Exception Handling
******************

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").

When a function must fail because some function it called failed, it
generally doesn't set the error indicator; the function it called
already set it.  It is responsible for either handling the error and
clearing the exception or returning after cleaning up any resources it
holds (such as object references or memory allocations); it should
*not* continue normally if it is not prepared to handle the error.  If
returning due to an error, it is important to indicate to the caller
that an error has been set.  If the error is not handled or carefully
propagated, additional calls into the Python/C API may not behave as
intended and may fail in mysterious ways.

Note:

  The error indicator is **not** the result of "sys.exc_info()". The
  former corresponds to an exception that is not yet caught (and is
  therefore still propagating), while the latter returns an exception
  after it is caught (and has therefore stopped propagating).


Printing and clearing
=====================

void PyErr_Clear()
    * Part of the Stable ABI.*

   Clear the error indicator.  If the error indicator is not set,
   there is no effect.

void PyErr_PrintEx(int set_sys_last_vars)
    * Part of the Stable ABI.*

   Print a standard traceback to "sys.stderr" and clear the error
   indicator. **Unless** the error is a "SystemExit", in that case no
   traceback is printed and the Python process will exit with the
   error code specified by the "SystemExit" instance.

   Call this function **only** when the error indicator is set.
   Otherwise it will cause a fatal error!

   If *set_sys_last_vars* is nonzero, the variables "sys.last_type",
   "sys.last_value" and "sys.last_traceback" will be set to the type,
   value and traceback of the printed exception, respectively.

void PyErr_Print()
    * Part of the Stable ABI.*

   Alias for "PyErr_PrintEx(1)".

void PyErr_WriteUnraisable(PyObject *obj)
    * Part of the Stable ABI.*

   Call "sys.unraisablehook()" using the current exception and *obj*
   argument.

   This utility function prints a warning message to "sys.stderr" when
   an exception has been set but it is impossible for the interpreter
   to actually raise the exception.  It is used, for example, when an
   exception occurs in an "__del__()" method.

   The function is called with a single argument *obj* that identifies
   the context in which the unraisable exception occurred. If
   possible, the repr of *obj* will be printed in the warning message.

   An exception must be set when calling this function.


Raising exceptions
==================

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)
    * Part of the Stable ABI.*

   This is the most common way to set the error indicator.  The first
   argument specifies the exception type; it is normally one of the
   standard exceptions, e.g. "PyExc_RuntimeError".  You need not
   increment its reference count. The second argument is an error
   message; it is decoded from "'utf-8'".

void PyErr_SetObject(PyObject *type, PyObject *value)
    * Part of the Stable ABI.*

   This function is similar to "PyErr_SetString()" but lets you
   specify an arbitrary Python object for the "value" of the
   exception.

PyObject *PyErr_Format(PyObject *exception, const char *format, ...)
    *Return value: Always NULL.** Part of the Stable ABI.*

   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.** Part of the Stable ABI since version
   3.5.*

   Same as "PyErr_Format()", but taking a "va_list" argument rather
   than a variable number of arguments.

   New in version 3.5.

void PyErr_SetNone(PyObject *type)
    * Part of the Stable ABI.*

   This is a shorthand for "PyErr_SetObject(type, Py_None)".

int PyErr_BadArgument()
    * Part of the Stable ABI.*

   This is a shorthand for "PyErr_SetString(PyExc_TypeError,
   message)", where *message* indicates that a built-in operation was
   invoked with an illegal argument.  It is mostly for internal use.

PyObject *PyErr_NoMemory()
    *Return value: Always NULL.** Part of the Stable ABI.*

   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.** Part of the Stable ABI.*

   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)
    *Return value: Always NULL.** Part of the Stable ABI.*

   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)
    *Return value: Always NULL.** Part of the Stable ABI since version
   3.7.*

   Similar to "PyErr_SetFromErrnoWithFilenameObject()", but takes a
   second filename object, for raising errors when a function that
   takes two filenames fails.

   New in version 3.4.

PyObject *PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)
    *Return value: Always NULL.** Part of the Stable ABI.*

   Similar to "PyErr_SetFromErrnoWithFilenameObject()", but the
   filename is given as a C string.  *filename* is decoded from the
   *filesystem encoding and error handler*.

PyObject *PyErr_SetFromWindowsErr(int ierr)
    *Return value: Always NULL.** Part of the Stable ABI on Windows
   since version 3.7.*

   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.** Part of the Stable ABI on Windows
   since version 3.7.*

   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.** Part of the Stable ABI on Windows
   since version 3.7.*

   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)
    *Return value: Always NULL.** Part of the Stable ABI on Windows
   since version 3.7.*

   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)
    *Return value: Always NULL.** Part of the Stable ABI on Windows
   since version 3.7.*

   Similar to "PyErr_SetExcFromWindowsErrWithFilenameObject()", but
   accepts a second filename object.

   Availability: Windows.

   New in version 3.4.

PyObject *PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, const char *filename)
    *Return value: Always NULL.** Part of the Stable ABI on Windows
   since version 3.7.*

   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)
    *Return value: Always NULL.** Part of the Stable ABI since version
   3.7.*

   This is a convenience function to raise "ImportError". *msg* will
   be set as the exception's message string. *name* and *path*, both
   of which can be "NULL", will be set as the "ImportError"'s
   respective "name" and "path" attributes.

   New in version 3.3.

PyObject *PyErr_SetImportErrorSubclass(PyObject *exception, PyObject *msg, PyObject *name, PyObject *path)
    *Return value: Always NULL.** Part of the Stable ABI since version
   3.6.*

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

   New in version 3.6.

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

   Set file, line, and offset information for the current exception.
   If the current exception is not a "SyntaxError", then it sets
   additional attributes, which make the exception printing subsystem
   think the exception is a "SyntaxError".

   New in version 3.4.

void PyErr_SyntaxLocationEx(const char *filename, int lineno, int col_offset)
    * Part of the Stable ABI since version 3.7.*

   Like "PyErr_SyntaxLocationObject()", but *filename* is a byte
   string decoded from the *filesystem encoding and error handler*.

   New in version 3.2.

void PyErr_SyntaxLocation(const char *filename, int lineno)
    * Part of the Stable ABI.*

   Like "PyErr_SyntaxLocationEx()", but the *col_offset* parameter is
   omitted.

void PyErr_BadInternalCall()
    * Part of the Stable ABI.*

   This is a shorthand for "PyErr_SetString(PyExc_SystemError,
   message)", where *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.


Issuing warnings
================

Use these functions to issue warnings from C code.  They mirror
similar functions exported by the Python "warnings" module.  They
normally print 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 they will raise an exception.  It is
also possible that the functions raise an exception because of a
problem with the warning machinery. 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).

int PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)
    * Part of the Stable ABI.*

   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.

   Warning categories must be subclasses of "PyExc_Warning";
   "PyExc_Warning" is a subclass of "PyExc_Exception"; the default
   warning category is "PyExc_RuntimeWarning". The standard Python
   warning categories are available as global variables whose names
   are enumerated at Standard Warning Categories.

   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_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.

   New in version 3.4.

int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)
    * Part of the Stable ABI.*

   Similar to "PyErr_WarnExplicitObject()" except that *message* and
   *module* are UTF-8 encoded strings, and *filename* is decoded from
   the *filesystem encoding and error handler*.

int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)
    * Part of the Stable ABI.*

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

   New in version 3.2.

int PyErr_ResourceWarning(PyObject *source, Py_ssize_t stack_level, const char *format, ...)
    * Part of the Stable ABI since version 3.6.*

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

   New in version 3.6.


Querying the error indicator
============================

PyObject *PyErr_Occurred()
    *Return value: Borrowed reference.** Part of the Stable ABI.*

   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.

   Note:

     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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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.

   Note:

     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)
    * Part of the Stable ABI.*

   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.)

   Note:

     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)
    * Part of the Stable ABI.*

   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.

   Note:

     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);
        }

PyObject *PyErr_GetHandledException(void)
    * Part of the Stable ABI since version 3.11.*

   Retrieve the active exception instance, as would be returned by
   "sys.exception()". This refers to an exception that was *already
   caught*, not to an exception that was freshly raised. Returns a new
   reference to the exception or "NULL". Does not modify the
   interpreter's exception state.

   Note:

     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_SetHandledException()" to restore or clear the exception
     state.

   New in version 3.11.

void PyErr_SetHandledException(PyObject *exc)
    * Part of the Stable ABI since version 3.11.*

   Set the active exception, as known from "sys.exception()".  This
   refers to an exception that was *already caught*, not to an
   exception that was freshly raised. To clear the exception state,
   pass "NULL".

   Note:

     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_GetHandledException()" to get the exception state.

   New in version 3.11.

void PyErr_GetExcInfo(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
    * Part of the Stable ABI since version 3.7.*

   Retrieve the old-style representation of 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.  This function
   is kept for backwards compatibility. Prefer using
   "PyErr_GetHandledException()".

   Note:

     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.

   New in version 3.3.

void PyErr_SetExcInfo(PyObject *type, PyObject *value, PyObject *traceback)
    * Part of the Stable ABI since version 3.7.*

   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. This function is kept for backwards
   compatibility. Prefer using "PyErr_SetHandledException()".

   Note:

     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.

   New in version 3.3.

   Changed in version 3.11: The "type" and "traceback" arguments are
   no longer used and can be NULL. The interpreter now derives them
   from the exception instance (the "value" argument). The function
   still steals references of all three arguments.


Signal Handling
===============

int PyErr_CheckSignals()
    * Part of the Stable ABI.*

   This function interacts with Python's signal handling.

   If the function is called from the main thread and under the main
   Python interpreter, 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.

   The function attempts to handle all pending signals, and then
   returns "0". However, if a Python signal handler raises an
   exception, the error indicator is set and the function returns "-1"
   immediately (such that other pending signals may not have been
   handled yet: they will be on the next "PyErr_CheckSignals()"
   invocation).

   If the function is called from a non-main thread, or under a non-
   main Python interpreter, it does nothing and returns "0".

   This function can be called by long-running C code that wants to be
   interruptible by user requests (such as by pressing Ctrl-C).

   Note:

     The default Python signal handler for "SIGINT" raises the
     "KeyboardInterrupt" exception.

void PyErr_SetInterrupt()
    * Part of the Stable ABI.*

   Simulate the effect of a "SIGINT" signal arriving. This is
   equivalent to "PyErr_SetInterruptEx(SIGINT)".

   Note:

     This function is async-signal-safe.  It can be called without the
     *GIL* and from a C signal handler.

int PyErr_SetInterruptEx(int signum)
    * Part of the Stable ABI since version 3.10.*

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

   This function can be called by C code that sets up its own signal
   handling and wants Python signal handlers to be invoked as expected
   when an interruption is requested (for example when the user
   presses Ctrl-C to interrupt an operation).

   If the given signal isn't handled by Python (it was set to
   "signal.SIG_DFL" or "signal.SIG_IGN"), it will be ignored.

   If *signum* is outside of the allowed range of signal numbers, "-1"
   is returned.  Otherwise, "0" is returned.  The error indicator is
   never changed by this function.

   Note:

     This function is async-signal-safe.  It can be called without the
     *GIL* and from a C signal handler.

   New in version 3.10.

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.

   Changed in version 3.5: On Windows, the function now also supports
   socket handles.


Exception Classes
=================

PyObject *PyErr_NewException(const char *name, PyObject *base, PyObject *dict)
    *Return value: New reference.** Part of the Stable ABI.*

   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.** Part of the Stable ABI.*

   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.

   New in version 3.2.


Exception Objects
=================

PyObject *PyException_GetTraceback(PyObject *ex)
    *Return value: New reference.** Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

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

PyObject *PyException_GetContext(PyObject *ex)
    *Return value: New reference.** Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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.** Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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 Exception Objects
=========================

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.** Part of the Stable ABI.*

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

PyObject *PyUnicodeDecodeError_GetEncoding(PyObject *exc)
PyObject *PyUnicodeEncodeError_GetEncoding(PyObject *exc)
    *Return value: New reference.** Part of the Stable ABI.*

   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.** Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

   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.** Part of the Stable ABI.*

   Return the *reason* attribute of the given exception object.

int PyUnicodeDecodeError_SetReason(PyObject *exc, const char *reason)
int PyUnicodeEncodeError_SetReason(PyObject *exc, const char *reason)
int PyUnicodeTranslateError_SetReason(PyObject *exc, const char *reason)
    * Part of the Stable ABI.*

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


Recursion Control
=================

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)
    * Part of the Stable ABI since version 3.9.*

   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.

   Changed in version 3.9: This function is now also available in the
   limited API.

void Py_LeaveRecursiveCall(void)
    * Part of the Stable ABI since version 3.9.*

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

   Changed in version 3.9: 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)
    * Part of the Stable ABI.*

   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)
    * Part of the Stable ABI.*

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


Standard Exceptions
===================

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 Name                                    | Python Name                       | Notes      |
|===========================================|===================================|============|
| "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"                  |            |
+-------------------------------------------+-----------------------------------+------------+
| "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"               |            |
+-------------------------------------------+-----------------------------------+------------+

New in version 3.3: "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" were introduced following **PEP 3151**.

New in version 3.5: "PyExc_StopAsyncIteration" and
"PyExc_RecursionError".

New in version 3.6: "PyExc_ModuleNotFoundError".

These are compatibility aliases to "PyExc_OSError":

+---------------------------------------+------------+
| C Name                                | Notes      |
|=======================================|============|
| "PyExc_EnvironmentError"              |            |
+---------------------------------------+------------+
| "PyExc_IOError"                       |            |
+---------------------------------------+------------+
| "PyExc_WindowsError"                  | [2]        |
+---------------------------------------+------------+

Changed in version 3.3: These aliases used to be separate exception
types.

Notes:

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

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


Standard Warning Categories
===========================

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 Name                                     | Python Name                       | Notes      |
|============================================|===================================|============|
| "PyExc_Warning"                            | "Warning"                         | [3]        |
+--------------------------------------------+-----------------------------------+------------+
| "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"                     |            |
+--------------------------------------------+-----------------------------------+------------+

New in version 3.2: "PyExc_ResourceWarning".

Notes:

[3] This is a base class for other standard warning categories.
