_KeyError	KeyError
PyExc_KeyboardInterrupt	KeyboardInterrupt
PyExc_MemoryError	MemoryError
PyExc_NameError	NameError
PyExc_NotImplementedError	NotImplementedError
PyExc_OSError	OSError
PyExc_OverflowError	OverflowError
PyExc_ReferenceError	ReferenceError	(2)
PyExc_RuntimeError	RuntimeError
PyExc_SyntaxError	SyntaxError
PyExc_SystemError	SystemError
PyExc_SystemExit	SystemExit
PyExc_TypeError	TypeError
PyExc_ValueError	ValueError
PyExc_WindowsError	WindowsError	(3)
PyExc_ZeroDivisionError	ZeroDivisionError

注意事项：

1. This is a base class for other standard exceptions.

2. 这如同 weakref.ReferenceError .

3. Only defined on Windows; protect code that uses this by testing that the preprocessor macro MS_WINDOWS 有定义。

4. 2.5 版新增。

字符串异常 ¶

2.6 版改变： All exceptions to be raised or caught must be derived from BaseException . Trying to raise a string exception now raises TypeError .

内容表

• 异常处理
  • Unicode 异常对象
  • 递归控制
  • 标准异常
  • 字符串异常

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