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/Doc/c-api/exceptions.rst

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  1.. highlightlang:: c
  2
  3
  4.. _exceptionhandling:
  5
  6******************
  7Exception Handling
  8******************
  9
 10The functions described in this chapter will let you handle and raise Python
 11exceptions.  It is important to understand some of the basics of Python
 12exception handling.  It works somewhat like the Unix :cdata:`errno` variable:
 13there is a global indicator (per thread) of the last error that occurred.  Most
 14functions don't clear this on success, but will set it to indicate the cause of
 15the error on failure.  Most functions also return an error indicator, usually
 16*NULL* if they are supposed to return a pointer, or ``-1`` if they return an
 17integer (exception: the :cfunc:`PyArg_\*` functions return ``1`` for success and
 18``0`` for failure).
 19
 20When a function must fail because some function it called failed, it generally
 21doesn't set the error indicator; the function it called already set it.  It is
 22responsible for either handling the error and clearing the exception or
 23returning after cleaning up any resources it holds (such as object references or
 24memory allocations); it should *not* continue normally if it is not prepared to
 25handle the error.  If returning due to an error, it is important to indicate to
 26the caller that an error has been set.  If the error is not handled or carefully
 27propagated, additional calls into the Python/C API may not behave as intended
 28and may fail in mysterious ways.
 29
 30.. index::
 31   single: exc_type (in module sys)
 32   single: exc_value (in module sys)
 33   single: exc_traceback (in module sys)
 34
 35The error indicator consists of three Python objects corresponding to   the
 36Python variables ``sys.exc_type``, ``sys.exc_value`` and ``sys.exc_traceback``.
 37API functions exist to interact with the error indicator in various ways.  There
 38is a separate error indicator for each thread.
 39
 40.. XXX Order of these should be more thoughtful.
 41   Either alphabetical or some kind of structure.
 42
 43
 44.. cfunction:: void PyErr_PrintEx(int set_sys_last_vars)
 45
 46   Print a standard traceback to ``sys.stderr`` and clear the error indicator.
 47   Call this function only when the error indicator is set.  (Otherwise it will
 48   cause a fatal error!)
 49
 50   If *set_sys_last_vars* is nonzero, the variables :data:`sys.last_type`,
 51   :data:`sys.last_value` and :data:`sys.last_traceback` will be set to the
 52   type, value and traceback of the printed exception, respectively.
 53
 54
 55.. cfunction:: void PyErr_Print()
 56
 57   Alias for ``PyErr_PrintEx(1)``.
 58
 59
 60.. cfunction:: PyObject* PyErr_Occurred()
 61
 62   Test whether the error indicator is set.  If set, return the exception *type*
 63   (the first argument to the last call to one of the :cfunc:`PyErr_Set\*`
 64   functions or to :cfunc:`PyErr_Restore`).  If not set, return *NULL*.  You do not
 65   own a reference to the return value, so you do not need to :cfunc:`Py_DECREF`
 66   it.
 67
 68   .. note::
 69
 70      Do not compare the return value to a specific exception; use
 71      :cfunc:`PyErr_ExceptionMatches` instead, shown below.  (The comparison could
 72      easily fail since the exception may be an instance instead of a class, in the
 73      case of a class exception, or it may the a subclass of the expected exception.)
 74
 75
 76.. cfunction:: int PyErr_ExceptionMatches(PyObject *exc)
 77
 78   Equivalent to ``PyErr_GivenExceptionMatches(PyErr_Occurred(), exc)``.  This
 79   should only be called when an exception is actually set; a memory access
 80   violation will occur if no exception has been raised.
 81
 82
 83.. cfunction:: int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)
 84
 85   Return true if the *given* exception matches the exception in *exc*.  If
 86   *exc* is a class object, this also returns true when *given* is an instance
 87   of a subclass.  If *exc* is a tuple, all exceptions in the tuple (and
 88   recursively in subtuples) are searched for a match.
 89
 90
 91.. cfunction:: void PyErr_NormalizeException(PyObject**exc, PyObject**val, PyObject**tb)
 92
 93   Under certain circumstances, the values returned by :cfunc:`PyErr_Fetch` below
 94   can be "unnormalized", meaning that ``*exc`` is a class object but ``*val`` is
 95   not an instance of the  same class.  This function can be used to instantiate
 96   the class in that case.  If the values are already normalized, nothing happens.
 97   The delayed normalization is implemented to improve performance.
 98
 99
100.. cfunction:: void PyErr_Clear()
101
102   Clear the error indicator.  If the error indicator is not set, there is no
103   effect.
104
105
106.. cfunction:: void PyErr_Fetch(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
107
108   Retrieve the error indicator into three variables whose addresses are passed.
109   If the error indicator is not set, set all three variables to *NULL*.  If it is
110   set, it will be cleared and you own a reference to each object retrieved.  The
111   value and traceback object may be *NULL* even when the type object is not.
112
113   .. note::
114
115      This function is normally only used by code that needs to handle exceptions or
116      by code that needs to save and restore the error indicator temporarily.
117
118
119.. cfunction:: void PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
120
121   Set  the error indicator from the three objects.  If the error indicator is
122   already set, it is cleared first.  If the objects are *NULL*, the error
123   indicator is cleared.  Do not pass a *NULL* type and non-*NULL* value or
124   traceback.  The exception type should be a class.  Do not pass an invalid
125   exception type or value. (Violating these rules will cause subtle problems
126   later.)  This call takes away a reference to each object: you must own a
127   reference to each object before the call and after the call you no longer own
128   these references.  (If you don't understand this, don't use this function.  I
129   warned you.)
130
131   .. note::
132
133      This function is normally only used by code that needs to save and restore the
134      error indicator temporarily; use :cfunc:`PyErr_Fetch` to save the current
135      exception state.
136
137
138.. cfunction:: void PyErr_SetString(PyObject *type, const char *message)
139
140   This is the most common way to set the error indicator.  The first argument
141   specifies the exception type; it is normally one of the standard exceptions,
142   e.g. :cdata:`PyExc_RuntimeError`.  You need not increment its reference count.
143   The second argument is an error message; it is converted to a string object.
144
145
146.. cfunction:: void PyErr_SetObject(PyObject *type, PyObject *value)
147
148   This function is similar to :cfunc:`PyErr_SetString` but lets you specify an
149   arbitrary Python object for the "value" of the exception.
150
151
152.. cfunction:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)
153
154   This function sets the error indicator and returns *NULL*. *exception* should be
155   a Python exception (class, not an instance).  *format* should be a string,
156   containing format codes, similar to :cfunc:`printf`. The ``width.precision``
157   before a format code is parsed, but the width part is ignored.
158
159   .. % This should be exactly the same as the table in PyString_FromFormat.
160   .. % One should just refer to the other.
161   .. % The descriptions for %zd and %zu are wrong, but the truth is complicated
162   .. % because not all compilers support the %z width modifier -- we fake it
163   .. % when necessary via interpolating PY_FORMAT_SIZE_T.
164   .. % %u, %lu, %zu should have "new in Python 2.5" blurbs.
165
166   +-------------------+---------------+--------------------------------+
167   | Format Characters | Type          | Comment                        |
168   +===================+===============+================================+
169   | :attr:`%%`        | *n/a*         | The literal % character.       |
170   +-------------------+---------------+--------------------------------+
171   | :attr:`%c`        | int           | A single character,            |
172   |                   |               | represented as an C int.       |
173   +-------------------+---------------+--------------------------------+
174   | :attr:`%d`        | int           | Exactly equivalent to          |
175   |                   |               | ``printf("%d")``.              |
176   +-------------------+---------------+--------------------------------+
177   | :attr:`%u`        | unsigned int  | Exactly equivalent to          |
178   |                   |               | ``printf("%u")``.              |
179   +-------------------+---------------+--------------------------------+
180   | :attr:`%ld`       | long          | Exactly equivalent to          |
181   |                   |               | ``printf("%ld")``.             |
182   +-------------------+---------------+--------------------------------+
183   | :attr:`%lu`       | unsigned long | Exactly equivalent to          |
184   |                   |               | ``printf("%lu")``.             |
185   +-------------------+---------------+--------------------------------+
186   | :attr:`%zd`       | Py_ssize_t    | Exactly equivalent to          |
187   |                   |               | ``printf("%zd")``.             |
188   +-------------------+---------------+--------------------------------+
189   | :attr:`%zu`       | size_t        | Exactly equivalent to          |
190   |                   |               | ``printf("%zu")``.             |
191   +-------------------+---------------+--------------------------------+
192   | :attr:`%i`        | int           | Exactly equivalent to          |
193   |                   |               | ``printf("%i")``.              |
194   +-------------------+---------------+--------------------------------+
195   | :attr:`%x`        | int           | Exactly equivalent to          |
196   |                   |               | ``printf("%x")``.              |
197   +-------------------+---------------+--------------------------------+
198   | :attr:`%s`        | char\*        | A null-terminated C character  |
199   |                   |               | array.                         |
200   +-------------------+---------------+--------------------------------+
201   | :attr:`%p`        | void\*        | The hex representation of a C  |
202   |                   |               | pointer. Mostly equivalent to  |
203   |                   |               | ``printf("%p")`` except that   |
204   |                   |               | it is guaranteed to start with |
205   |                   |               | the literal ``0x`` regardless  |
206   |                   |               | of what the platform's         |
207   |                   |               | ``printf`` yields.             |
208   +-------------------+---------------+--------------------------------+
209
210   An unrecognized format character causes all the rest of the format string to be
211   copied as-is to the result string, and any extra arguments discarded.
212
213
214.. cfunction:: void PyErr_SetNone(PyObject *type)
215
216   This is a shorthand for ``PyErr_SetObject(type, Py_None)``.
217
218
219.. cfunction:: int PyErr_BadArgument()
220
221   This is a shorthand for ``PyErr_SetString(PyExc_TypeError, message)``, where
222   *message* indicates that a built-in operation was invoked with an illegal
223   argument.  It is mostly for internal use.
224
225
226.. cfunction:: PyObject* PyErr_NoMemory()
227
228   This is a shorthand for ``PyErr_SetNone(PyExc_MemoryError)``; it returns *NULL*
229   so an object allocation function can write ``return PyErr_NoMemory();`` when it
230   runs out of memory.
231
232
233.. cfunction:: PyObject* PyErr_SetFromErrno(PyObject *type)
234
235   .. index:: single: strerror()
236
237   This is a convenience function to raise an exception when a C library function
238   has returned an error and set the C variable :cdata:`errno`.  It constructs a
239   tuple object whose first item is the integer :cdata:`errno` value and whose
240   second item is the corresponding error message (gotten from :cfunc:`strerror`),
241   and then calls ``PyErr_SetObject(type, object)``.  On Unix, when the
242   :cdata:`errno` value is :const:`EINTR`, indicating an interrupted system call,
243   this calls :cfunc:`PyErr_CheckSignals`, and if that set the error indicator,
244   leaves it set to that.  The function always returns *NULL*, so a wrapper
245   function around a system call can write ``return PyErr_SetFromErrno(type);``
246   when the system call returns an error.
247
248
249.. cfunction:: PyObject* PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)
250
251   Similar to :cfunc:`PyErr_SetFromErrno`, with the additional behavior that if
252   *filename* is not *NULL*, it is passed to the constructor of *type* as a third
253   parameter.  In the case of exceptions such as :exc:`IOError` and :exc:`OSError`,
254   this is used to define the :attr:`filename` attribute of the exception instance.
255
256
257.. cfunction:: PyObject* PyErr_SetFromWindowsErr(int ierr)
258
259   This is a convenience function to raise :exc:`WindowsError`. If called with
260   *ierr* of :cdata:`0`, the error code returned by a call to :cfunc:`GetLastError`
261   is used instead.  It calls the Win32 function :cfunc:`FormatMessage` to retrieve
262   the Windows description of error code given by *ierr* or :cfunc:`GetLastError`,
263   then it constructs a tuple object whose first item is the *ierr* value and whose
264   second item is the corresponding error message (gotten from
265   :cfunc:`FormatMessage`), and then calls ``PyErr_SetObject(PyExc_WindowsError,
266   object)``. This function always returns *NULL*. Availability: Windows.
267
268
269.. cfunction:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)
270
271   Similar to :cfunc:`PyErr_SetFromWindowsErr`, with an additional parameter
272   specifying the exception type to be raised. Availability: Windows.
273
274   .. versionadded:: 2.3
275
276
277.. cfunction:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)
278
279   Similar to :cfunc:`PyErr_SetFromWindowsErr`, with the additional behavior that
280   if *filename* is not *NULL*, it is passed to the constructor of
281   :exc:`WindowsError` as a third parameter. Availability: Windows.
282
283
284.. cfunction:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, char *filename)
285
286   Similar to :cfunc:`PyErr_SetFromWindowsErrWithFilename`, with an additional
287   parameter specifying the exception type to be raised. Availability: Windows.
288
289   .. versionadded:: 2.3
290
291
292.. cfunction:: void PyErr_BadInternalCall()
293
294   This is a shorthand for ``PyErr_SetString(PyExc_TypeError, message)``, where
295   *message* indicates that an internal operation (e.g. a Python/C API function)
296   was invoked with an illegal argument.  It is mostly for internal use.
297
298
299.. cfunction:: int PyErr_WarnEx(PyObject *category, char *message, int stacklevel)
300
301   Issue a warning message.  The *category* argument is a warning category (see
302   below) or *NULL*; the *message* argument is a message string.  *stacklevel* is a
303   positive number giving a number of stack frames; the warning will be issued from
304   the  currently executing line of code in that stack frame.  A *stacklevel* of 1
305   is the function calling :cfunc:`PyErr_WarnEx`, 2 is  the function above that,
306   and so forth.
307
308   This function normally prints a warning message to *sys.stderr*; however, it is
309   also possible that the user has specified that warnings are to be turned into
310   errors, and in that case this will raise an exception.  It is also possible that
311   the function raises an exception because of a problem with the warning machinery
312   (the implementation imports the :mod:`warnings` module to do the heavy lifting).
313   The return value is ``0`` if no exception is raised, or ``-1`` if an exception
314   is raised.  (It is not possible to determine whether a warning message is
315   actually printed, nor what the reason is for the exception; this is
316   intentional.)  If an exception is raised, the caller should do its normal
317   exception handling (for example, :cfunc:`Py_DECREF` owned references and return
318   an error value).
319
320   Warning categories must be subclasses of :cdata:`Warning`; the default warning
321   category is :cdata:`RuntimeWarning`.  The standard Python warning categories are
322   available as global variables whose names are ``PyExc_`` followed by the Python
323   exception name. These have the type :ctype:`PyObject\*`; they are all class
324   objects. Their names are :cdata:`PyExc_Warning`, :cdata:`PyExc_UserWarning`,
325   :cdata:`PyExc_UnicodeWarning`, :cdata:`PyExc_DeprecationWarning`,
326   :cdata:`PyExc_SyntaxWarning`, :cdata:`PyExc_RuntimeWarning`, and
327   :cdata:`PyExc_FutureWarning`.  :cdata:`PyExc_Warning` is a subclass of
328   :cdata:`PyExc_Exception`; the other warning categories are subclasses of
329   :cdata:`PyExc_Warning`.
330
331   For information about warning control, see the documentation for the
332   :mod:`warnings` module and the :option:`-W` option in the command line
333   documentation.  There is no C API for warning control.
334
335
336.. cfunction:: int PyErr_Warn(PyObject *category, char *message)
337
338   Issue a warning message.  The *category* argument is a warning category (see
339   below) or *NULL*; the *message* argument is a message string.  The warning will
340   appear to be issued from the function calling :cfunc:`PyErr_Warn`, equivalent to
341   calling :cfunc:`PyErr_WarnEx` with a *stacklevel* of 1.
342
343   Deprecated; use :cfunc:`PyErr_WarnEx` instead.
344
345
346.. cfunction:: int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)
347
348   Issue a warning message with explicit control over all warning attributes.  This
349   is a straightforward wrapper around the Python function
350   :func:`warnings.warn_explicit`, see there for more information.  The *module*
351   and *registry* arguments may be set to *NULL* to get the default effect
352   described there.
353
354
355.. cfunction:: int PyErr_WarnPy3k(char *message, int stacklevel)
356
357   Issue a :exc:`DeprecationWarning` with the given *message* and *stacklevel*
358   if the :cdata:`Py_Py3kWarningFlag` flag is enabled.
359
360   .. versionadded:: 2.6
361
362
363.. cfunction:: int PyErr_CheckSignals()
364
365   .. index::
366      module: signal
367      single: SIGINT
368      single: KeyboardInterrupt (built-in exception)
369
370   This function interacts with Python's signal handling.  It checks whether a
371   signal has been sent to the processes and if so, invokes the corresponding
372   signal handler.  If the :mod:`signal` module is supported, this can invoke a
373   signal handler written in Python.  In all cases, the default effect for
374   :const:`SIGINT` is to raise the  :exc:`KeyboardInterrupt` exception.  If an
375   exception is raised the error indicator is set and the function returns ``-1``;
376   otherwise the function returns ``0``.  The error indicator may or may not be
377   cleared if it was previously set.
378
379
380.. cfunction:: void PyErr_SetInterrupt()
381
382   .. index::
383      single: SIGINT
384      single: KeyboardInterrupt (built-in exception)
385
386   This function simulates the effect of a :const:`SIGINT` signal arriving --- the
387   next time :cfunc:`PyErr_CheckSignals` is called,  :exc:`KeyboardInterrupt` will
388   be raised.  It may be called without holding the interpreter lock.
389
390   .. % XXX This was described as obsolete, but is used in
391   .. % thread.interrupt_main() (used from IDLE), so it's still needed.
392
393
394.. cfunction:: int PySignal_SetWakeupFd(int fd)
395
396   This utility function specifies a file descriptor to which a ``'\0'`` byte will
397   be written whenever a signal is received.  It returns the previous such file
398   descriptor.  The value ``-1`` disables the feature; this is the initial state.
399   This is equivalent to :func:`signal.set_wakeup_fd` in Python, but without any
400   error checking.  *fd* should be a valid file descriptor.  The function should
401   only be called from the main thread.
402
403
404.. cfunction:: PyObject* PyErr_NewException(char *name, PyObject *base, PyObject *dict)
405
406   This utility function creates and returns a new exception object. The *name*
407   argument must be the name of the new exception, a C string of the form
408   ``module.class``.  The *base* and *dict* arguments are normally *NULL*.  This
409   creates a class object derived from :exc:`Exception` (accessible in C as
410   :cdata:`PyExc_Exception`).
411
412   The :attr:`__module__` attribute of the new class is set to the first part (up
413   to the last dot) of the *name* argument, and the class name is set to the last
414   part (after the last dot).  The *base* argument can be used to specify alternate
415   base classes; it can either be only one class or a tuple of classes. The *dict*
416   argument can be used to specify a dictionary of class variables and methods.
417
418
419.. cfunction:: void PyErr_WriteUnraisable(PyObject *obj)
420
421   This utility function prints a warning message to ``sys.stderr`` when an
422   exception has been set but it is impossible for the interpreter to actually
423   raise the exception.  It is used, for example, when an exception occurs in an
424   :meth:`__del__` method.
425
426   The function is called with a single argument *obj* that identifies the context
427   in which the unraisable exception occurred. The repr of *obj* will be printed in
428   the warning message.
429
430
431.. _standardexceptions:
432
433Standard Exceptions
434===================
435
436All standard Python exceptions are available as global variables whose names are
437``PyExc_`` followed by the Python exception name.  These have the type
438:ctype:`PyObject\*`; they are all class objects.  For completeness, here are all
439the variables:
440
441+------------------------------------+----------------------------+----------+
442| C Name                             | Python Name                | Notes    |
443+====================================+============================+==========+
444| :cdata:`PyExc_BaseException`       | :exc:`BaseException`       | (1), (4) |
445+------------------------------------+----------------------------+----------+
446| :cdata:`PyExc_Exception`           | :exc:`Exception`           | \(1)     |
447+------------------------------------+----------------------------+----------+
448| :cdata:`PyExc_StandardError`       | :exc:`StandardError`       | \(1)     |
449+------------------------------------+----------------------------+----------+
450| :cdata:`PyExc_ArithmeticError`     | :exc:`ArithmeticError`     | \(1)     |
451+------------------------------------+----------------------------+----------+
452| :cdata:`PyExc_LookupError`         | :exc:`LookupError`         | \(1)     |
453+------------------------------------+----------------------------+----------+
454| :cdata:`PyExc_AssertionError`      | :exc:`AssertionError`      |          |
455+------------------------------------+----------------------------+----------+
456| :cdata:`PyExc_AttributeError`      | :exc:`AttributeError`      |          |
457+------------------------------------+----------------------------+----------+
458| :cdata:`PyExc_EOFError`            | :exc:`EOFError`            |          |
459+------------------------------------+----------------------------+----------+
460| :cdata:`PyExc_EnvironmentError`    | :exc:`EnvironmentError`    | \(1)     |
461+------------------------------------+----------------------------+----------+
462| :cdata:`PyExc_FloatingPointError`  | :exc:`FloatingPointError`  |          |
463+------------------------------------+----------------------------+----------+
464| :cdata:`PyExc_IOError`             | :exc:`IOError`             |          |
465+------------------------------------+----------------------------+----------+
466| :cdata:`PyExc_ImportError`         | :exc:`ImportError`         |          |
467+------------------------------------+----------------------------+----------+
468| :cdata:`PyExc_IndexError`          | :exc:`IndexError`          |          |
469+------------------------------------+----------------------------+----------+
470| :cdata:`PyExc_KeyError`            | :exc:`KeyError`            |          |
471+------------------------------------+----------------------------+----------+
472| :cdata:`PyExc_KeyboardInterrupt`   | :exc:`KeyboardInterrupt`   |          |
473+------------------------------------+----------------------------+----------+
474| :cdata:`PyExc_MemoryError`         | :exc:`MemoryError`         |          |
475+------------------------------------+----------------------------+----------+
476| :cdata:`PyExc_NameError`           | :exc:`NameError`           |          |
477+------------------------------------+----------------------------+----------+
478| :cdata:`PyExc_NotImplementedError` | :exc:`NotImplementedError` |          |
479+------------------------------------+----------------------------+----------+
480| :cdata:`PyExc_OSError`             | :exc:`OSError`             |          |
481+------------------------------------+----------------------------+----------+
482| :cdata:`PyExc_OverflowError`       | :exc:`OverflowError`       |          |
483+------------------------------------+----------------------------+----------+
484| :cdata:`PyExc_ReferenceError`      | :exc:`ReferenceError`      | \(2)     |
485+------------------------------------+----------------------------+----------+
486| :cdata:`PyExc_RuntimeError`        | :exc:`RuntimeError`        |          |
487+------------------------------------+----------------------------+----------+
488| :cdata:`PyExc_SyntaxError`         | :exc:`SyntaxError`         |          |
489+------------------------------------+----------------------------+----------+
490| :cdata:`PyExc_SystemError`         | :exc:`SystemError`         |          |
491+------------------------------------+----------------------------+----------+
492| :cdata:`PyExc_SystemExit`          | :exc:`SystemExit`          |          |
493+------------------------------------+----------------------------+----------+
494| :cdata:`PyExc_TypeError`           | :exc:`TypeError`           |          |
495+------------------------------------+----------------------------+----------+
496| :cdata:`PyExc_ValueError`          | :exc:`ValueError`          |          |
497+------------------------------------+----------------------------+----------+
498| :cdata:`PyExc_WindowsError`        | :exc:`WindowsError`        | \(3)     |
499+------------------------------------+----------------------------+----------+
500| :cdata:`PyExc_ZeroDivisionError`   | :exc:`ZeroDivisionError`   |          |
501+------------------------------------+----------------------------+----------+
502
503.. index::
504   single: PyExc_BaseException
505   single: PyExc_Exception
506   single: PyExc_StandardError
507   single: PyExc_ArithmeticError
508   single: PyExc_LookupError
509   single: PyExc_AssertionError
510   single: PyExc_AttributeError
511   single: PyExc_EOFError
512   single: PyExc_EnvironmentError
513   single: PyExc_FloatingPointError
514   single: PyExc_IOError
515   single: PyExc_ImportError
516   single: PyExc_IndexError
517   single: PyExc_KeyError
518   single: PyExc_KeyboardInterrupt
519   single: PyExc_MemoryError
520   single: PyExc_NameError
521   single: PyExc_NotImplementedError
522   single: PyExc_OSError
523   single: PyExc_OverflowError
524   single: PyExc_ReferenceError
525   single: PyExc_RuntimeError
526   single: PyExc_SyntaxError
527   single: PyExc_SystemError
528   single: PyExc_SystemExit
529   single: PyExc_TypeError
530   single: PyExc_ValueError
531   single: PyExc_WindowsError
532   single: PyExc_ZeroDivisionError
533
534Notes:
535
536(1)
537   This is a base class for other standard exceptions.
538
539(2)
540   This is the same as :exc:`weakref.ReferenceError`.
541
542(3)
543   Only defined on Windows; protect code that uses this by testing that the
544   preprocessor macro ``MS_WINDOWS`` is defined.
545
546(4)
547   .. versionadded:: 2.5
548
549
550Deprecation of String Exceptions
551================================
552
553.. index:: single: BaseException (built-in exception)
554
555All exceptions built into Python or provided in the standard library are derived
556from :exc:`BaseException`.
557
558String exceptions are still supported in the interpreter to allow existing code
559to run unmodified, but this will also change in a future release.
560