# 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 POSIX `errno` variable: there is a global indicator (per thread) of the last error that occurred. Most C API functions don’t clear this on success, but will set it to indicate the cause of the error on failure. Most C API functions also return an error indicator, usually NULL if they are supposed to return a pointer, or `-1` if they return an integer (exception: the `PyArg_*()` functions return `1` for success and `0` for failure).

Concretely, the error indicator consists of three object pointers: the exception’s type, the exception’s value, and the traceback object. Any of those pointers can be NULL if non-set (although some combinations are forbidden, for example you can’t have a non-NULL traceback if the exception type is NULL).

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。

注解

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`()

  清楚错误指示器。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)

  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。

## 抛出异常

These functions help you set the current thread’s error indicator. For convenience, some of these functions will always return a NULL pointer for use in a `return` statement.

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`。你不务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.

  This function sets the error indicator and returns NULL. exception should be a Python exception class. The format and subsequent parameters help format the error message; they have the same meaning and values as in `PyUnicode_FromFormat()`. format is an ASCII-encoded string.

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 新版功能.

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.

  This is a shorthand for `PyErr_SetNone(PyExc_MemoryError)`; it returns NULL so an object allocation function can write `return PyErr_NoMemory();` when it runs out of memory.

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

  This is a convenience function to raise an exception when a C library function has returned an error and set the C variable `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)

  Similar to `PyErr_SetFromErrno()`, with the additional behavior that if filenameObject is not NULL, it is passed to the constructor of type as a third parameter. In the case of `OSError` exception, this is used to define the `filename` attribute of the exception instance.

PyObject* `PyErr_SetFromErrnoWithFilenameObjects`(PyObject *type, PyObject *filenameObject, PyObject *filenameObject2)

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

  3.4 新版功能.

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.

  This is a convenience function to raise `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)
  Return value: Always NULL.

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

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

  Similar to `PyErr_SetFromWindowsErrWithFilenameObject()`, but the filename is given as a C string. filename is decoded from the filesystem encoding (`os.fsdecode()`). Availability: Windows.

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

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

PyObject* `PyErr_SetExcFromWindowsErrWithFilenameObjects`(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)

  Similar to `PyErr_SetExcFromWindowsErrWithFilenameObject()`, but accepts a second filename object. Availability: Windows.

  3.4 新版功能.

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

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

PyObject* `PyErr_SetImportError`(PyObject *msg, PyObject *name, PyObject *path)

  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 新版功能.

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 新版功能.

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 新版功能.

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。

## 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)

  Issue a warning message. The category argument is a warning category (see below) or NULL; the message argument is a UTF-8 encoded string. stack_level 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 stack_level of 1 is the function calling `PyErr_WarnEx()`, 2 is the function above that, and so forth.

  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 *msg, PyObject *name, PyObject *path)

  和 `PyErr_SetImportError()` 很类似，但这个函数允许指定一个 `ImportError` 的子类来触发。

  3.6 新版功能.

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 新版功能.

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 新版功能.

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

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

  3.6 新版功能.

## 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.

  注解

  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.

  注解

  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.)

  注解

  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.

  注解

  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.

  注解

  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 新版功能.

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()`.

  注解

  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 新版功能.

## 信号处理

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`()

  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 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.

  在 3.5 版更改: 在 Windows 上，此函数现在也支持套接字处理。

## 异常类

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 新版功能.

## 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)

  将异常关联的回溯设置为 tb 。使用``Py_None``清除它。

PyObject* `PyException_GetContext`(PyObject *ex)

  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 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)

  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)

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

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

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

PyObject* `PyUnicodeDecodeError_GetEncoding`(PyObject *exc)
PyObject* `PyUnicodeEncodeError_GetEncoding`(PyObject *exc)

  返回给定异常对象的 encoding 属性

PyObject* `PyUnicodeDecodeError_GetObject`(PyObject *exc)
PyObject* `PyUnicodeEncodeError_GetObject`(PyObject *exc)
PyObject* `PyUnicodeTranslateError_GetObject`(PyObject *exc)

  返回给定异常对象的 object 属性

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)

  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).

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 string such as `" in instance check"` to be concatenated to the `RecursionError` 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()`.

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 | 注释
--- | --- | ---
`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 新版功能: `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 新版功能: `PyExc_StopAsyncIteration` 和 `PyExc_RecursionError`.

3.6 新版功能: `PyExc_ModuleNotFoundError`.

这些是兼容性别名 `PyExc_OSError`:

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

在 3.3 版更改: 这些别名曾经是单独的异常类型。

注释:

1. 这是其他标准异常的基类。

2. This is the same as `weakref.ReferenceError`.

3. 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 | 注释
--- | --- | ---
`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 新版功能: `PyExc_ResourceWarning`.

注释:

1. 这是其他标准警告类别的基类。