summaryrefslogtreecommitdiffstats
path: root/Doc/c-api/exceptions.rst
blob: fdd24dab2702dada97ab72428c0f57254c6242b1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
.. highlightlang:: c


.. _exceptionhandling:

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

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.

The error indicator consists of three Python objects corresponding to the result
of ``sys.exc_info()``.  API functions exist to interact with the error indicator
in various ways.  There is a separate error indicator for each thread.

.. XXX Order of these should be more thoughtful.
   Either alphabetical or some kind of structure.


.. c:function:: void PyErr_PrintEx(int set_sys_last_vars)

   Print a standard traceback to ``sys.stderr`` and clear the error indicator.
   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 :data:`sys.last_type`,
   :data:`sys.last_value` and :data:`sys.last_traceback` will be set to the
   type, value and traceback of the printed exception, respectively.


.. c:function:: void PyErr_Print()

   Alias for ``PyErr_PrintEx(1)``.


.. c:function:: PyObject* PyErr_Occurred()

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

   .. note::

      Do not compare the return value to a specific exception; use
      :c:func:`PyErr_ExceptionMatches` instead, shown below.  (The comparison could
      easily fail since the exception may be an instance instead of a class, in the
      case of a class exception, or it may the a subclass of the expected exception.)


.. c:function:: 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.


.. c:function:: int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)

   Return true if the *given* exception matches the exception 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 exceptions in the tuple (and
   recursively in subtuples) are searched for a match.


.. c:function:: void PyErr_NormalizeException(PyObject**exc, PyObject**val, PyObject**tb)

   Under certain circumstances, the values returned by :c:func:`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.


.. c:function:: void PyErr_Clear()

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


.. c:function:: 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.

   .. note::

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


.. c:function:: 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.)

   .. note::

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


.. c:function:: void PyErr_SetString(PyObject *type, const char *message)

   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. :c:data:`PyExc_RuntimeError`.  You need not increment its reference count.
   The second argument is an error message; it is decoded from ``'utf-8``'.


.. c:function:: void PyErr_SetObject(PyObject *type, PyObject *value)

   This function is similar to :c:func:`PyErr_SetString` but lets you specify an
   arbitrary Python object for the "value" of the exception.


.. c:function:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)

   This function sets the error indicator and returns *NULL*. *exception* should be
   a Python exception (class, not an instance). *format* should be an ASCII-encoded string,
   containing format codes, similar to :c:func:`printf`. The ``width.precision``
   before a format code is parsed, but the width part is ignored.

   .. % This should be exactly the same as the table in PyString_FromFormat.
   .. % One should just refer to the other.
   .. % The descriptions for %zd and %zu are wrong, but the truth is complicated
   .. % because not all compilers support the %z width modifier -- we fake it
   .. % when necessary via interpolating PY_FORMAT_SIZE_T.
   .. % Similar comments apply to the %ll width modifier and
   .. % PY_FORMAT_LONG_LONG.

   +-------------------+---------------+--------------------------------+
   | Format Characters | Type          | Comment                        |
   +===================+===============+================================+
   | :attr:`%%`        | *n/a*         | The literal % character.       |
   +-------------------+---------------+--------------------------------+
   | :attr:`%c`        | int           | A single character,            |
   |                   |               | represented as an C int.       |
   +-------------------+---------------+--------------------------------+
   | :attr:`%d`        | int           | Exactly equivalent to          |
   |                   |               | ``printf("%d")``.              |
   +-------------------+---------------+--------------------------------+
   | :attr:`%u`        | unsigned int  | Exactly equivalent to          |
   |                   |               | ``printf("%u")``.              |
   +-------------------+---------------+--------------------------------+
   | :attr:`%ld`       | long          | Exactly equivalent to          |
   |                   |               | ``printf("%ld")``.             |
   +-------------------+---------------+--------------------------------+
   | :attr:`%lu`       | unsigned long | Exactly equivalent to          |
   |                   |               | ``printf("%lu")``.             |
   +-------------------+---------------+--------------------------------+
   | :attr:`%lld`      | long long     | Exactly equivalent to          |
   |                   |               | ``printf("%lld")``.            |
   +-------------------+---------------+--------------------------------+
   | :attr:`%llu`      | unsigned      | Exactly equivalent to          |
   |                   | long long     | ``printf("%llu")``.            |
   +-------------------+---------------+--------------------------------+
   | :attr:`%zd`       | Py_ssize_t    | Exactly equivalent to          |
   |                   |               | ``printf("%zd")``.             |
   +-------------------+---------------+--------------------------------+
   | :attr:`%zu`       | size_t        | Exactly equivalent to          |
   |                   |               | ``printf("%zu")``.             |
   +-------------------+---------------+--------------------------------+
   | :attr:`%i`        | int           | Exactly equivalent to          |
   |                   |               | ``printf("%i")``.              |
   +-------------------+---------------+--------------------------------+
   | :attr:`%x`        | int           | Exactly equivalent to          |
   |                   |               | ``printf("%x")``.              |
   +-------------------+---------------+--------------------------------+
   | :attr:`%s`        | char\*        | A null-terminated C character  |
   |                   |               | array.                         |
   +-------------------+---------------+--------------------------------+
   | :attr:`%p`        | void\*        | The hex representation of a C  |
   |                   |               | pointer. Mostly equivalent to  |
   |                   |               | ``printf("%p")`` except that   |
   |                   |               | it is guaranteed to start with |
   |                   |               | the literal ``0x`` regardless  |
   |                   |               | of what the platform's         |
   |                   |               | ``printf`` yields.             |
   +-------------------+---------------+--------------------------------+

   An unrecognized format character causes all the rest of the format string to be
   copied as-is to the result string, and any extra arguments discarded.

   .. note::

      The `"%lld"` and `"%llu"` format specifiers are only available
      when :const:`HAVE_LONG_LONG` is defined.

   .. versionchanged:: 3.2
      Support for `"%lld"` and `"%llu"` added.


.. c:function:: void PyErr_SetNone(PyObject *type)

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


.. c:function:: int PyErr_BadArgument()

   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.


.. c:function:: PyObject* PyErr_NoMemory()

   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.


.. c:function:: PyObject* PyErr_SetFromErrno(PyObject *type)

   .. index:: single: strerror()

   This is a convenience function to raise an exception when a C library function
   has returned an error and set the C variable :c:data:`errno`.  It constructs a
   tuple object whose first item is the integer :c:data:`errno` value and whose
   second item is the corresponding error message (gotten from :c:func:`strerror`),
   and then calls ``PyErr_SetObject(type, object)``.  On Unix, when the
   :c:data:`errno` value is :const:`EINTR`, indicating an interrupted system call,
   this calls :c:func:`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.


.. c:function:: PyObject* PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)

   Similar to :c:func:`PyErr_SetFromErrno`, with the additional behavior that if
   *filename* is not *NULL*, it is passed to the constructor of *type* as a third
   parameter.  In the case of exceptions such as :exc:`IOError` and :exc:`OSError`,
   this is used to define the :attr:`filename` attribute of the exception instance.
   *filename* is decoded from the filesystem encoding
   (:func:`sys.getfilesystemencoding`).


.. c:function:: PyObject* PyErr_SetFromWindowsErr(int ierr)

   This is a convenience function to raise :exc:`WindowsError`. If called with
   *ierr* of :c:data:`0`, the error code returned by a call to :c:func:`GetLastError`
   is used instead.  It calls the Win32 function :c:func:`FormatMessage` to retrieve
   the Windows description of error code given by *ierr* or :c:func:`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
   :c:func:`FormatMessage`), and then calls ``PyErr_SetObject(PyExc_WindowsError,
   object)``. This function always returns *NULL*. Availability: Windows.


.. c:function:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)

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


.. c:function:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)

   Similar to :c:func:`PyErr_SetFromWindowsErr`, with the additional behavior that
   if *filename* is not *NULL*, it is passed to the constructor of
   :exc:`WindowsError` as a third parameter. Availability: Windows.


.. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, char *filename)

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


.. c:function:: void PyErr_SyntaxLocationEx(char *filename, int lineno, int col_offset)

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

.. versionadded:: 3.2


.. c:function:: void PyErr_SyntaxLocation(char *filename, int lineno)

   Like :c:func:`PyErr_SyntaxLocationExc`, but the col_offset parameter is
   omitted.


.. c:function:: void PyErr_BadInternalCall()

   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.


.. c:function:: int PyErr_WarnEx(PyObject *category, char *message, int stack_level)

   Issue a warning message.  The *category* argument is a warning category (see
   below) or *NULL*; the *message* argument is a message 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 :c:func:`PyErr_WarnEx`, 2 is  the function above that,
   and so forth.

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

   Warning categories must be subclasses of :c:data:`Warning`; the default warning
   category is :c:data:`RuntimeWarning`.  The standard Python warning categories are
   available as global variables whose names are ``PyExc_`` followed by the Python
   exception name. These have the type :c:type:`PyObject\*`; they are all class
   objects. Their names are :c:data:`PyExc_Warning`, :c:data:`PyExc_UserWarning`,
   :c:data:`PyExc_UnicodeWarning`, :c:data:`PyExc_DeprecationWarning`,
   :c:data:`PyExc_SyntaxWarning`, :c:data:`PyExc_RuntimeWarning`, and
   :c:data:`PyExc_FutureWarning`.  :c:data:`PyExc_Warning` is a subclass of
   :c:data:`PyExc_Exception`; the other warning categories are subclasses of
   :c:data:`PyExc_Warning`.

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


.. c:function:: int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)

   Issue a warning message with explicit control over all warning attributes.  This
   is a straightforward wrapper around the Python function
   :func:`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.


.. c:function:: int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)

   Function similar to :c:func:`PyErr_WarnEx`, but use
   :c:func:`PyUnicode_FromFormatV` to format the warning message.

   .. versionadded:: 3.2

.. c:function:: int PyErr_CheckSignals()

   .. index::
      module: signal
      single: SIGINT
      single: KeyboardInterrupt (built-in exception)

   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 :mod:`signal` module is supported, this can invoke a
   signal handler written in Python.  In all cases, the default effect for
   :const:`SIGINT` is to raise the  :exc:`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.


.. c:function:: void PyErr_SetInterrupt()

   .. index::
      single: SIGINT
      single: KeyboardInterrupt (built-in exception)

   This function simulates the effect of a :const:`SIGINT` signal arriving --- the
   next time :c:func:`PyErr_CheckSignals` is called,  :exc:`KeyboardInterrupt` will
   be raised.  It may be called without holding the interpreter lock.

   .. % XXX This was described as obsolete, but is used in
   .. % _thread.interrupt_main() (used from IDLE), so it's still needed.


.. c:function:: int PySignal_SetWakeupFd(int fd)

   This utility function specifies a file descriptor to which a ``'\0'`` byte will
   be written whenever a signal is received.  It returns the previous such file
   descriptor.  The value ``-1`` disables the feature; this is the initial state.
   This is equivalent to :func:`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.


.. c:function:: PyObject* PyErr_NewException(char *name, PyObject *base, PyObject *dict)

   This utility function creates and returns a new exception object. The *name*
   argument must be the name of the new exception, a C string of the form
   ``module.class``.  The *base* and *dict* arguments are normally *NULL*.  This
   creates a class object derived from :exc:`Exception` (accessible in C as
   :c:data:`PyExc_Exception`).

   The :attr:`__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.


.. c:function:: PyObject* PyErr_NewExceptionWithDoc(char *name, char *doc, PyObject *base, PyObject *dict)

   Same as :c:func:`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.

   .. versionadded:: 3.2


.. c:function:: void PyErr_WriteUnraisable(PyObject *obj)

   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
   :meth:`__del__` method.

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


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

.. c:function:: PyObject* PyException_GetTraceback(PyObject *ex)

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


.. c:function:: int PyException_SetTraceback(PyObject *ex, PyObject *tb)

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


.. c:function:: 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 :attr:`__context__`.  If there is no context associated, this
   returns *NULL*.


.. c:function:: 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*.


.. c:function:: PyObject* PyException_GetCause(PyObject *ex)

   Return the cause (another exception instance set by ``raise ... from ...``)
   associated with the exception as a new reference, as accessible from Python
   through :attr:`__cause__`.  If there is no cause associated, this returns
   *NULL*.


.. c:function:: void PyException_SetCause(PyObject *ex, PyObject *ctx)

   Set the cause 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*.


.. _unicodeexceptions:

Unicode Exception Objects
=========================

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

.. c:function:: 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 :class:`UnicodeDecodeError` object with the attributes *encoding*,
   *object*, *length*, *start*, *end* and *reason*.

.. c:function:: 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 :class:`UnicodeEncodeError` object with the attributes *encoding*,
   *object*, *length*, *start*, *end* and *reason*.

.. c:function:: PyObject* PyUnicodeTranslateError_Create(const Py_UNICODE *object, Py_ssize_t length, Py_ssize_t start, Py_ssize_t end, const char *reason)

   Create a :class:`UnicodeTranslateError` object with the attributes *object*,
   *length*, *start*, *end* and *reason*.

.. c:function:: PyObject* PyUnicodeDecodeError_GetEncoding(PyObject *exc)
                PyObject* PyUnicodeEncodeError_GetEncoding(PyObject *exc)

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

.. c:function:: PyObject* PyUnicodeDecodeError_GetObject(PyObject *exc)
                PyObject* PyUnicodeEncodeError_GetObject(PyObject *exc)
                PyObject* PyUnicodeTranslateError_GetObject(PyObject *exc)

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

.. c:function:: 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.

.. c:function:: 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.

.. c:function:: 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.

.. c:function:: 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.

.. c:function:: PyObject* PyUnicodeDecodeError_GetReason(PyObject *exc)
                PyObject* PyUnicodeEncodeError_GetReason(PyObject *exc)
                PyObject* PyUnicodeTranslateError_GetReason(PyObject *exc)

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

.. c:function:: 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.


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).

.. c:function:: int Py_EnterRecursiveCall(char *where)

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

   If :const:`USE_STACKCHECK` is defined, this function checks if the the OS
   stack overflowed using :c:func:`PyOS_CheckStack`.  In this is the case, it
   sets a :exc:`MemoryError` and returns a nonzero value.

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

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

.. c:function:: void Py_LeaveRecursiveCall()

   Ends a :c:func:`Py_EnterRecursiveCall`.  Must be called once for each
   *successful* invocation of :c:func:`Py_EnterRecursiveCall`.


.. _standardexceptions:

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
:c:type:`PyObject\*`; they are all class objects.  For completeness, here are all
the variables:

+-------------------------------------+----------------------------+----------+
| C Name                              | Python Name                | Notes    |
+=====================================+============================+==========+
| :c:data:`PyExc_BaseException`       | :exc:`BaseException`       | \(1)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_Exception`           | :exc:`Exception`           | \(1)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_ArithmeticError`     | :exc:`ArithmeticError`     | \(1)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_LookupError`         | :exc:`LookupError`         | \(1)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_AssertionError`      | :exc:`AssertionError`      |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_AttributeError`      | :exc:`AttributeError`      |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_EOFError`            | :exc:`EOFError`            |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_EnvironmentError`    | :exc:`EnvironmentError`    | \(1)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_FloatingPointError`  | :exc:`FloatingPointError`  |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_IOError`             | :exc:`IOError`             |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_ImportError`         | :exc:`ImportError`         |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_IndexError`          | :exc:`IndexError`          |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_KeyError`            | :exc:`KeyError`            |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_KeyboardInterrupt`   | :exc:`KeyboardInterrupt`   |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_MemoryError`         | :exc:`MemoryError`         |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_NameError`           | :exc:`NameError`           |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_NotImplementedError` | :exc:`NotImplementedError` |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_OSError`             | :exc:`OSError`             |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_OverflowError`       | :exc:`OverflowError`       |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_ReferenceError`      | :exc:`ReferenceError`      | \(2)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_RuntimeError`        | :exc:`RuntimeError`        |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_SyntaxError`         | :exc:`SyntaxError`         |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_SystemError`         | :exc:`SystemError`         |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_SystemExit`          | :exc:`SystemExit`          |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_TypeError`           | :exc:`TypeError`           |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_ValueError`          | :exc:`ValueError`          |          |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_WindowsError`        | :exc:`WindowsError`        | \(3)     |
+-------------------------------------+----------------------------+----------+
| :c:data:`PyExc_ZeroDivisionError`   | :exc:`ZeroDivisionError`   |          |
+-------------------------------------+----------------------------+----------+

.. index::
   single: PyExc_BaseException
   single: PyExc_Exception
   single: PyExc_ArithmeticError
   single: PyExc_LookupError
   single: PyExc_AssertionError
   single: PyExc_AttributeError
   single: PyExc_EOFError
   single: PyExc_EnvironmentError
   single: PyExc_FloatingPointError
   single: PyExc_IOError
   single: PyExc_ImportError
   single: PyExc_IndexError
   single: PyExc_KeyError
   single: PyExc_KeyboardInterrupt
   single: PyExc_MemoryError
   single: PyExc_NameError
   single: PyExc_NotImplementedError
   single: PyExc_OSError
   single: PyExc_OverflowError
   single: PyExc_ReferenceError
   single: PyExc_RuntimeError
   single: PyExc_SyntaxError
   single: PyExc_SystemError
   single: PyExc_SystemExit
   single: PyExc_TypeError
   single: PyExc_ValueError
   single: PyExc_WindowsError
   single: PyExc_ZeroDivisionError

Notes:

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

(2)
   This is the same as :exc:`weakref.ReferenceError`.

(3)
   Only defined on Windows; protect code that uses this by testing that the
   preprocessor macro ``MS_WINDOWS`` is defined.