10 The functions described in this chapter will let you handle and raise Python
11 exceptions. It is important to understand some of the basics of Python
12 exception handling. It works somewhat like the Unix :cdata:`errno` variable:
13 there is a global indicator (per thread) of the last error that occurred. Most
14 functions don't clear this on success, but will set it to indicate the cause of
15 the 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
17 integer (exception: the :cfunc:`PyArg_\*` functions return ``1`` for success and
20 When a function must fail because some function it called failed, it generally
21 doesn't set the error indicator; the function it called already set it. It is
22 responsible for either handling the error and clearing the exception or
23 returning after cleaning up any resources it holds (such as object references or
24 memory allocations); it should *not* continue normally if it is not prepared to
25 handle the error. If returning due to an error, it is important to indicate to
26 the caller that an error has been set. If the error is not handled or carefully
27 propagated, additional calls into the Python/C API may not behave as intended
28 and may fail in mysterious ways.
31 single: exc_type (in module sys)
32 single: exc_value (in module sys)
33 single: exc_traceback (in module sys)
35 The error indicator consists of three Python objects corresponding to the
36 Python variables ``sys.exc_type``, ``sys.exc_value`` and ``sys.exc_traceback``.
37 API functions exist to interact with the error indicator in various ways. There
38 is a separate error indicator for each thread.
40 .. XXX Order of these should be more thoughtful.
41 Either alphabetical or some kind of structure.
44 .. cfunction:: void PyErr_PrintEx(int set_sys_last_vars)
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
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.
55 .. cfunction:: void PyErr_Print()
57 Alias for ``PyErr_PrintEx(1)``.
60 .. cfunction:: PyObject* PyErr_Occurred()
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`
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.)
76 .. cfunction:: int PyErr_ExceptionMatches(PyObject *exc)
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.
83 .. cfunction:: int PyErr_GivenExceptionMatches(PyObject *given, PyObject *exc)
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.
91 .. cfunction:: void PyErr_NormalizeException(PyObject**exc, PyObject**val, PyObject**tb)
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.
100 .. cfunction:: void PyErr_Clear()
102 Clear the error indicator. If the error indicator is not set, there is no
106 .. cfunction:: void PyErr_Fetch(PyObject **ptype, PyObject **pvalue, PyObject **ptraceback)
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.
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.
119 .. cfunction:: void PyErr_Restore(PyObject *type, PyObject *value, PyObject *traceback)
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
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
138 .. cfunction:: void PyErr_SetString(PyObject *type, const char *message)
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.
146 .. cfunction:: void PyErr_SetObject(PyObject *type, PyObject *value)
148 This function is similar to :cfunc:`PyErr_SetString` but lets you specify an
149 arbitrary Python object for the "value" of the exception.
152 .. cfunction:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)
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.
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 .. % Similar comments apply to the %ll width modifier and
165 .. % PY_FORMAT_LONG_LONG.
166 .. % %u, %lu, %zu should have "new in Python 2.5" blurbs.
168 +-------------------+---------------+--------------------------------+
169 | Format Characters | Type | Comment |
170 +===================+===============+================================+
171 | :attr:`%%` | *n/a* | The literal % character. |
172 +-------------------+---------------+--------------------------------+
173 | :attr:`%c` | int | A single character, |
174 | | | represented as an C int. |
175 +-------------------+---------------+--------------------------------+
176 | :attr:`%d` | int | Exactly equivalent to |
177 | | | ``printf("%d")``. |
178 +-------------------+---------------+--------------------------------+
179 | :attr:`%u` | unsigned int | Exactly equivalent to |
180 | | | ``printf("%u")``. |
181 +-------------------+---------------+--------------------------------+
182 | :attr:`%ld` | long | Exactly equivalent to |
183 | | | ``printf("%ld")``. |
184 +-------------------+---------------+--------------------------------+
185 | :attr:`%lu` | unsigned long | Exactly equivalent to |
186 | | | ``printf("%lu")``. |
187 +-------------------+---------------+--------------------------------+
188 | :attr:`%lld` | long long | Exactly equivalent to |
189 | | | ``printf("%lld")``. |
190 +-------------------+---------------+--------------------------------+
191 | :attr:`%llu` | unsigned | Exactly equivalent to |
192 | | long long | ``printf("%llu")``. |
193 +-------------------+---------------+--------------------------------+
194 | :attr:`%zd` | Py_ssize_t | Exactly equivalent to |
195 | | | ``printf("%zd")``. |
196 +-------------------+---------------+--------------------------------+
197 | :attr:`%zu` | size_t | Exactly equivalent to |
198 | | | ``printf("%zu")``. |
199 +-------------------+---------------+--------------------------------+
200 | :attr:`%i` | int | Exactly equivalent to |
201 | | | ``printf("%i")``. |
202 +-------------------+---------------+--------------------------------+
203 | :attr:`%x` | int | Exactly equivalent to |
204 | | | ``printf("%x")``. |
205 +-------------------+---------------+--------------------------------+
206 | :attr:`%s` | char\* | A null-terminated C character |
208 +-------------------+---------------+--------------------------------+
209 | :attr:`%p` | void\* | The hex representation of a C |
210 | | | pointer. Mostly equivalent to |
211 | | | ``printf("%p")`` except that |
212 | | | it is guaranteed to start with |
213 | | | the literal ``0x`` regardless |
214 | | | of what the platform's |
215 | | | ``printf`` yields. |
216 +-------------------+---------------+--------------------------------+
218 An unrecognized format character causes all the rest of the format string to be
219 copied as-is to the result string, and any extra arguments discarded.
223 The `"%lld"` and `"%llu"` format specifiers are only available
224 when `HAVE_LONG_LONG` is defined.
226 .. versionchanged:: 2.7
227 Support for `"%lld"` and `"%llu"` added.
230 .. cfunction:: void PyErr_SetNone(PyObject *type)
232 This is a shorthand for ``PyErr_SetObject(type, Py_None)``.
235 .. cfunction:: int PyErr_BadArgument()
237 This is a shorthand for ``PyErr_SetString(PyExc_TypeError, message)``, where
238 *message* indicates that a built-in operation was invoked with an illegal
239 argument. It is mostly for internal use.
242 .. cfunction:: PyObject* PyErr_NoMemory()
244 This is a shorthand for ``PyErr_SetNone(PyExc_MemoryError)``; it returns *NULL*
245 so an object allocation function can write ``return PyErr_NoMemory();`` when it
249 .. cfunction:: PyObject* PyErr_SetFromErrno(PyObject *type)
251 .. index:: single: strerror()
253 This is a convenience function to raise an exception when a C library function
254 has returned an error and set the C variable :cdata:`errno`. It constructs a
255 tuple object whose first item is the integer :cdata:`errno` value and whose
256 second item is the corresponding error message (gotten from :cfunc:`strerror`),
257 and then calls ``PyErr_SetObject(type, object)``. On Unix, when the
258 :cdata:`errno` value is :const:`EINTR`, indicating an interrupted system call,
259 this calls :cfunc:`PyErr_CheckSignals`, and if that set the error indicator,
260 leaves it set to that. The function always returns *NULL*, so a wrapper
261 function around a system call can write ``return PyErr_SetFromErrno(type);``
262 when the system call returns an error.
265 .. cfunction:: PyObject* PyErr_SetFromErrnoWithFilename(PyObject *type, const char *filename)
267 Similar to :cfunc:`PyErr_SetFromErrno`, with the additional behavior that if
268 *filename* is not *NULL*, it is passed to the constructor of *type* as a third
269 parameter. In the case of exceptions such as :exc:`IOError` and :exc:`OSError`,
270 this is used to define the :attr:`filename` attribute of the exception instance.
273 .. cfunction:: PyObject* PyErr_SetFromWindowsErr(int ierr)
275 This is a convenience function to raise :exc:`WindowsError`. If called with
276 *ierr* of :cdata:`0`, the error code returned by a call to :cfunc:`GetLastError`
277 is used instead. It calls the Win32 function :cfunc:`FormatMessage` to retrieve
278 the Windows description of error code given by *ierr* or :cfunc:`GetLastError`,
279 then it constructs a tuple object whose first item is the *ierr* value and whose
280 second item is the corresponding error message (gotten from
281 :cfunc:`FormatMessage`), and then calls ``PyErr_SetObject(PyExc_WindowsError,
282 object)``. This function always returns *NULL*. Availability: Windows.
285 .. cfunction:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)
287 Similar to :cfunc:`PyErr_SetFromWindowsErr`, with an additional parameter
288 specifying the exception type to be raised. Availability: Windows.
290 .. versionadded:: 2.3
293 .. cfunction:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)
295 Similar to :cfunc:`PyErr_SetFromWindowsErr`, with the additional behavior that
296 if *filename* is not *NULL*, it is passed to the constructor of
297 :exc:`WindowsError` as a third parameter. Availability: Windows.
300 .. cfunction:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, char *filename)
302 Similar to :cfunc:`PyErr_SetFromWindowsErrWithFilename`, with an additional
303 parameter specifying the exception type to be raised. Availability: Windows.
305 .. versionadded:: 2.3
308 .. cfunction:: void PyErr_BadInternalCall()
310 This is a shorthand for ``PyErr_SetString(PyExc_SystemError, message)``,
311 where *message* indicates that an internal operation (e.g. a Python/C API
312 function) was invoked with an illegal argument. It is mostly for internal
316 .. cfunction:: int PyErr_WarnEx(PyObject *category, char *message, int stacklevel)
318 Issue a warning message. The *category* argument is a warning category (see
319 below) or *NULL*; the *message* argument is a message string. *stacklevel* is a
320 positive number giving a number of stack frames; the warning will be issued from
321 the currently executing line of code in that stack frame. A *stacklevel* of 1
322 is the function calling :cfunc:`PyErr_WarnEx`, 2 is the function above that,
325 This function normally prints a warning message to *sys.stderr*; however, it is
326 also possible that the user has specified that warnings are to be turned into
327 errors, and in that case this will raise an exception. It is also possible that
328 the function raises an exception because of a problem with the warning machinery
329 (the implementation imports the :mod:`warnings` module to do the heavy lifting).
330 The return value is ``0`` if no exception is raised, or ``-1`` if an exception
331 is raised. (It is not possible to determine whether a warning message is
332 actually printed, nor what the reason is for the exception; this is
333 intentional.) If an exception is raised, the caller should do its normal
334 exception handling (for example, :cfunc:`Py_DECREF` owned references and return
337 Warning categories must be subclasses of :cdata:`Warning`; the default warning
338 category is :cdata:`RuntimeWarning`. The standard Python warning categories are
339 available as global variables whose names are ``PyExc_`` followed by the Python
340 exception name. These have the type :ctype:`PyObject\*`; they are all class
341 objects. Their names are :cdata:`PyExc_Warning`, :cdata:`PyExc_UserWarning`,
342 :cdata:`PyExc_UnicodeWarning`, :cdata:`PyExc_DeprecationWarning`,
343 :cdata:`PyExc_SyntaxWarning`, :cdata:`PyExc_RuntimeWarning`, and
344 :cdata:`PyExc_FutureWarning`. :cdata:`PyExc_Warning` is a subclass of
345 :cdata:`PyExc_Exception`; the other warning categories are subclasses of
346 :cdata:`PyExc_Warning`.
348 For information about warning control, see the documentation for the
349 :mod:`warnings` module and the :option:`-W` option in the command line
350 documentation. There is no C API for warning control.
353 .. cfunction:: int PyErr_Warn(PyObject *category, char *message)
355 Issue a warning message. The *category* argument is a warning category (see
356 below) or *NULL*; the *message* argument is a message string. The warning will
357 appear to be issued from the function calling :cfunc:`PyErr_Warn`, equivalent to
358 calling :cfunc:`PyErr_WarnEx` with a *stacklevel* of 1.
360 Deprecated; use :cfunc:`PyErr_WarnEx` instead.
363 .. cfunction:: int PyErr_WarnExplicit(PyObject *category, const char *message, const char *filename, int lineno, const char *module, PyObject *registry)
365 Issue a warning message with explicit control over all warning attributes. This
366 is a straightforward wrapper around the Python function
367 :func:`warnings.warn_explicit`, see there for more information. The *module*
368 and *registry* arguments may be set to *NULL* to get the default effect
372 .. cfunction:: int PyErr_WarnPy3k(char *message, int stacklevel)
374 Issue a :exc:`DeprecationWarning` with the given *message* and *stacklevel*
375 if the :cdata:`Py_Py3kWarningFlag` flag is enabled.
377 .. versionadded:: 2.6
380 .. cfunction:: int PyErr_CheckSignals()
385 single: KeyboardInterrupt (built-in exception)
387 This function interacts with Python's signal handling. It checks whether a
388 signal has been sent to the processes and if so, invokes the corresponding
389 signal handler. If the :mod:`signal` module is supported, this can invoke a
390 signal handler written in Python. In all cases, the default effect for
391 :const:`SIGINT` is to raise the :exc:`KeyboardInterrupt` exception. If an
392 exception is raised the error indicator is set and the function returns ``-1``;
393 otherwise the function returns ``0``. The error indicator may or may not be
394 cleared if it was previously set.
397 .. cfunction:: void PyErr_SetInterrupt()
401 single: KeyboardInterrupt (built-in exception)
403 This function simulates the effect of a :const:`SIGINT` signal arriving --- the
404 next time :cfunc:`PyErr_CheckSignals` is called, :exc:`KeyboardInterrupt` will
405 be raised. It may be called without holding the interpreter lock.
407 .. % XXX This was described as obsolete, but is used in
408 .. % thread.interrupt_main() (used from IDLE), so it's still needed.
411 .. cfunction:: int PySignal_SetWakeupFd(int fd)
413 This utility function specifies a file descriptor to which a ``'\0'`` byte will
414 be written whenever a signal is received. It returns the previous such file
415 descriptor. The value ``-1`` disables the feature; this is the initial state.
416 This is equivalent to :func:`signal.set_wakeup_fd` in Python, but without any
417 error checking. *fd* should be a valid file descriptor. The function should
418 only be called from the main thread.
421 .. cfunction:: PyObject* PyErr_NewException(char *name, PyObject *base, PyObject *dict)
423 This utility function creates and returns a new exception object. The *name*
424 argument must be the name of the new exception, a C string of the form
425 ``module.class``. The *base* and *dict* arguments are normally *NULL*. This
426 creates a class object derived from :exc:`Exception` (accessible in C as
427 :cdata:`PyExc_Exception`).
429 The :attr:`__module__` attribute of the new class is set to the first part (up
430 to the last dot) of the *name* argument, and the class name is set to the last
431 part (after the last dot). The *base* argument can be used to specify alternate
432 base classes; it can either be only one class or a tuple of classes. The *dict*
433 argument can be used to specify a dictionary of class variables and methods.
436 .. cfunction:: PyObject* PyErr_NewExceptionWithDoc(char *name, char *doc, PyObject *base, PyObject *dict)
438 Same as :cfunc:`PyErr_NewException`, except that the new exception class can
439 easily be given a docstring: If *doc* is non-*NULL*, it will be used as the
440 docstring for the exception class.
442 .. versionadded:: 2.7
445 .. cfunction:: void PyErr_WriteUnraisable(PyObject *obj)
447 This utility function prints a warning message to ``sys.stderr`` when an
448 exception has been set but it is impossible for the interpreter to actually
449 raise the exception. It is used, for example, when an exception occurs in an
450 :meth:`__del__` method.
452 The function is called with a single argument *obj* that identifies the context
453 in which the unraisable exception occurred. The repr of *obj* will be printed in
457 .. _standardexceptions:
462 All standard Python exceptions are available as global variables whose names are
463 ``PyExc_`` followed by the Python exception name. These have the type
464 :ctype:`PyObject\*`; they are all class objects. For completeness, here are all
467 +------------------------------------+----------------------------+----------+
468 | C Name | Python Name | Notes |
469 +====================================+============================+==========+
470 | :cdata:`PyExc_BaseException` | :exc:`BaseException` | (1), (4) |
471 +------------------------------------+----------------------------+----------+
472 | :cdata:`PyExc_Exception` | :exc:`Exception` | \(1) |
473 +------------------------------------+----------------------------+----------+
474 | :cdata:`PyExc_StandardError` | :exc:`StandardError` | \(1) |
475 +------------------------------------+----------------------------+----------+
476 | :cdata:`PyExc_ArithmeticError` | :exc:`ArithmeticError` | \(1) |
477 +------------------------------------+----------------------------+----------+
478 | :cdata:`PyExc_LookupError` | :exc:`LookupError` | \(1) |
479 +------------------------------------+----------------------------+----------+
480 | :cdata:`PyExc_AssertionError` | :exc:`AssertionError` | |
481 +------------------------------------+----------------------------+----------+
482 | :cdata:`PyExc_AttributeError` | :exc:`AttributeError` | |
483 +------------------------------------+----------------------------+----------+
484 | :cdata:`PyExc_EOFError` | :exc:`EOFError` | |
485 +------------------------------------+----------------------------+----------+
486 | :cdata:`PyExc_EnvironmentError` | :exc:`EnvironmentError` | \(1) |
487 +------------------------------------+----------------------------+----------+
488 | :cdata:`PyExc_FloatingPointError` | :exc:`FloatingPointError` | |
489 +------------------------------------+----------------------------+----------+
490 | :cdata:`PyExc_IOError` | :exc:`IOError` | |
491 +------------------------------------+----------------------------+----------+
492 | :cdata:`PyExc_ImportError` | :exc:`ImportError` | |
493 +------------------------------------+----------------------------+----------+
494 | :cdata:`PyExc_IndexError` | :exc:`IndexError` | |
495 +------------------------------------+----------------------------+----------+
496 | :cdata:`PyExc_KeyError` | :exc:`KeyError` | |
497 +------------------------------------+----------------------------+----------+
498 | :cdata:`PyExc_KeyboardInterrupt` | :exc:`KeyboardInterrupt` | |
499 +------------------------------------+----------------------------+----------+
500 | :cdata:`PyExc_MemoryError` | :exc:`MemoryError` | |
501 +------------------------------------+----------------------------+----------+
502 | :cdata:`PyExc_NameError` | :exc:`NameError` | |
503 +------------------------------------+----------------------------+----------+
504 | :cdata:`PyExc_NotImplementedError` | :exc:`NotImplementedError` | |
505 +------------------------------------+----------------------------+----------+
506 | :cdata:`PyExc_OSError` | :exc:`OSError` | |
507 +------------------------------------+----------------------------+----------+
508 | :cdata:`PyExc_OverflowError` | :exc:`OverflowError` | |
509 +------------------------------------+----------------------------+----------+
510 | :cdata:`PyExc_ReferenceError` | :exc:`ReferenceError` | \(2) |
511 +------------------------------------+----------------------------+----------+
512 | :cdata:`PyExc_RuntimeError` | :exc:`RuntimeError` | |
513 +------------------------------------+----------------------------+----------+
514 | :cdata:`PyExc_SyntaxError` | :exc:`SyntaxError` | |
515 +------------------------------------+----------------------------+----------+
516 | :cdata:`PyExc_SystemError` | :exc:`SystemError` | |
517 +------------------------------------+----------------------------+----------+
518 | :cdata:`PyExc_SystemExit` | :exc:`SystemExit` | |
519 +------------------------------------+----------------------------+----------+
520 | :cdata:`PyExc_TypeError` | :exc:`TypeError` | |
521 +------------------------------------+----------------------------+----------+
522 | :cdata:`PyExc_ValueError` | :exc:`ValueError` | |
523 +------------------------------------+----------------------------+----------+
524 | :cdata:`PyExc_WindowsError` | :exc:`WindowsError` | \(3) |
525 +------------------------------------+----------------------------+----------+
526 | :cdata:`PyExc_ZeroDivisionError` | :exc:`ZeroDivisionError` | |
527 +------------------------------------+----------------------------+----------+
530 single: PyExc_BaseException
531 single: PyExc_Exception
532 single: PyExc_StandardError
533 single: PyExc_ArithmeticError
534 single: PyExc_LookupError
535 single: PyExc_AssertionError
536 single: PyExc_AttributeError
537 single: PyExc_EOFError
538 single: PyExc_EnvironmentError
539 single: PyExc_FloatingPointError
540 single: PyExc_IOError
541 single: PyExc_ImportError
542 single: PyExc_IndexError
543 single: PyExc_KeyError
544 single: PyExc_KeyboardInterrupt
545 single: PyExc_MemoryError
546 single: PyExc_NameError
547 single: PyExc_NotImplementedError
548 single: PyExc_OSError
549 single: PyExc_OverflowError
550 single: PyExc_ReferenceError
551 single: PyExc_RuntimeError
552 single: PyExc_SyntaxError
553 single: PyExc_SystemError
554 single: PyExc_SystemExit
555 single: PyExc_TypeError
556 single: PyExc_ValueError
557 single: PyExc_WindowsError
558 single: PyExc_ZeroDivisionError
563 This is a base class for other standard exceptions.
566 This is the same as :exc:`weakref.ReferenceError`.
569 Only defined on Windows; protect code that uses this by testing that the
570 preprocessor macro ``MS_WINDOWS`` is defined.
573 .. versionadded:: 2.5
576 Deprecation of String Exceptions
577 ================================
579 .. index:: single: BaseException (built-in exception)
581 All exceptions built into Python or provided in the standard library are derived
582 from :exc:`BaseException`.
584 String exceptions are still supported in the interpreter to allow existing code
585 to run unmodified, but this will also change in a future release.