# 例外處理

本章描述的函数将让你处理和触发 Python 异常。了解一些 Python 异常处理的基本知识是很重要的。 它的工作原理有点像 POSIX 的 `errno` 变量：（每个线程）有一个全局指示器显示最近发生的错误。 大多数 C API 函数不会在成功时理会它，但会在失败时设置它来指示错误的原因。 多数 C API 函数也返回一个错误指示器，如果它们应该返回一个指针，通常返回 `NULL`，如果返回一个整数，则返回 `-1` (例外: `PyArg_*()` 函数成功时返回 `1` 而失败时返回 `0`)。

具体地说，错误指示器由三个对象指针组成：异常的类型，异常的值，和回溯对象。如果没有错误被设置，这些指针都可以是 `NULL` （尽管一些组合使禁止的，例如，如果异常类型是 `NULL` ，你不能有一个非 `NULL` 的回溯）。

当一个函数由于它调用的某个函数失败而必须失败时，通常不会设置错误指示器；它调用的那个函数已经设置了它。而它负责处理错误和清理异常，或在清除其拥有的所有资源后返回（如对象应用或内存分配）。如果不准备处理异常，则 不 应该正常地继续。如果是由于一个错误返回，那么一定要向调用者表明已经设置了错误。如果错误没有得到处理或小心传播，对 Python/C API的其它调用可能不会有预期的行为，并且可能会以某种神秘的方式失败。

備註

错误指示器 不是 `sys.exc_info()` 的执行结果。前者对应尚未捕获的异常（异常还在传播），而后者在捕获异常后返回这个异常（异常已经停止传播）。

## 打印和清理

void `PyErr_Clear`()

  清除错误指示器。如果没有设置错误指示器，则不会有作用。

void `PyErr_PrintEx`(int set_sys_last_vars)

  将标准回溯打印到 `sys.stderr` 并清除错误指示器。除非 错误是 `SystemExit`，这种情况下不会打印回溯进程，且会退出 Python 进程，并显示 `SystemExit` 实例指定的错误代码。

  只有在错误指示器被设置时才需要调用这个函数，否则这会导致错误！

  如果 set_sys_last_vars 非零，则变量 `sys.last_type`，`sys.last_value` 和 `sys.last_traceback` 将分别设置为打印异常的类型，值和回溯。

void `PyErr_Print`()

  `PyErr_PrintEx(1)` 的别名。

void `PyErr_WriteUnraisable`(PyObject *obj)

  使用当前异常和 obj 参数调用 `sys.unraisablehook()`。

  当设置了异常，但解释器不可能实际地触发异常时，这个实用函数向 `sys.stderr` 打印一个警告信息。例如，当 `__del__()` 方法中发生异常时使用这个函数。

  该函数使用单个参数 obj 进行调用，该参数标识发生不可触发异常的上下文。如果可能，obj 的报告将打印在警告消息中。

  调用此函数时必须设置一个异常。

## 抛出异常

这些函数可帮助你设置当前线程的错误指示器。为了方便起见，一些函数将始终返回 `NULL` 指针，以便用于 `return` 语句。

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

  这是设置错误指示器最常用的方法。第一个参数指定异常类型；它通常是标准异常之一，e.g. `PyExc_RuntimeError`。你不需要增加它的引用计数。第二个参数是错误信息，它解码自 `'utf-8'`。

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

  此函数类似于 `PyErr_SetString()`，但是允许你为异常的“值”指定任意一个 Python 对象。

PyObject* `PyErr_Format`(PyObject *exception, const char *format, ...)
  Return value: Always NULL.

  这个函数设置了一个错误指示器并且返回了 `NULL`，exception 应当是一个 Python 中的异常类。format 和随后的形参会帮助格式化这个错误的信息；它们与 `PyUnicode_FromFormat()` 有着相同的含义和值。format 是一个ASCII编码的字符串。

PyObject* `PyErr_FormatV`(PyObject *exception, const char *format, va_list vargs)
  Return value: Always NULL.

  和 `PyErr_Format()` 相同，但它接受一个 `va_list` 类型的参数而不是可变数量的参数集。

  3.5 版新加入.

void `PyErr_SetNone`(PyObject *type)

  这是 `PyErr_SetObject(type, Py_None)` 的简写。

int `PyErr_BadArgument`()

  这是 `PyErr_SetString(PyExc_TypeError, message)` 的简写，其中 message 指出使用了非法参数调用内置操作。它主要用于内部使用。

PyObject* `PyErr_NoMemory`()
  Return value: Always NULL.

  这是 `PyErr_SetNone(PyExc_MemoryError)` 的简写；它返回 `NULL` ，以便当内存耗尽时，对象分配函数可以写 `return PyErr_NoMemory();` 。

PyObject* `PyErr_SetFromErrno`(PyObject *type)
  Return value: Always NULL.

  这是个便捷函数，当 C 库函数返回错误并设置 `errno` 时，这个函数会触发异常。它构造一个元组对象，其第一项是整数值 `errno`，第二项是相应的错误消息（从 `strerror()` 获取），然后调用 `PyErr_SetObject(type, object)`。在 Unix 上，当 `errno` 值是 `EINTR` ，即中断的系统调用时，这个函数会调用 `PyErr_CheckSignals()` ，如果设置了错误指示器，则将其设置为该值。该函数永远返回 `NULL` ，因此当系统调用返回错误时，围绕系统调用的包装函数可以写成 `return PyErr_SetFromErrno(type);`。

PyObject* `PyErr_SetFromErrnoWithFilenameObject`(PyObject *type, PyObject *filenameObject)
  Return value: Always NULL.

  类似于 `PyErr_SetFromErrno()` ，附加的行为是如果 filenameObject 不为 `NULL` ，它将作为第三个参数传递给 type 的构造函数。举个例子，在 `OSError` 异常中，filenameObject 将用来定义异常实例的 `filename` 属性。

PyObject* `PyErr_SetFromErrnoWithFilenameObjects`(PyObject *type, PyObject *filenameObject, PyObject *filenameObject2)
  Return value: Always NULL.

  类似于 `PyErr_SetFromErrnoWithFilenameObject()` ，但接受第二个 filename 对象，用于当一个接受两个 filename 的函数失败时触发错误。

  3.4 版新加入.

PyObject* `PyErr_SetFromErrnoWithFilename`(PyObject *type, const char *filename)
  Return value: Always NULL.

  类似于 `PyErr_SetFromErrnoWithFilenameObject()` ，但文件名以 C 字符串形式给出。 filename 是从文件系统编码（`os.fsdecode()`）解码出来的。

PyObject* `PyErr_SetFromWindowsErr`(int ierr)
  Return value: Always NULL.

  这是触发 `WindowsError` 的便捷函数。如果 lerr 为 `0` ，则改用调用 `GetLastError()` 返回的错误代码。它调用 Win32 函数 `FormatMessage()` 来检索 ierr 或 `GetLastError()` 给定的错误代码的 Windows 描述，然后构造一个元组对象，其第一项是 ierr 值，第二项是相应的错误信息（从 `FormatMessage()` 获取），然后调用 `PyErr_SetObject(PyExc_WindowsError, object)` 。该函数永远返回 `NULL` 。

  可用性: Windows。

PyObject* `PyErr_SetExcFromWindowsErr`(PyObject *type, int ierr)
  Return value: Always NULL.

  类似于 `PyErr_SetFromWindowsErr()` ，额外的参数指定要触发的异常类型。

  可用性: Windows。

PyObject* `PyErr_SetFromWindowsErrWithFilename`(int ierr, const char *filename)
  Return value: Always NULL.

  类似于 `PyErr_SetFromWindowsErrWithFilenameObject()` ，但是 filename 是以 C 字符串形式给出的。 filename 是从文件系统编码（`os.fsdecode()`）解码出来的。

  可用性: Windows。

PyObject* `PyErr_SetExcFromWindowsErrWithFilenameObject`(PyObject *type, int ierr, PyObject *filename)
  Return value: Always NULL.

  类似于 `PyErr_SetFromWindowsErrWithFilenameObject()` ，额外参数指定要触发的异常类型。

  可用性: Windows。

PyObject* `PyErr_SetExcFromWindowsErrWithFilenameObjects`(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)
  Return value: Always NULL.

  类似于 `PyErr_SetExcFromWindowsErrWithFilenameObject()` ，但是接受第二个 filename 对象。

  可用性: Windows。

  3.4 版新加入.

PyObject* `PyErr_SetExcFromWindowsErrWithFilename`(PyObject *type, int ierr, const char *filename)
  Return value: Always NULL.

  类似于 `PyErr_SetFromWindowsErrWithFilename()` ，额外参数指定要触发的异常类型。

  可用性: Windows。

PyObject* `PyErr_SetImportError`(PyObject *msg, PyObject *name, PyObject *path)
  Return value: Always NULL.

  这是触发 `ImportError` 的便捷函数。 msg 将被设为异常的消息字符串。 name 和 path ，（都可以为 `NULL` ），将用来被设置 `ImportError` 对应的属性 `name` 和 `path`。

  3.3 版新加入.

void `PyErr_SyntaxLocationObject`(PyObject *filename, int lineno, int col_offset)

  设置当前异常的文件，行和偏移信息。如果当前异常不是 `SyntaxError` ，则它设置额外的属性，使异常打印子系统认为异常是 `SyntaxError`。

  3.4 版新加入.

void `PyErr_SyntaxLocationEx`(const char *filename, int lineno, int col_offset)

  与 `PyErr_SyntaxLocationObject()` 类似，只是 filename 是从文件系统编码（ `os.fsdecode()` ）解码出的一个字节字符串。

  3.2 版新加入.

void `PyErr_SyntaxLocation`(const char *filename, int lineno)

  与 `PyErr_SyntaxLocationEx()` 类似，但省略了参数 col_offset。

void `PyErr_BadInternalCall`()

  这是 `PyErr_SetString(PyExc_SystemError, message)` 的缩写，其中 message 表示使用了非法参数调用内部操作（例如，Python/C API 函数）。它主要用于内部使用。

## 发出警告

这些函数可以从 C 代码中发出警告。它们仿照了由 Python 模块 `warnings` 导出的那些函数。它们通常向 sys.stderr 打印一条警告信息；当然，用户也有可能已经指定将警告转换为错误，在这种情况下，它们将触发异常。也有可能由于警告机制出现问题，使得函数触发异常。如果没有触发异常，返回值为 `0` ；如果触发异常，返回值为 `-1`。（无法确定是否实际打印了警告信息，也无法确定异常触发的原因。这是故意为之）。如果触发了异常，调用者应该进行正常的异常处理（例如，`Py_DECREF()` 持有引用并返回一个错误值）。

int `PyErr_WarnEx`(PyObject *category, const char *message, Py_ssize_t stack_level)

  发出一个警告信息。参数 category 是一个警告类别（见下面）或 `NULL` ； message 是一个 UTF-8 编码的字符串。 stack_level 是一个给出栈帧数量的正数；警告将从该栈帧中当前正在执行的代码行发出。 stack_level 为 1 的是调用 `PyErr_WarnEx()` 的函数，2 是在此之上的函数，以此类推。

  警告类别必须是 `PyExc_Warning` 的子类， `PyExc_Warning` 是 `PyExc_Exception` 的子类；默认警告类别是 `PyExc_RuntimeWarning` 。标准 Python 警告类别作为全局变量可用，所有其名称见 标准警告类别 。

  有关警告控制的信息，参见模块文档 `warnings` 和命令行文档中的 `-W` 选项。没有用于警告控制的 C API。

PyObject* `PyErr_SetImportErrorSubclass`(PyObject *exception, PyObject *msg, PyObject *name, PyObject *path)
  Return value: Always NULL.

  Much like `PyErr_SetImportError()` but this function allows for specifying a subclass of `ImportError` to raise.

  3.6 版新加入.

int `PyErr_WarnExplicitObject`(PyObject *category, PyObject *message, PyObject *filename, int lineno, PyObject *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.

  3.4 版新加入.

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

  Similar to `PyErr_WarnExplicitObject()` except that message and module are UTF-8 encoded strings, and filename is decoded from the filesystem encoding (`os.fsdecode()`).

int `PyErr_WarnFormat`(PyObject *category, Py_ssize_t stack_level, const char *format, ...)

  Function similar to `PyErr_WarnEx()`, but use `PyUnicode_FromFormat()` to format the warning message. format is an ASCII-encoded string.

  3.2 版新加入.

int `PyErr_ResourceWarning`(PyObject *source, Py_ssize_t stack_level, const char *format, ...)

  Function similar to `PyErr_WarnFormat()`, but category is `ResourceWarning` and it passes source to `warnings.WarningMessage()`.

  3.6 版新加入.

## 查询错误指示器

PyObject* `PyErr_Occurred`()
  Return value: Borrowed reference.

  Test whether the error indicator is set. If set, return the exception type (the first argument to the last call to one of the `PyErr_Set*()` functions or to `PyErr_Restore()`). If not set, return `NULL`. You do not own a reference to the return value, so you do not need to `Py_DECREF()` it.

  The caller must hold the GIL.

  備註

  Do not compare the return value to a specific exception; use `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 be a subclass of the expected exception.)

int `PyErr_ExceptionMatches`(PyObject *exc)

  Equivalent to `PyErr_GivenExceptionMatches(PyErr_Occurred(), exc)`. This should only be called when an exception is actually set; a memory access violation will occur if no exception has been raised.

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

  Return true if the given exception matches the exception type in exc. If exc is a class object, this also returns true when given is an instance of a subclass. If exc is a tuple, all exception types in the tuple (and recursively in subtuples) are searched for a match.

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.

  備註

  This function is normally only used by code that needs to catch exceptions or by code that needs to save and restore the error indicator temporarily, e.g.:

      {
         PyObject *type, *value, *traceback;
         PyErr_Fetch(&type, &value, &traceback);

         /* ... code that might produce other errors ... */

         PyErr_Restore(type, value, traceback);
      }

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.)

  備註

  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 error indicator.

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

  Under certain circumstances, the values returned by `PyErr_Fetch()` below can be "unnormalized", meaning that `*exc` is a class object but `*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.

  備註

  This function does not implicitly set the `__traceback__` attribute on the exception value. If setting the traceback appropriately is desired, the following additional snippet is needed:

      if (tb != NULL) {
        PyException_SetTraceback(val, tb);
      }

void `PyErr_GetExcInfo`(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)

  Retrieve the exception info, as known from `sys.exc_info()`. This refers to an exception that was already caught, not to an exception that was freshly raised. Returns new references for the three objects, any of which may be `NULL`. Does not modify the exception info state.

  備註

  This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use `PyErr_SetExcInfo()` to restore or clear the exception state.

  3.3 版新加入.

void `PyErr_SetExcInfo`(PyObject *type, PyObject *value, PyObject *traceback)

  Set the exception info, as known from `sys.exc_info()`. This refers to an exception that was already caught, not to an exception that was freshly raised. This function steals the references of the arguments. To clear the exception state, pass `NULL` for all three arguments. For general rules about the three arguments, see `PyErr_Restore()`.

  備註

  This function is not normally used by code that wants to handle exceptions. Rather, it can be used when code needs to save and restore the exception state temporarily. Use `PyErr_GetExcInfo()` to read the exception state.

  3.3 版新加入.

## Signal Handling

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`; otherwise the function returns `0`. The error indicator may or may not be cleared if it was previously set.

void `PyErr_SetInterrupt`()

  Simulate the effect of a `SIGINT` signal arriving. The next time `PyErr_CheckSignals()` is called, the Python signal handler for `SIGINT` will be called.

  If `SIGINT` isn't handled by Python (it was set to `signal.SIG_DFL` or `signal.SIG_IGN`), this function does nothing.

int `PySignal_SetWakeupFd`(int fd)

  This utility function specifies a file descriptor to which the signal number is written as a single byte whenever a signal is received. fd must be non-blocking. 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.

  3.5 版更變: 在 Windows 上，此函数现在也支持套接字处理。

## Exception 类

PyObject* `PyErr_NewException`(const char *name, PyObject *base, PyObject *dict)
  Return value: New reference.

  This utility function creates and returns a new exception class. The name argument must be the name of the new exception, a C string of the form `module.classname`. The base and dict arguments are normally `NULL`. This creates a class object derived from `Exception` (accessible in C as `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`(const char *name, const char *doc, PyObject *base, PyObject *dict)
  Return value: New reference.

  Same as `PyErr_NewException()`, except that the new exception class can easily be given a docstring: If doc is non-`NULL`, it will be used as the docstring for the exception class.

  3.2 版新加入.

## 异常对象

PyObject* `PyException_GetTraceback`(PyObject *ex)
  Return value: New reference.

  Return the traceback associated with the exception as a new reference, as accessible from Python through `__traceback__`. If there is no traceback associated, this returns `NULL`.

int `PyException_SetTraceback`(PyObject *ex, PyObject *tb)

  Set the traceback associated with the exception to tb. Use `Py_None` to clear it.

PyObject* `PyException_GetContext`(PyObject *ex)
  Return value: New reference.

  Return the context (another exception instance during whose handling ex was raised) associated with the exception as a new reference, as accessible from Python through `__context__`. If there is no context associated, this returns `NULL`.

void `PyException_SetContext`(PyObject *ex, PyObject *ctx)

  Set the context associated with the exception to ctx. Use `NULL` to clear it. There is no type check to make sure that ctx is an exception instance. This steals a reference to ctx.

PyObject* `PyException_GetCause`(PyObject *ex)
  Return value: New reference.

  Return the cause (either an exception instance, or `None`, set by `raise ... from ...`) associated with the exception as a new reference, as accessible from Python through `__cause__`.

void `PyException_SetCause`(PyObject *ex, PyObject *cause)

  Set the cause associated with the exception to cause. Use `NULL` to clear it. There is no type check to make sure that cause is either an exception instance or `None`. This steals a reference to cause.

  `__suppress_context__` is implicitly set to `True` by this function.

## 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)
  Return value: New reference.

  Create a `UnicodeDecodeError` object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.

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)
  Return value: New reference.

  Create a `UnicodeEncodeError` object with the attributes encoding, object, length, start, end and reason. encoding and reason are UTF-8 encoded strings.

  3.3 版後已棄用: 3.11

  `Py_UNICODE` is deprecated since Python 3.3. Please migrate to `PyObject_CallFunction(PyExc_UnicodeEncodeError, "sOnns", ...)`.

PyObject* `PyUnicodeTranslateError_Create`(const Py_UNICODE *object, Py_ssize_t length, Py_ssize_t start, Py_ssize_t end, const char *reason)
  Return value: New reference.

  Create a `UnicodeTranslateError` object with the attributes object, length, start, end and reason. reason is a UTF-8 encoded string.

  3.3 版後已棄用: 3.11

  `Py_UNICODE` is deprecated since Python 3.3. Please migrate to `PyObject_CallFunction(PyExc_UnicodeTranslateError, "Onns", ...)`.

PyObject* `PyUnicodeDecodeError_GetEncoding`(PyObject *exc)
PyObject* `PyUnicodeEncodeError_GetEncoding`(PyObject *exc)
  Return value: New reference.

  Return the encoding attribute of the given exception object.

PyObject* `PyUnicodeDecodeError_GetObject`(PyObject *exc)
PyObject* `PyUnicodeEncodeError_GetObject`(PyObject *exc)
PyObject* `PyUnicodeTranslateError_GetObject`(PyObject *exc)
  Return value: New reference.

  Return the object attribute of the given exception object.

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)

  Get the start attribute of the given exception object and place it into *start. start must not be `NULL`. Return `0` on success, `-1` on failure.

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)

  Set the start attribute of the given exception object to start. Return `0` on success, `-1` on failure.

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)

  Get the end attribute of the given exception object and place it into *end. end must not be `NULL`. Return `0` on success, `-1` on failure.

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)

  Set the end attribute of the given exception object to end. Return `0` on success, `-1` on failure.

PyObject* `PyUnicodeDecodeError_GetReason`(PyObject *exc)
PyObject* `PyUnicodeEncodeError_GetReason`(PyObject *exc)
PyObject* `PyUnicodeTranslateError_GetReason`(PyObject *exc)
  Return value: New reference.

  返回给定异常对象的 reason 属性

int `PyUnicodeDecodeError_SetReason`(PyObject *exc, const char *reason)
int `PyUnicodeEncodeError_SetReason`(PyObject *exc, const char *reason)
int `PyUnicodeTranslateError_SetReason`(PyObject *exc, const char *reason)

  Set the reason attribute of the given exception object to reason. Return `0` on success, `-1` on failure.

## 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). They are also not needed for tp_call implementations because the call protocol takes care of recursion handling.

int `Py_EnterRecursiveCall`(const char *where)

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

  If `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 `RecursionError` is set and a nonzero value is returned. Otherwise, zero is returned.

  where should be a UTF-8 encoded string such as `" in instance check"` to be concatenated to the `RecursionError` message caused by the recursion depth limit.

  3.9 版更變: This function is now also available in the limited API.

void `Py_LeaveRecursiveCall`(void)

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

  3.9 版更變: This function is now also available in the limited API.

Properly implementing `tp_repr` for container types requires special recursion handling. In addition to protecting the stack, `tp_repr` also needs to track objects to prevent cycles. The following two functions facilitate this functionality. Effectively, these are the C equivalent to `reprlib.recursive_repr()`.

int `Py_ReprEnter`(PyObject *object)

  Called at the beginning of the `tp_repr` implementation to detect cycles.

  If the object has already been processed, the function returns a positive integer. In that case the `tp_repr` implementation should return a string object indicating a cycle. As examples, `dict` objects return `{...}` and `list` objects return `[...]`.

  The function will return a negative integer if the recursion limit is reached. In that case the `tp_repr` implementation should typically return `NULL`.

  Otherwise, the function returns zero and the `tp_repr` implementation can continue normally.

void `Py_ReprLeave`(PyObject *object)

  Ends a `Py_ReprEnter()`. Must be called once for each invocation of `Py_ReprEnter()` that returns zero.

## 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 | 註解
--- | --- | ---
`PyExc_BaseException` | `BaseException` | (1)
`PyExc_Exception` | `Exception` | (1)
`PyExc_ArithmeticError` | `ArithmeticError` | (1)
`PyExc_AssertionError` | `AssertionError` |
`PyExc_AttributeError` | `AttributeError` |
`PyExc_BlockingIOError` | `BlockingIOError` |
`PyExc_BrokenPipeError` | `BrokenPipeError` |
`PyExc_BufferError` | `BufferError` |
`PyExc_ChildProcessError` | `ChildProcessError` |
`PyExc_ConnectionAbortedError` | `ConnectionAbortedError` |
`PyExc_ConnectionError` | `ConnectionError` |
`PyExc_ConnectionRefusedError` | `ConnectionRefusedError` |
`PyExc_ConnectionResetError` | `ConnectionResetError` |
`PyExc_EOFError` | `EOFError` |
`PyExc_FileExistsError` | `FileExistsError` |
`PyExc_FileNotFoundError` | `FileNotFoundError` |
`PyExc_FloatingPointError` | `FloatingPointError` |
`PyExc_GeneratorExit` | `GeneratorExit` |
`PyExc_ImportError` | `ImportError` |
`PyExc_IndentationError` | `IndentationError` |
`PyExc_IndexError` | `IndexError` |
`PyExc_InterruptedError` | `InterruptedError` |
`PyExc_IsADirectoryError` | `IsADirectoryError` |
`PyExc_KeyError` | `KeyError` |
`PyExc_KeyboardInterrupt` | `KeyboardInterrupt` |
`PyExc_LookupError` | `LookupError` | (1)
`PyExc_MemoryError` | `MemoryError` |
`PyExc_ModuleNotFoundError` | `ModuleNotFoundError` |
`PyExc_NameError` | `NameError` |
`PyExc_NotADirectoryError` | `NotADirectoryError` |
`PyExc_NotImplementedError` | `NotImplementedError` |
`PyExc_OSError` | `OSError` | (1)
`PyExc_OverflowError` | `OverflowError` |
`PyExc_PermissionError` | `PermissionError` |
`PyExc_ProcessLookupError` | `ProcessLookupError` |
`PyExc_RecursionError` | `RecursionError` |
`PyExc_ReferenceError` | `ReferenceError` | (2)
`PyExc_RuntimeError` | `RuntimeError` |
`PyExc_StopAsyncIteration` | `StopAsyncIteration` |
`PyExc_StopIteration` | `StopIteration` |
`PyExc_SyntaxError` | `SyntaxError` |
`PyExc_SystemError` | `SystemError` |
`PyExc_SystemExit` | `SystemExit` |
`PyExc_TabError` | `TabError` |
`PyExc_TimeoutError` | `TimeoutError` |
`PyExc_TypeError` | `TypeError` |
`PyExc_UnboundLocalError` | `UnboundLocalError` |
`PyExc_UnicodeDecodeError` | `UnicodeDecodeError` |
`PyExc_UnicodeEncodeError` | `UnicodeEncodeError` |
`PyExc_UnicodeError` | `UnicodeError` |
`PyExc_UnicodeTranslateError` | `UnicodeTranslateError` |
`PyExc_ValueError` | `ValueError` |
`PyExc_ZeroDivisionError` | `ZeroDivisionError` |

3.3 版新加入: `PyExc_BlockingIOError`, `PyExc_BrokenPipeError`, `PyExc_ChildProcessError`, `PyExc_ConnectionError`, `PyExc_ConnectionAbortedError`, `PyExc_ConnectionRefusedError`, `PyExc_ConnectionResetError`, `PyExc_FileExistsError`, `PyExc_FileNotFoundError`, `PyExc_InterruptedError`, `PyExc_IsADirectoryError`, `PyExc_NotADirectoryError`, `PyExc_PermissionError`, `PyExc_ProcessLookupError` and `PyExc_TimeoutError` 介绍如下 PEP 3151.

3.5 版新加入: `PyExc_StopAsyncIteration` 和 `PyExc_RecursionError`.

3.6 版新加入: `PyExc_ModuleNotFoundError`.

这些是兼容性别名 `PyExc_OSError`:

C 名称 | 註解
--- | ---
`PyExc_EnvironmentError` |
`PyExc_IOError` |
`PyExc_WindowsError` | (3)

3.3 版更變: 这些别名曾经是单独的异常类型。

註解：

1. 这是其他标准异常的基类。

2. Only defined on Windows; protect code that uses this by testing that the preprocessor macro `MS_WINDOWS` is defined.

## 标准警告类别

All 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. For completeness, here are all the variables:

C 名称 | Python 名称 | 註解
--- | --- | ---
`PyExc_Warning` | `Warning` | (1)
`PyExc_BytesWarning` | `BytesWarning` |
`PyExc_DeprecationWarning` | `DeprecationWarning` |
`PyExc_FutureWarning` | `FutureWarning` |
`PyExc_ImportWarning` | `ImportWarning` |
`PyExc_PendingDeprecationWarning` | `PendingDeprecationWarning` |
`PyExc_ResourceWarning` | `ResourceWarning` |
`PyExc_RuntimeWarning` | `RuntimeWarning` |
`PyExc_SyntaxWarning` | `SyntaxWarning` |
`PyExc_UnicodeWarning` | `UnicodeWarning` |
`PyExc_UserWarning` | `UserWarning` |

3.2 版新加入: `PyExc_ResourceWarning`.

註解：

1. 这是其他标准警告类别的基类。