/Doc/c-api/exceptions.rst

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