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
|
\section{Built-in Exceptions}
\declaremodule{standard}{exceptions}
\modulesynopsis{Standard exception classes.}
Exceptions should be class objects.
The exceptions are defined in the module \module{exceptions}. This
module never needs to be imported explicitly: the exceptions are
provided in the built-in namespace as well as the \module{exceptions}
module.
For class exceptions, in a \keyword{try}\stindex{try} statement with
an \keyword{except}\stindex{except} clause that mentions a particular
class, that clause also handles any exception classes derived from
that class (but not exception classes from which \emph{it} is
derived). Two exception classes that are not related via subclassing
are never equivalent, even if they have the same name.
The built-in exceptions listed below can be generated by the
interpreter or built-in functions. Except where mentioned, they have
an ``associated value'' indicating the detailed cause of the error.
This may be a string or a tuple containing several items of
information (e.g., an error code and a string explaining the code).
The associated value is the second argument to the
\keyword{raise}\stindex{raise} statement. If the exception class is
derived from the standard root class \exception{BaseException}, the
associated value is present as the exception instance's \member{args}
attribute.
User code can raise built-in exceptions. This can be used to test an
exception handler or to report an error condition ``just like'' the
situation in which the interpreter raises the same exception; but
beware that there is nothing to prevent user code from raising an
inappropriate error.
The built-in exception classes can be sub-classed to define new
exceptions; programmers are encouraged to at least derive new
exceptions from the \exception{Exception} class and not
\exception{BaseException}. More
information on defining exceptions is available in the
\citetitle[../tut/tut.html]{Python Tutorial} under the heading
``User-defined Exceptions.''
\setindexsubitem{(built-in exception base class)}
The following exceptions are only used as base classes for other
exceptions.
\begin{excdesc}{BaseException}
The base class for all built-in exceptions. It is not meant to be directly
inherited by user-defined classes (for that use \exception{Exception}). If
\function{str()} or \function{unicode()} is called on an instance of this
class, the representation of the argument(s) to the instance are returned or
the emptry string when there were no arguments. All arguments are
stored in \member{args} as a tuple.
\versionadded{2.5}
\end{excdesc}
\begin{excdesc}{Exception}
All built-in, non-system-exiting exceptions are derived
from this class. All user-defined exceptions should also be derived
from this class.
\versionchanged[Changed to inherit from \exception{BaseException}]{2.5}
\end{excdesc}
\begin{excdesc}{ArithmeticError}
The base class for those built-in exceptions that are raised for
various arithmetic errors: \exception{OverflowError},
\exception{ZeroDivisionError}, \exception{FloatingPointError}.
\end{excdesc}
\begin{excdesc}{LookupError}
The base class for the exceptions that are raised when a key or
index used on a mapping or sequence is invalid: \exception{IndexError},
\exception{KeyError}. This can be raised directly by
\function{sys.setdefaultencoding()}.
\end{excdesc}
\begin{excdesc}{EnvironmentError}
The base class for exceptions that
can occur outside the Python system: \exception{IOError},
\exception{OSError}. When exceptions of this type are created with a
2-tuple, the first item is available on the instance's \member{errno}
attribute (it is assumed to be an error number), and the second item
is available on the \member{strerror} attribute (it is usually the
associated error message). The tuple itself is also available on the
\member{args} attribute.
\versionadded{1.5.2}
When an \exception{EnvironmentError} exception is instantiated with a
3-tuple, the first two items are available as above, while the third
item is available on the \member{filename} attribute. However, for
backwards compatibility, the \member{args} attribute contains only a
2-tuple of the first two constructor arguments.
The \member{filename} attribute is \code{None} when this exception is
created with other than 3 arguments. The \member{errno} and
\member{strerror} attributes are also \code{None} when the instance was
created with other than 2 or 3 arguments. In this last case,
\member{args} contains the verbatim constructor arguments as a tuple.
\end{excdesc}
\setindexsubitem{(built-in exception)}
The following exceptions are the exceptions that are actually raised.
\begin{excdesc}{AssertionError}
\stindex{assert}
Raised when an \keyword{assert} statement fails.
\end{excdesc}
\begin{excdesc}{AttributeError}
% xref to attribute reference?
Raised when an attribute reference or assignment fails. (When an
object does not support attribute references or attribute assignments
at all, \exception{TypeError} is raised.)
\end{excdesc}
\begin{excdesc}{EOFError}
% XXXJH xrefs here
Raised when attempting to read beyond the end of a file.
% XXXJH xrefs here
(N.B.: the \method{read()} and \method{readline()} methods of file
objects return an empty string when they hit \EOF.)
\end{excdesc}
\begin{excdesc}{FloatingPointError}
Raised when a floating point operation fails. This exception is
always defined, but can only be raised when Python is configured
with the \longprogramopt{with-fpectl} option, or the
\constant{WANT_SIGFPE_HANDLER} symbol is defined in the
\file{pyconfig.h} file.
\end{excdesc}
\begin{excdesc}{GeneratorExit}
Raise when a generator's \method{close()} method is called.
\versionadded{2.5}
\versionchanged[Changed to inherit from Exception instead of
StandardError]{3.0}
\end{excdesc}
\begin{excdesc}{IOError}
% XXXJH xrefs here
Raised when an I/O operation (such as a \keyword{print} statement,
the built-in \function{open()} function or a method of a file
object) fails for an I/O-related reason, e.g., ``file not found'' or
``disk full''.
This class is derived from \exception{EnvironmentError}. See the
discussion above for more information on exception instance
attributes.
\end{excdesc}
\begin{excdesc}{ImportError}
% XXXJH xref to import statement?
Raised when an \keyword{import} statement fails to find the module
definition or when a \code{from \textrm{\ldots} import} fails to find a
name that is to be imported.
\end{excdesc}
\begin{excdesc}{IndexError}
% XXXJH xref to sequences
Raised when a sequence subscript is out of range. (Slice indices are
silently truncated to fall in the allowed range; if an index is not a
plain integer, \exception{TypeError} is raised.)
\end{excdesc}
\begin{excdesc}{KeyError}
% XXXJH xref to mapping objects?
Raised when a mapping (dictionary) key is not found in the set of
existing keys.
\end{excdesc}
\begin{excdesc}{KeyboardInterrupt}
Raised when the user hits the interrupt key (normally
\kbd{Control-C} or \kbd{Delete}). During execution, a check for
interrupts is made regularly.
% XXX(hylton) xrefs here
The exception inherits from \exception{BaseException} so as to not be
accidentally caught by code that catches \exception{Exception} and thus
prevent the interpreter from exiting.
\versionchanged[Changed to inherit from \exception{BaseException}]{2.5}
\end{excdesc}
\begin{excdesc}{MemoryError}
Raised when an operation runs out of memory but the situation may
still be rescued (by deleting some objects). The associated value is
a string indicating what kind of (internal) operation ran out of memory.
Note that because of the underlying memory management architecture
(C's \cfunction{malloc()} function), the interpreter may not
always be able to completely recover from this situation; it
nevertheless raises an exception so that a stack traceback can be
printed, in case a run-away program was the cause.
\end{excdesc}
\begin{excdesc}{NameError}
Raised when a local or global name is not found. This applies only
to unqualified names. The associated value is an error message that
includes the name that could not be found.
\end{excdesc}
\begin{excdesc}{NotImplementedError}
This exception is derived from \exception{RuntimeError}. In user
defined base classes, abstract methods should raise this exception
when they require derived classes to override the method.
\versionadded{1.5.2}
\end{excdesc}
\begin{excdesc}{OSError}
%xref for os module
This class is derived from \exception{EnvironmentError} and is used
primarily as the \refmodule{os} module's \code{os.error} exception.
See \exception{EnvironmentError} above for a description of the
possible associated values.
\versionadded{1.5.2}
\end{excdesc}
\begin{excdesc}{OverflowError}
% XXXJH reference to long's and/or int's?
Raised when the result of an arithmetic operation is too large to be
represented. This cannot occur for long integers (which would rather
raise \exception{MemoryError} than give up). Because of the lack of
standardization of floating point exception handling in C, most
floating point operations also aren't checked. For plain integers,
all operations that can overflow are checked except left shift, where
typical applications prefer to drop bits than raise an exception.
\end{excdesc}
\begin{excdesc}{ReferenceError}
This exception is raised when a weak reference proxy, created by the
\function{\refmodule{weakref}.proxy()} function, is used to access
an attribute of the referent after it has been garbage collected.
For more information on weak references, see the \refmodule{weakref}
module.
\versionadded[Previously known as the
\exception{\refmodule{weakref}.ReferenceError}
exception]{2.2}
\end{excdesc}
\begin{excdesc}{RuntimeError}
Raised when an error is detected that doesn't fall in any of the
other categories. The associated value is a string indicating what
precisely went wrong. (This exception is mostly a relic from a
previous version of the interpreter; it is not used very much any
more.)
\end{excdesc}
\begin{excdesc}{StopIteration}
Raised by builtin \function{next()} and an iterator's \method{__next__()}
method to signal that there are no further values.
\versionadded{2.2}
\versionchanged[Changed to inherit from Exception instead of
StandardError]{3.0}
\end{excdesc}
\begin{excdesc}{SyntaxError}
% XXXJH xref to these functions?
Raised when the parser encounters a syntax error. This may occur in
an \keyword{import} statement, in a call to the built-in functions
\function{exec()}, \function{execfile()}, \function{eval()} or
\function{input()}, or when reading the initial script or standard
input (also interactively).
Instances of this class have attributes \member{filename},
\member{lineno}, \member{offset} and \member{text} for easier access
to the details. \function{str()} of the exception instance returns
only the message.
\end{excdesc}
\begin{excdesc}{SystemError}
Raised when the interpreter finds an internal error, but the
situation does not look so serious to cause it to abandon all hope.
The associated value is a string indicating what went wrong (in
low-level terms).
You should report this to the author or maintainer of your Python
interpreter. Be sure to report the version of the Python
interpreter (\code{sys.version}; it is also printed at the start of an
interactive Python session), the exact error message (the exception's
associated value) and if possible the source of the program that
triggered the error.
\end{excdesc}
\begin{excdesc}{SystemExit}
% XXX(hylton) xref to module sys?
This exception is raised by the \function{sys.exit()} function. When it
is not handled, the Python interpreter exits; no stack traceback is
printed. If the associated value is a plain integer, it specifies the
system exit status (passed to C's \cfunction{exit()} function); if it is
\code{None}, the exit status is zero; if it has another type (such as
a string), the object's value is printed and the exit status is one.
Instances have an attribute \member{code} which is set to the
proposed exit status or error message (defaulting to \code{None}).
Also, this exception derives directly from \exception{BaseException} and
not \exception{Exception}, since it is not technically an error.
A call to \function{sys.exit()} is translated into an exception so that
clean-up handlers (\keyword{finally} clauses of \keyword{try} statements)
can be executed, and so that a debugger can execute a script without
running the risk of losing control. The \function{os._exit()} function
can be used if it is absolutely positively necessary to exit
immediately (for example, in the child process after a call to
\function{fork()}).
The exception inherits from \exception{BaseException} instead of
\exception{Exception} so that it is not
accidentally caught by code that catches \exception{Exception}. This allows
the exception to properly propagate up and cause the interpreter to exit.
\versionchanged[Changed to inherit from \exception{BaseException}]{2.5}
\end{excdesc}
\begin{excdesc}{TypeError}
Raised when an operation or function is applied to an object
of inappropriate type. The associated value is a string giving
details about the type mismatch.
\end{excdesc}
\begin{excdesc}{UnboundLocalError}
Raised when a reference is made to a local variable in a function or
method, but no value has been bound to that variable. This is a
subclass of \exception{NameError}.
\versionadded{2.0}
\end{excdesc}
\begin{excdesc}{UnicodeError}
Raised when a Unicode-related encoding or decoding error occurs. It
is a subclass of \exception{ValueError}.
\versionadded{2.0}
\end{excdesc}
\begin{excdesc}{UnicodeEncodeError}
Raised when a Unicode-related error occurs during encoding. It
is a subclass of \exception{UnicodeError}.
\versionadded{2.3}
\end{excdesc}
\begin{excdesc}{UnicodeDecodeError}
Raised when a Unicode-related error occurs during decoding. It
is a subclass of \exception{UnicodeError}.
\versionadded{2.3}
\end{excdesc}
\begin{excdesc}{UnicodeTranslateError}
Raised when a Unicode-related error occurs during translating. It
is a subclass of \exception{UnicodeError}.
\versionadded{2.3}
\end{excdesc}
\begin{excdesc}{ValueError}
Raised when a built-in operation or function receives an argument
that has the right type but an inappropriate value, and the
situation is not described by a more precise exception such as
\exception{IndexError}.
\end{excdesc}
\begin{excdesc}{WindowsError}
Raised when a Windows-specific error occurs or when the error number
does not correspond to an \cdata{errno} value. The
\member{winerror} and \member{strerror} values are created from the
return values of the \cfunction{GetLastError()} and
\cfunction{FormatMessage()} functions from the Windows Platform API.
The \member{errno} value maps the \member{winerror} value to
corresponding \code{errno.h} values.
This is a subclass of \exception{OSError}.
\versionadded{2.0}
\versionchanged[Previous versions put the \cfunction{GetLastError()}
codes into \member{errno}]{2.5}
\end{excdesc}
\begin{excdesc}{ZeroDivisionError}
Raised when the second argument of a division or modulo operation is
zero. The associated value is a string indicating the type of the
operands and the operation.
\end{excdesc}
\setindexsubitem{(built-in warning)}
The following exceptions are used as warning categories; see the
\refmodule{warnings} module for more information.
\begin{excdesc}{Warning}
Base class for warning categories.
\end{excdesc}
\begin{excdesc}{UserWarning}
Base class for warnings generated by user code.
\end{excdesc}
\begin{excdesc}{DeprecationWarning}
Base class for warnings about deprecated features.
\end{excdesc}
\begin{excdesc}{PendingDeprecationWarning}
Base class for warnings about features which will be deprecated in the future.
\end{excdesc}
\begin{excdesc}{SyntaxWarning}
Base class for warnings about dubious syntax
\end{excdesc}
\begin{excdesc}{RuntimeWarning}
Base class for warnings about dubious runtime behavior.
\end{excdesc}
\begin{excdesc}{FutureWarning}
Base class for warnings about constructs that will change semantically
in the future.
\end{excdesc}
\begin{excdesc}{ImportWarning}
Base class for warnings about probable mistakes in module imports.
\versionadded{2.5}
\end{excdesc}
\begin{excdesc}{UnicodeWarning}
Base class for warnings related to Unicode.
\versionadded{2.5}
\end{excdesc}
The class hierarchy for built-in exceptions is:
\verbatiminput{../../Lib/test/exception_hierarchy.txt}
|