1:mod:`logging` --- Logging facility for Python
2==============================================
3
4.. module:: logging
5   :synopsis: Flexible event logging system for applications.
6
7
8.. moduleauthor:: Vinay Sajip <[email protected]>
9.. sectionauthor:: Vinay Sajip <[email protected]>
10
11
12.. index:: pair: Errors; logging
13
14.. sidebar:: Important
15
16   This page contains the API reference information. For tutorial
17   information and discussion of more advanced topics, see
18
19   * :ref:`Basic Tutorial <logging-basic-tutorial>`
20   * :ref:`Advanced Tutorial <logging-advanced-tutorial>`
21   * :ref:`Logging Cookbook <logging-cookbook>`
22
23**Source code:** :source:`Lib/logging/__init__.py`
24
25--------------
26
27.. versionadded:: 2.3
28
29This module defines functions and classes which implement a flexible event
30logging system for applications and libraries.
31
32The key benefit of having the logging API provided by a standard library module
33is that all Python modules can participate in logging, so your application log
34can include your own messages integrated with messages from third-party
35modules.
36
37The module provides a lot of functionality and flexibility.  If you are
38unfamiliar with logging, the best way to get to grips with it is to see the
39tutorials (see the links on the right).
40
41The basic classes defined by the module, together with their functions, are
42listed below.
43
44* Loggers expose the interface that application code directly uses.
45* Handlers send the log records (created by loggers) to the appropriate
46  destination.
47* Filters provide a finer grained facility for determining which log records
48  to output.
49* Formatters specify the layout of log records in the final output.
50
51
52.. _logger:
53
54Logger Objects
55--------------
56
57Loggers have the following attributes and methods.  Note that Loggers are never
58instantiated directly, but always through the module-level function
59``logging.getLogger(name)``.  Multiple calls to :func:`getLogger` with the same
60name will always return a reference to the same Logger object.
61
62The ``name`` is potentially a period-separated hierarchical value, like
63``foo.bar.baz`` (though it could also be just plain ``foo``, for example).
64Loggers that are further down in the hierarchical list are children of loggers
65higher up in the list.  For example, given a logger with a name of ``foo``,
66loggers with names of ``foo.bar``, ``foo.bar.baz``, and ``foo.bam`` are all
67descendants of ``foo``.  The logger name hierarchy is analogous to the Python
68package hierarchy, and identical to it if you organise your loggers on a
69per-module basis using the recommended construction
70``logging.getLogger(__name__)``.  That's because in a module, ``__name__``
71is the module's name in the Python package namespace.
72
73
74.. class:: Logger
75
76.. attribute:: Logger.propagate
77
78   If this evaluates to true, events logged to this logger will be passed to the
79   handlers of higher level (ancestor) loggers, in addition to any handlers
80   attached to this logger. Messages are passed directly to the ancestor
81   loggers' handlers - neither the level nor filters of the ancestor loggers in
82   question are considered.
83
84   If this evaluates to false, logging messages are not passed to the handlers
85   of ancestor loggers.
86
87   The constructor sets this attribute to ``True``.
88
89   .. note:: If you attach a handler to a logger *and* one or more of its
90      ancestors, it may emit the same record multiple times. In general, you
91      should not need to attach a handler to more than one logger - if you just
92      attach it to the appropriate logger which is highest in the logger
93      hierarchy, then it will see all events logged by all descendant loggers,
94      provided that their propagate setting is left set to ``True``. A common
95      scenario is to attach handlers only to the root logger, and to let
96      propagation take care of the rest.
97
98.. method:: Logger.setLevel(level)
99
100   Sets the threshold for this logger to *level*. Logging messages which are less
101   severe than *level* will be ignored. When a logger is created, the level is set to
102   :const:`NOTSET` (which causes all messages to be processed when the logger is
103   the root logger, or delegation to the parent when the logger is a non-root
104   logger). Note that the root logger is created with level :const:`WARNING`.
105
106   The term 'delegation to the parent' means that if a logger has a level of
107   NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
108   a level other than NOTSET is found, or the root is reached.
109
110   If an ancestor is found with a level other than NOTSET, then that ancestor's
111   level is treated as the effective level of the logger where the ancestor search
112   began, and is used to determine how a logging event is handled.
113
114   If the root is reached, and it has a level of NOTSET, then all messages will be
115   processed. Otherwise, the root's level will be used as the effective level.
116
117   See :ref:`levels` for a list of levels.
118
119
120.. method:: Logger.isEnabledFor(lvl)
121
122   Indicates if a message of severity *lvl* would be processed by this logger.
123   This method checks first the module-level level set by
124   ``logging.disable(lvl)`` and then the logger's effective level as determined
125   by :meth:`getEffectiveLevel`.
126
127
128.. method:: Logger.getEffectiveLevel()
129
130   Indicates the effective level for this logger. If a value other than
131   :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
132   the hierarchy is traversed towards the root until a value other than
133   :const:`NOTSET` is found, and that value is returned. The value returned is
134   an integer, typically one of :const:`logging.DEBUG`, :const:`logging.INFO`
135   etc.
136
137
138.. method:: Logger.getChild(suffix)
139
140   Returns a logger which is a descendant to this logger, as determined by the suffix.
141   Thus, ``logging.getLogger('abc').getChild('def.ghi')`` would return the same
142   logger as would be returned by ``logging.getLogger('abc.def.ghi')``. This is a
143   convenience method, useful when the parent logger is named using e.g. ``__name__``
144   rather than a literal string.
145
146   .. versionadded:: 2.7
147
148
149.. method:: Logger.debug(msg, *args, **kwargs)
150
151   Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
152   message format string, and the *args* are the arguments which are merged into
153   *msg* using the string formatting operator. (Note that this means that you can
154   use keywords in the format string, together with a single dictionary argument.)
155
156   There are two keyword arguments in *kwargs* which are inspected: *exc_info*
157   which, if it does not evaluate as false, causes exception information to be
158   added to the logging message. If an exception tuple (in the format returned by
159   :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
160   is called to get the exception information.
161
162   The second keyword argument is *extra* which can be used to pass a
163   dictionary which is used to populate the __dict__ of the LogRecord created for
164   the logging event with user-defined attributes. These custom attributes can then
165   be used as you like. For example, they could be incorporated into logged
166   messages. For example::
167
168      FORMAT = '%(asctime)-15s %(clientip)s %(user)-8s %(message)s'
169      logging.basicConfig(format=FORMAT)
170      d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
171      logger = logging.getLogger('tcpserver')
172      logger.warning('Protocol problem: %s', 'connection reset', extra=d)
173
174   would print something like  ::
175
176      2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset
177
178   The keys in the dictionary passed in *extra* should not clash with the keys used
179   by the logging system. (See the :class:`Formatter` documentation for more
180   information on which keys are used by the logging system.)
181
182   If you choose to use these attributes in logged messages, you need to exercise
183   some care. In the above example, for instance, the :class:`Formatter` has been
184   set up with a format string which expects 'clientip' and 'user' in the attribute
185   dictionary of the LogRecord. If these are missing, the message will not be
186   logged because a string formatting exception will occur. So in this case, you
187   always need to pass the *extra* dictionary with these keys.
188
189   While this might be annoying, this feature is intended for use in specialized
190   circumstances, such as multi-threaded servers where the same code executes in
191   many contexts, and interesting conditions which arise are dependent on this
192   context (such as remote client IP address and authenticated user name, in the
193   above example). In such circumstances, it is likely that specialized
194   :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
195
196
197.. method:: Logger.info(msg, *args, **kwargs)
198
199   Logs a message with level :const:`INFO` on this logger. The arguments are
200   interpreted as for :meth:`debug`.
201
202
203.. method:: Logger.warning(msg, *args, **kwargs)
204
205   Logs a message with level :const:`WARNING` on this logger. The arguments are
206   interpreted as for :meth:`debug`.
207
208
209.. method:: Logger.error(msg, *args, **kwargs)
210
211   Logs a message with level :const:`ERROR` on this logger. The arguments are
212   interpreted as for :meth:`debug`.
213
214
215.. method:: Logger.critical(msg, *args, **kwargs)
216
217   Logs a message with level :const:`CRITICAL` on this logger. The arguments are
218   interpreted as for :meth:`debug`.
219
220
221.. method:: Logger.log(lvl, msg, *args, **kwargs)
222
223   Logs a message with integer level *lvl* on this logger. The other arguments are
224   interpreted as for :meth:`debug`.
225
226
227.. method:: Logger.exception(msg, *args, **kwargs)
228
229   Logs a message with level :const:`ERROR` on this logger. The arguments are
230   interpreted as for :meth:`debug`, except that any passed *exc_info* is not
231   inspected. Exception info is always added to the logging message. This method
232   should only be called from an exception handler.
233
234
235.. method:: Logger.addFilter(filter)
236
237   Adds the specified filter *filter* to this logger.
238
239
240.. method:: Logger.removeFilter(filter)
241
242   Removes the specified filter *filter* from this logger.
243
244
245.. method:: Logger.filter(record)
246
247   Applies this logger's filters to the record and returns a true value if the
248   record is to be processed. The filters are consulted in turn, until one of
249   them returns a false value. If none of them return a false value, the record
250   will be processed (passed to handlers). If one returns a false value, no
251   further processing of the record occurs.
252
253
254.. method:: Logger.addHandler(hdlr)
255
256   Adds the specified handler *hdlr* to this logger.
257
258
259.. method:: Logger.removeHandler(hdlr)
260
261   Removes the specified handler *hdlr* from this logger.
262
263
264.. method:: Logger.findCaller()
265
266   Finds the caller's source filename and line number. Returns the filename, line
267   number and function name as a 3-element tuple.
268
269   .. versionchanged:: 2.4
270      The function name was added. In earlier versions, the filename and line
271      number were returned as a 2-element tuple.
272
273.. method:: Logger.handle(record)
274
275   Handles a record by passing it to all handlers associated with this logger and
276   its ancestors (until a false value of *propagate* is found). This method is used
277   for unpickled records received from a socket, as well as those created locally.
278   Logger-level filtering is applied using :meth:`~Logger.filter`.
279
280
281.. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info, func=None, extra=None)
282
283   This is a factory method which can be overridden in subclasses to create
284   specialized :class:`LogRecord` instances.
285
286   .. versionchanged:: 2.5
287      *func* and *extra* were added.
288
289
290.. _levels:
291
292Logging Levels
293--------------
294
295The numeric values of logging levels are given in the following table. These are
296primarily of interest if you want to define your own levels, and need them to
297have specific values relative to the predefined levels. If you define a level
298with the same numeric value, it overwrites the predefined value; the predefined
299name is lost.
300
301+--------------+---------------+
302| Level        | Numeric value |
303+==============+===============+
304| ``CRITICAL`` | 50            |
305+--------------+---------------+
306| ``ERROR``    | 40            |
307+--------------+---------------+
308| ``WARNING``  | 30            |
309+--------------+---------------+
310| ``INFO``     | 20            |
311+--------------+---------------+
312| ``DEBUG``    | 10            |
313+--------------+---------------+
314| ``NOTSET``   | 0             |
315+--------------+---------------+
316
317
318.. _handler:
319
320Handler Objects
321---------------
322
323Handlers have the following attributes and methods. Note that :class:`Handler`
324is never instantiated directly; this class acts as a base for more useful
325subclasses. However, the :meth:`__init__` method in subclasses needs to call
326:meth:`Handler.__init__`.
327
328
329.. method:: Handler.__init__(level=NOTSET)
330
331   Initializes the :class:`Handler` instance by setting its level, setting the list
332   of filters to the empty list and creating a lock (using :meth:`createLock`) for
333   serializing access to an I/O mechanism.
334
335
336.. method:: Handler.createLock()
337
338   Initializes a thread lock which can be used to serialize access to underlying
339   I/O functionality which may not be threadsafe.
340
341
342.. method:: Handler.acquire()
343
344   Acquires the thread lock created with :meth:`createLock`.
345
346
347.. method:: Handler.release()
348
349   Releases the thread lock acquired with :meth:`acquire`.
350
351
352.. method:: Handler.setLevel(level)
353
354   Sets the threshold for this handler to *level*. Logging messages which are less
355   severe than *level* will be ignored. When a handler is created, the level is set
356   to :const:`NOTSET` (which causes all messages to be processed).
357
358   See :ref:`levels` for a list of levels.
359
360.. method:: Handler.setFormatter(fmt)
361
362   Sets the :class:`Formatter` for this handler to *fmt*.
363
364
365.. method:: Handler.addFilter(filter)
366
367   Adds the specified filter *filter* to this handler.
368
369
370.. method:: Handler.removeFilter(filter)
371
372   Removes the specified filter *filter* from this handler.
373
374
375.. method:: Handler.filter(record)
376
377   Applies this handler's filters to the record and returns a true value if the
378   record is to be processed. The filters are consulted in turn, until one of
379   them returns a false value. If none of them return a false value, the record
380   will be emitted. If one returns a false value, the handler will not emit the
381   record.
382
383
384.. method:: Handler.flush()
385
386   Ensure all logging output has been flushed. This version does nothing and is
387   intended to be implemented by subclasses.
388
389
390.. method:: Handler.close()
391
392   Tidy up any resources used by the handler. This version does no output but
393   removes the handler from an internal list of handlers which is closed when
394   :func:`shutdown` is called. Subclasses should ensure that this gets called
395   from overridden :meth:`close` methods.
396
397
398.. method:: Handler.handle(record)
399
400   Conditionally emits the specified logging record, depending on filters which may
401   have been added to the handler. Wraps the actual emission of the record with
402   acquisition/release of the I/O thread lock.
403
404
405.. method:: Handler.handleError(record)
406
407   This method should be called from handlers when an exception is encountered
408   during an :meth:`emit` call. If the module-level attribute
409   ``raiseExceptions`` is ``False``, exceptions get silently ignored. This is
410   what is mostly wanted for a logging system - most users will not care about
411   errors in the logging system, they are more interested in application
412   errors. You could, however, replace this with a custom handler if you wish.
413   The specified record is the one which was being processed when the exception
414   occurred. (The default value of ``raiseExceptions`` is ``True``, as that is
415   more useful during development).
416
417
418.. method:: Handler.format(record)
419
420   Do formatting for a record - if a formatter is set, use it. Otherwise, use the
421   default formatter for the module.
422
423
424.. method:: Handler.emit(record)
425
426   Do whatever it takes to actually log the specified logging record. This version
427   is intended to be implemented by subclasses and so raises a
428   :exc:`NotImplementedError`.
429
430For a list of handlers included as standard, see :mod:`logging.handlers`.
431
432.. _formatter-objects:
433
434Formatter Objects
435-----------------
436
437.. currentmodule:: logging
438
439:class:`Formatter` objects have the following attributes and methods. They are
440responsible for converting a :class:`LogRecord` to (usually) a string which can
441be interpreted by either a human or an external system. The base
442:class:`Formatter` allows a formatting string to be specified. If none is
443supplied, the default value of ``'%(message)s'`` is used, which just includes
444the message in the logging call. To have additional items of information in the
445formatted output (such as a timestamp), keep reading.
446
447A Formatter can be initialized with a format string which makes use of knowledge
448of the :class:`LogRecord` attributes - such as the default value mentioned above
449making use of the fact that the user's message and arguments are pre-formatted
450into a :class:`LogRecord`'s *message* attribute.  This format string contains
451standard Python %-style mapping keys. See section :ref:`string-formatting`
452for more information on string formatting.
453
454The useful mapping keys in a :class:`LogRecord` are given in the section on
455:ref:`logrecord-attributes`.
456
457
458.. class:: Formatter(fmt=None, datefmt=None)
459
460   Returns a new instance of the :class:`Formatter` class.  The instance is
461   initialized with a format string for the message as a whole, as well as a
462   format string for the date/time portion of a message.  If no *fmt* is
463   specified, ``'%(message)s'`` is used.  If no *datefmt* is specified, the
464   ISO8601 date format is used.
465
466   .. method:: format(record)
467
468      The record's attribute dictionary is used as the operand to a string
469      formatting operation. Returns the resulting string. Before formatting the
470      dictionary, a couple of preparatory steps are carried out. The *message*
471      attribute of the record is computed using *msg* % *args*. If the
472      formatting string contains ``'(asctime)'``, :meth:`formatTime` is called
473      to format the event time. If there is exception information, it is
474      formatted using :meth:`formatException` and appended to the message. Note
475      that the formatted exception information is cached in attribute
476      *exc_text*. This is useful because the exception information can be
477      pickled and sent across the wire, but you should be careful if you have
478      more than one :class:`Formatter` subclass which customizes the formatting
479      of exception information. In this case, you will have to clear the cached
480      value after a formatter has done its formatting, so that the next
481      formatter to handle the event doesn't use the cached value but
482      recalculates it afresh.
483
484
485   .. method:: formatTime(record, datefmt=None)
486
487      This method should be called from :meth:`format` by a formatter which
488      wants to make use of a formatted time. This method can be overridden in
489      formatters to provide for any specific requirement, but the basic behavior
490      is as follows: if *datefmt* (a string) is specified, it is used with
491      :func:`time.strftime` to format the creation time of the
492      record. Otherwise, the ISO8601 format is used.  The resulting string is
493      returned.
494
495      This function uses a user-configurable function to convert the creation
496      time to a tuple. By default, :func:`time.localtime` is used; to change
497      this for a particular formatter instance, set the ``converter`` attribute
498      to a function with the same signature as :func:`time.localtime` or
499      :func:`time.gmtime`. To change it for all formatters, for example if you
500      want all logging times to be shown in GMT, set the ``converter``
501      attribute in the ``Formatter`` class.
502
503   .. method:: formatException(exc_info)
504
505      Formats the specified exception information (a standard exception tuple as
506      returned by :func:`sys.exc_info`) as a string. This default implementation
507      just uses :func:`traceback.print_exception`. The resulting string is
508      returned.
509
510.. _filter:
511
512Filter Objects
513--------------
514
515``Filters`` can be used by ``Handlers`` and ``Loggers`` for more sophisticated
516filtering than is provided by levels. The base filter class only allows events
517which are below a certain point in the logger hierarchy. For example, a filter
518initialized with 'A.B' will allow events logged by loggers 'A.B', 'A.B.C',
519'A.B.C.D', 'A.B.D' etc. but not 'A.BB', 'B.A.B' etc. If initialized with the
520empty string, all events are passed.
521
522
523.. class:: Filter(name='')
524
525   Returns an instance of the :class:`Filter` class. If *name* is specified, it
526   names a logger which, together with its children, will have its events allowed
527   through the filter. If *name* is the empty string, allows every event.
528
529
530   .. method:: filter(record)
531
532      Is the specified record to be logged? Returns zero for no, nonzero for
533      yes. If deemed appropriate, the record may be modified in-place by this
534      method.
535
536Note that filters attached to handlers are consulted before an event is
537emitted by the handler, whereas filters attached to loggers are consulted
538whenever an event is logged (using :meth:`debug`, :meth:`info`,
539etc.), before sending an event to handlers. This means that events which have
540been generated by descendant loggers will not be filtered by a logger's filter
541setting, unless the filter has also been applied to those descendant loggers.
542
543You don't actually need to subclass ``Filter``: you can pass any instance
544which has a ``filter`` method with the same semantics.
545
546Although filters are used primarily to filter records based on more
547sophisticated criteria than levels, they get to see every record which is
548processed by the handler or logger they're attached to: this can be useful if
549you want to do things like counting how many records were processed by a
550particular logger or handler, or adding, changing or removing attributes in
551the LogRecord being processed. Obviously changing the LogRecord needs to be
552done with some care, but it does allow the injection of contextual information
553into logs (see :ref:`filters-contextual`).
554
555.. _log-record:
556
557LogRecord Objects
558-----------------
559
560:class:`LogRecord` instances are created automatically by the :class:`Logger`
561every time something is logged, and can be created manually via
562:func:`makeLogRecord` (for example, from a pickled event received over the
563wire).
564
565
566.. class:: LogRecord(name, level, pathname, lineno, msg, args, exc_info, func=None)
567
568   Contains all the information pertinent to the event being logged.
569
570   The primary information is passed in :attr:`msg` and :attr:`args`, which
571   are combined using ``msg % args`` to create the :attr:`message` field of the
572   record.
573
574   :param name:  The name of the logger used to log the event represented by
575                 this LogRecord. Note that this name will always have this
576                 value, even though it may be emitted by a handler attached to
577                 a different (ancestor) logger.
578   :param level: The numeric level of the logging event (one of DEBUG, INFO etc.)
579                 Note that this is converted to *two* attributes of the LogRecord:
580                 ``levelno`` for the numeric value and ``levelname`` for the
581                 corresponding level name.
582   :param pathname: The full pathname of the source file where the logging call
583                    was made.
584   :param lineno: The line number in the source file where the logging call was
585                  made.
586   :param msg: The event description message, possibly a format string with
587               placeholders for variable data.
588   :param args: Variable data to merge into the *msg* argument to obtain the
589                event description.
590   :param exc_info: An exception tuple with the current exception information,
591                    or ``None`` if no exception information is available.
592   :param func: The name of the function or method from which the logging call
593                was invoked.
594
595   .. versionchanged:: 2.5
596      *func* was added.
597
598   .. method:: getMessage()
599
600      Returns the message for this :class:`LogRecord` instance after merging any
601      user-supplied arguments with the message. If the user-supplied message
602      argument to the logging call is not a string, :func:`str` is called on it to
603      convert it to a string. This allows use of user-defined classes as
604      messages, whose ``__str__`` method can return the actual format string to
605      be used.
606
607
608.. _logrecord-attributes:
609
610LogRecord attributes
611--------------------
612
613The LogRecord has a number of attributes, most of which are derived from the
614parameters to the constructor. (Note that the names do not always correspond
615exactly between the LogRecord constructor parameters and the LogRecord
616attributes.) These attributes can be used to merge data from the record into
617the format string. The following table lists (in alphabetical order) the
618attribute names, their meanings and the corresponding placeholder in a %-style
619format string.
620
621+----------------+-------------------------+-----------------------------------------------+
622| Attribute name | Format                  | Description                                   |
623+================+=========================+===============================================+
624| args           | You shouldn't need to   | The tuple of arguments merged into ``msg`` to |
625|                | format this yourself.   | produce ``message``, or a dict whose values   |
626|                |                         | are used for the merge (when there is only one|
627|                |                         | argument, and it is a dictionary).            |
628+----------------+-------------------------+-----------------------------------------------+
629| asctime        | ``%(asctime)s``         | Human-readable time when the                  |
630|                |                         | :class:`LogRecord` was created.  By default   |
631|                |                         | this is of the form '2003-07-08 16:49:45,896' |
632|                |                         | (the numbers after the comma are millisecond  |
633|                |                         | portion of the time).                         |
634+----------------+-------------------------+-----------------------------------------------+
635| created        | ``%(created)f``         | Time when the :class:`LogRecord` was created  |
636|                |                         | (as returned by :func:`time.time`).           |
637+----------------+-------------------------+-----------------------------------------------+
638| exc_info       | You shouldn't need to   | Exception tuple (à la ``sys.exc_info``) or,   |
639|                | format this yourself.   | if no exception has occurred, ``None``.       |
640+----------------+-------------------------+-----------------------------------------------+
641| filename       | ``%(filename)s``        | Filename portion of ``pathname``.             |
642+----------------+-------------------------+-----------------------------------------------+
643| funcName       | ``%(funcName)s``        | Name of function containing the logging call. |
644+----------------+-------------------------+-----------------------------------------------+
645| levelname      | ``%(levelname)s``       | Text logging level for the message            |
646|                |                         | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``,      |
647|                |                         | ``'ERROR'``, ``'CRITICAL'``).                 |
648+----------------+-------------------------+-----------------------------------------------+
649| levelno        | ``%(levelno)s``         | Numeric logging level for the message         |
650|                |                         | (:const:`DEBUG`, :const:`INFO`,               |
651|                |                         | :const:`WARNING`, :const:`ERROR`,             |
652|                |                         | :const:`CRITICAL`).                           |
653+----------------+-------------------------+-----------------------------------------------+
654| lineno         | ``%(lineno)d``          | Source line number where the logging call was |
655|                |                         | issued (if available).                        |
656+----------------+-------------------------+-----------------------------------------------+
657| module         | ``%(module)s``          | Module (name portion of ``filename``).        |
658+----------------+-------------------------+-----------------------------------------------+
659| msecs          | ``%(msecs)d``           | Millisecond portion of the time when the      |
660|                |                         | :class:`LogRecord` was created.               |
661+----------------+-------------------------+-----------------------------------------------+
662| message        | ``%(message)s``         | The logged message, computed as ``msg %       |
663|                |                         | args``. This is set when                      |
664|                |                         | :meth:`Formatter.format` is invoked.          |
665+----------------+-------------------------+-----------------------------------------------+
666| msg            | You shouldn't need to   | The format string passed in the original      |
667|                | format this yourself.   | logging call. Merged with ``args`` to         |
668|                |                         | produce ``message``, or an arbitrary object   |
669|                |                         | (see :ref:`arbitrary-object-messages`).       |
670+----------------+-------------------------+-----------------------------------------------+
671| name           | ``%(name)s``            | Name of the logger used to log the call.      |
672+----------------+-------------------------+-----------------------------------------------+
673| pathname       | ``%(pathname)s``        | Full pathname of the source file where the    |
674|                |                         | logging call was issued (if available).       |
675+----------------+-------------------------+-----------------------------------------------+
676| process        | ``%(process)d``         | Process ID (if available).                    |
677+----------------+-------------------------+-----------------------------------------------+
678| processName    | ``%(processName)s``     | Process name (if available).                  |
679+----------------+-------------------------+-----------------------------------------------+
680| relativeCreated| ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was   |
681|                |                         | created, relative to the time the logging     |
682|                |                         | module was loaded.                            |
683+----------------+-------------------------+-----------------------------------------------+
684| thread         | ``%(thread)d``          | Thread ID (if available).                     |
685+----------------+-------------------------+-----------------------------------------------+
686| threadName     | ``%(threadName)s``      | Thread name (if available).                   |
687+----------------+-------------------------+-----------------------------------------------+
688
689.. versionchanged:: 2.5
690   *funcName* was added.
691
692.. versionchanged:: 2.6
693   *processName* was added.
694
695.. _logger-adapter:
696
697LoggerAdapter Objects
698---------------------
699
700:class:`LoggerAdapter` instances are used to conveniently pass contextual
701information into logging calls. For a usage example, see the section on
702:ref:`adding contextual information to your logging output <context-info>`.
703
704.. versionadded:: 2.6
705
706
707.. class:: LoggerAdapter(logger, extra)
708
709   Returns an instance of :class:`LoggerAdapter` initialized with an
710   underlying :class:`Logger` instance and a dict-like object.
711
712   .. method:: process(msg, kwargs)
713
714      Modifies the message and/or keyword arguments passed to a logging call in
715      order to insert contextual information. This implementation takes the object
716      passed as *extra* to the constructor and adds it to *kwargs* using key
717      'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
718      (possibly modified) versions of the arguments passed in.
719
720In addition to the above, :class:`LoggerAdapter` supports the following
721methods of :class:`Logger`: :meth:`~Logger.debug`, :meth:`~Logger.info`,
722:meth:`~Logger.warning`, :meth:`~Logger.error`, :meth:`~Logger.exception`,
723:meth:`~Logger.critical`, :meth:`~Logger.log` and :meth:`~Logger.isEnabledFor`.
724These methods have the same signatures as their counterparts in :class:`Logger`,
725so you can use the two types of instances interchangeably for these calls.
726
727.. versionchanged:: 2.7
728   The :meth:`~Logger.isEnabledFor` method was added to :class:`LoggerAdapter`.
729   This method delegates to the underlying logger.
730
731
732Thread Safety
733-------------
734
735The logging module is intended to be thread-safe without any special work
736needing to be done by its clients. It achieves this though using threading
737locks; there is one lock to serialize access to the module's shared data, and
738each handler also creates a lock to serialize access to its underlying I/O.
739
740If you are implementing asynchronous signal handlers using the :mod:`signal`
741module, you may not be able to use logging from within such handlers. This is
742because lock implementations in the :mod:`threading` module are not always
743re-entrant, and so cannot be invoked from such signal handlers.
744
745
746Module-Level Functions
747----------------------
748
749In addition to the classes described above, there are a number of module- level
750functions.
751
752
753.. function:: getLogger([name])
754
755   Return a logger with the specified name or, if no name is specified, return a
756   logger which is the root logger of the hierarchy. If specified, the name is
757   typically a dot-separated hierarchical name like *"a"*, *"a.b"* or *"a.b.c.d"*.
758   Choice of these names is entirely up to the developer who is using logging.
759
760   All calls to this function with a given name return the same logger instance.
761   This means that logger instances never need to be passed between different parts
762   of an application.
763
764
765.. function:: getLoggerClass()
766
767   Return either the standard :class:`Logger` class, or the last class passed to
768   :func:`setLoggerClass`. This function may be called from within a new class
769   definition, to ensure that installing a customized :class:`Logger` class will
770   not undo customizations already applied by other code. For example::
771
772      class MyLogger(logging.getLoggerClass()):
773          # ... override behaviour here
774
775
776.. function:: debug(msg[, *args[, **kwargs]])
777
778   Logs a message with level :const:`DEBUG` on the root logger. The *msg* is the
779   message format string, and the *args* are the arguments which are merged into
780   *msg* using the string formatting operator. (Note that this means that you can
781   use keywords in the format string, together with a single dictionary argument.)
782
783   There are two keyword arguments in *kwargs* which are inspected: *exc_info*
784   which, if it does not evaluate as false, causes exception information to be
785   added to the logging message. If an exception tuple (in the format returned by
786   :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
787   is called to get the exception information.
788
789   The other optional keyword argument is *extra* which can be used to pass a
790   dictionary which is used to populate the __dict__ of the LogRecord created for
791   the logging event with user-defined attributes. These custom attributes can then
792   be used as you like. For example, they could be incorporated into logged
793   messages. For example::
794
795      FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
796      logging.basicConfig(format=FORMAT)
797      d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
798      logging.warning("Protocol problem: %s", "connection reset", extra=d)
799
800   would print something like::
801
802      2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset
803
804   The keys in the dictionary passed in *extra* should not clash with the keys used
805   by the logging system. (See the :class:`Formatter` documentation for more
806   information on which keys are used by the logging system.)
807
808   If you choose to use these attributes in logged messages, you need to exercise
809   some care. In the above example, for instance, the :class:`Formatter` has been
810   set up with a format string which expects 'clientip' and 'user' in the attribute
811   dictionary of the LogRecord. If these are missing, the message will not be
812   logged because a string formatting exception will occur. So in this case, you
813   always need to pass the *extra* dictionary with these keys.
814
815   While this might be annoying, this feature is intended for use in specialized
816   circumstances, such as multi-threaded servers where the same code executes in
817   many contexts, and interesting conditions which arise are dependent on this
818   context (such as remote client IP address and authenticated user name, in the
819   above example). In such circumstances, it is likely that specialized
820   :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
821
822   .. versionchanged:: 2.5
823      *extra* was added.
824
825
826.. function:: info(msg[, *args[, **kwargs]])
827
828   Logs a message with level :const:`INFO` on the root logger. The arguments are
829   interpreted as for :func:`debug`.
830
831
832.. function:: warning(msg[, *args[, **kwargs]])
833
834   Logs a message with level :const:`WARNING` on the root logger. The arguments are
835   interpreted as for :func:`debug`.
836
837
838.. function:: error(msg[, *args[, **kwargs]])
839
840   Logs a message with level :const:`ERROR` on the root logger. The arguments are
841   interpreted as for :func:`debug`.
842
843
844.. function:: critical(msg[, *args[, **kwargs]])
845
846   Logs a message with level :const:`CRITICAL` on the root logger. The arguments
847   are interpreted as for :func:`debug`.
848
849
850.. function:: exception(msg[, *args[, **kwargs]])
851
852   Logs a message with level :const:`ERROR` on the root logger. The arguments are
853   interpreted as for :func:`debug`, except that any passed *exc_info* is not
854   inspected. Exception info is always added to the logging message. This
855   function should only be called from an exception handler.
856
857
858.. function:: log(level, msg[, *args[, **kwargs]])
859
860   Logs a message with level *level* on the root logger. The other arguments are
861   interpreted as for :func:`debug`.
862
863   .. note:: The above module-level convenience functions, which delegate to the
864      root logger, call :func:`basicConfig` to ensure that at least one handler
865      is available. Because of this, they should *not* be used in threads,
866      in versions of Python earlier than 2.7.1 and 3.2, unless at least one
867      handler has been added to the root logger *before* the threads are
868      started. In earlier versions of Python, due to a thread safety shortcoming
869      in :func:`basicConfig`, this can (under rare circumstances) lead to
870      handlers being added multiple times to the root logger, which can in turn
871      lead to multiple messages for the same event.
872
873.. function:: disable(lvl)
874
875   Provides an overriding level *lvl* for all loggers which takes precedence over
876   the logger's own level. When the need arises to temporarily throttle logging
877   output down across the whole application, this function can be useful. Its
878   effect is to disable all logging calls of severity *lvl* and below, so that
879   if you call it with a value of INFO, then all INFO and DEBUG events would be
880   discarded, whereas those of severity WARNING and above would be processed
881   according to the logger's effective level. If
882   ``logging.disable(logging.NOTSET)`` is called, it effectively removes this
883   overriding level, so that logging output again depends on the effective
884   levels of individual loggers.
885
886
887.. function:: addLevelName(lvl, levelName)
888
889   Associates level *lvl* with text *levelName* in an internal dictionary, which is
890   used to map numeric levels to a textual representation, for example when a
891   :class:`Formatter` formats a message. This function can also be used to define
892   your own levels. The only constraints are that all levels used must be
893   registered using this function, levels should be positive integers and they
894   should increase in increasing order of severity.
895
896   .. note:: If you are thinking of defining your own levels, please see the
897      section on :ref:`custom-levels`.
898
899.. function:: getLevelName(lvl)
900
901   Returns the textual representation of logging level *lvl*. If the level is one
902   of the predefined levels :const:`CRITICAL`, :const:`ERROR`, :const:`WARNING`,
903   :const:`INFO` or :const:`DEBUG` then you get the corresponding string. If you
904   have associated levels with names using :func:`addLevelName` then the name you
905   have associated with *lvl* is returned. If a numeric value corresponding to one
906   of the defined levels is passed in, the corresponding string representation is
907   returned. Otherwise, the string "Level %s" % lvl is returned.
908
909   .. note:: Integer levels should be used when e.g. setting levels on instances
910      of :class:`Logger` and handlers. This function is used to convert between
911      an integer level and the level name displayed in the formatted log output
912      by means of the ``%(levelname)s`` format specifier (see
913      :ref:`logrecord-attributes`).
914
915
916.. function:: makeLogRecord(attrdict)
917
918   Creates and returns a new :class:`LogRecord` instance whose attributes are
919   defined by *attrdict*. This function is useful for taking a pickled
920   :class:`LogRecord` attribute dictionary, sent over a socket, and reconstituting
921   it as a :class:`LogRecord` instance at the receiving end.
922
923
924.. function:: basicConfig([**kwargs])
925
926   Does basic configuration for the logging system by creating a
927   :class:`StreamHandler` with a default :class:`Formatter` and adding it to the
928   root logger. The functions :func:`debug`, :func:`info`, :func:`warning`,
929   :func:`error` and :func:`critical` will call :func:`basicConfig` automatically
930   if no handlers are defined for the root logger.
931
932   This function does nothing if the root logger already has handlers
933   configured for it.
934
935   .. versionchanged:: 2.4
936      Formerly, :func:`basicConfig` did not take any keyword arguments.
937
938   .. note:: This function should be called from the main thread before other
939      threads are started. In versions of Python prior to 2.7.1 and 3.2, if
940      this function is called from multiple threads, it is possible (in rare
941      circumstances) that a handler will be added to the root logger more than
942      once, leading to unexpected results such as messages being duplicated in
943      the log.
944
945   The following keyword arguments are supported.
946
947   .. tabularcolumns:: |l|L|
948
949   +--------------+---------------------------------------------+
950   | Format       | Description                                 |
951   +==============+=============================================+
952   | *filename*   | Specifies that a FileHandler be created,    |
953   |              | using the specified filename, rather than a |
954   |              | StreamHandler.                              |
955   +--------------+---------------------------------------------+
956   | *filemode*   | If *filename* is specified, open the file   |
957   |              | in this mode. Defaults to ``'a'``.          |
958   +--------------+---------------------------------------------+
959   | *format*     | Use the specified format string for the     |
960   |              | handler.                                    |
961   +--------------+---------------------------------------------+
962   | *datefmt*    | Use the specified date/time format, as      |
963   |              | accepted by :func:`time.strftime`.          |
964   +--------------+---------------------------------------------+
965   | *level*      | Set the root logger level to the specified  |
966   |              | :ref:`level <levels>`.                      |
967   +--------------+---------------------------------------------+
968   | *stream*     | Use the specified stream to initialize the  |
969   |              | StreamHandler. Note that this argument is   |
970   |              | incompatible with *filename* - if both are  |
971   |              | present, *stream* is ignored.               |
972   +--------------+---------------------------------------------+
973
974
975.. function:: shutdown()
976
977   Informs the logging system to perform an orderly shutdown by flushing and
978   closing all handlers. This should be called at application exit and no
979   further use of the logging system should be made after this call.
980
981
982.. function:: setLoggerClass(klass)
983
984   Tells the logging system to use the class *klass* when instantiating a logger.
985   The class should define :meth:`__init__` such that only a name argument is
986   required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
987   function is typically called before any loggers are instantiated by applications
988   which need to use custom logger behavior.
989
990
991Integration with the warnings module
992------------------------------------
993
994The :func:`captureWarnings` function can be used to integrate :mod:`logging`
995with the :mod:`warnings` module.
996
997.. function:: captureWarnings(capture)
998
999   This function is used to turn the capture of warnings by logging on and
1000   off.
1001
1002   If *capture* is ``True``, warnings issued by the :mod:`warnings` module will
1003   be redirected to the logging system. Specifically, a warning will be
1004   formatted using :func:`warnings.formatwarning` and the resulting string
1005   logged to a logger named ``'py.warnings'`` with a severity of :const:`WARNING`.
1006
1007   If *capture* is ``False``, the redirection of warnings to the logging system
1008   will stop, and warnings will be redirected to their original destinations
1009   (i.e. those in effect before ``captureWarnings(True)`` was called).
1010
1011
1012.. seealso::
1013
1014   Module :mod:`logging.config`
1015      Configuration API for the logging module.
1016
1017   Module :mod:`logging.handlers`
1018      Useful handlers included with the logging module.
1019
1020   :pep:`282` - A Logging System
1021      The proposal which described this feature for inclusion in the Python standard
1022      library.
1023
1024   `Original Python logging package <https://www.red-dove.com/python_logging.html>`_
1025      This is the original source for the :mod:`logging` package.  The version of the
1026      package available from this site is suitable for use with Python 1.5.2, 2.1.x
1027      and 2.2.x, which do not include the :mod:`logging` package in the standard
1028      library.
1029
1030