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Georg Brandl8ec7f652007-08-15 14:28:01 +00001:mod:`logging` --- Logging facility for Python
2==============================================
3
4.. module:: logging
5 :synopsis: Flexible error logging system for applications.
6
7
8.. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
9.. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
10
11
Georg Brandl8ec7f652007-08-15 14:28:01 +000012.. index:: pair: Errors; logging
13
14.. versionadded:: 2.3
15
16This module defines functions and classes which implement a flexible error
17logging system for applications.
18
19Logging is performed by calling methods on instances of the :class:`Logger`
20class (hereafter called :dfn:`loggers`). Each instance has a name, and they are
Georg Brandla7395032007-10-21 12:15:05 +000021conceptually arranged in a namespace hierarchy using dots (periods) as
Georg Brandl8ec7f652007-08-15 14:28:01 +000022separators. For example, a logger named "scan" is the parent of loggers
23"scan.text", "scan.html" and "scan.pdf". Logger names can be anything you want,
24and indicate the area of an application in which a logged message originates.
25
26Logged messages also have levels of importance associated with them. The default
27levels provided are :const:`DEBUG`, :const:`INFO`, :const:`WARNING`,
28:const:`ERROR` and :const:`CRITICAL`. As a convenience, you indicate the
29importance of a logged message by calling an appropriate method of
30:class:`Logger`. The methods are :meth:`debug`, :meth:`info`, :meth:`warning`,
31:meth:`error` and :meth:`critical`, which mirror the default levels. You are not
32constrained to use these levels: you can specify your own and use a more general
33:class:`Logger` method, :meth:`log`, which takes an explicit level argument.
34
Georg Brandlc37f2882007-12-04 17:46:27 +000035
36Logging tutorial
37----------------
38
39The key benefit of having the logging API provided by a standard library module
40is that all Python modules can participate in logging, so your application log
41can include messages from third-party modules.
42
43It is, of course, possible to log messages with different verbosity levels or to
44different destinations. Support for writing log messages to files, HTTP
45GET/POST locations, email via SMTP, generic sockets, or OS-specific logging
Georg Brandl907a7202008-02-22 12:31:45 +000046mechanisms are all supported by the standard module. You can also create your
Georg Brandlc37f2882007-12-04 17:46:27 +000047own log destination class if you have special requirements not met by any of the
48built-in classes.
49
50Simple examples
51^^^^^^^^^^^^^^^
52
53.. sectionauthor:: Doug Hellmann
54.. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>)
55
56Most applications are probably going to want to log to a file, so let's start
57with that case. Using the :func:`basicConfig` function, we can set up the
58default handler so that debug messages are written to a file::
59
60 import logging
61 LOG_FILENAME = '/tmp/logging_example.out'
62 logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,)
63
64 logging.debug('This message should go to the log file')
65
66And now if we open the file and look at what we have, we should find the log
67message::
68
69 DEBUG:root:This message should go to the log file
70
71If you run the script repeatedly, the additional log messages are appended to
72the file. To create a new file each time, you can pass a filemode argument to
73:func:`basicConfig` with a value of ``'w'``. Rather than managing the file size
74yourself, though, it is simpler to use a :class:`RotatingFileHandler`::
75
76 import glob
77 import logging
78 import logging.handlers
79
80 LOG_FILENAME = '/tmp/logging_rotatingfile_example.out'
81
82 # Set up a specific logger with our desired output level
83 my_logger = logging.getLogger('MyLogger')
84 my_logger.setLevel(logging.DEBUG)
85
86 # Add the log message handler to the logger
87 handler = logging.handlers.RotatingFileHandler(
88 LOG_FILENAME, maxBytes=20, backupCount=5)
89
90 my_logger.addHandler(handler)
91
92 # Log some messages
93 for i in range(20):
94 my_logger.debug('i = %d' % i)
95
96 # See what files are created
97 logfiles = glob.glob('%s*' % LOG_FILENAME)
98
99 for filename in logfiles:
100 print filename
101
102The result should be 6 separate files, each with part of the log history for the
103application::
104
105 /tmp/logging_rotatingfile_example.out
106 /tmp/logging_rotatingfile_example.out.1
107 /tmp/logging_rotatingfile_example.out.2
108 /tmp/logging_rotatingfile_example.out.3
109 /tmp/logging_rotatingfile_example.out.4
110 /tmp/logging_rotatingfile_example.out.5
111
112The most current file is always :file:`/tmp/logging_rotatingfile_example.out`,
113and each time it reaches the size limit it is renamed with the suffix
114``.1``. Each of the existing backup files is renamed to increment the suffix
115(``.1`` becomes ``.2``, etc.) and the ``.5`` file is erased.
116
117Obviously this example sets the log length much much too small as an extreme
118example. You would want to set *maxBytes* to an appropriate value.
119
120Another useful feature of the logging API is the ability to produce different
121messages at different log levels. This allows you to instrument your code with
122debug messages, for example, but turning the log level down so that those debug
123messages are not written for your production system. The default levels are
124``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO``, ``DEBUG`` and ``UNSET``.
125
126The logger, handler, and log message call each specify a level. The log message
127is only emitted if the handler and logger are configured to emit messages of
128that level or lower. For example, if a message is ``CRITICAL``, and the logger
129is set to ``ERROR``, the message is emitted. If a message is a ``WARNING``, and
130the logger is set to produce only ``ERROR``\s, the message is not emitted::
131
132 import logging
133 import sys
134
135 LEVELS = {'debug': logging.DEBUG,
136 'info': logging.INFO,
137 'warning': logging.WARNING,
138 'error': logging.ERROR,
139 'critical': logging.CRITICAL}
140
141 if len(sys.argv) > 1:
142 level_name = sys.argv[1]
143 level = LEVELS.get(level_name, logging.NOTSET)
144 logging.basicConfig(level=level)
145
146 logging.debug('This is a debug message')
147 logging.info('This is an info message')
148 logging.warning('This is a warning message')
149 logging.error('This is an error message')
150 logging.critical('This is a critical error message')
151
152Run the script with an argument like 'debug' or 'warning' to see which messages
153show up at different levels::
154
155 $ python logging_level_example.py debug
156 DEBUG:root:This is a debug message
157 INFO:root:This is an info message
158 WARNING:root:This is a warning message
159 ERROR:root:This is an error message
160 CRITICAL:root:This is a critical error message
161
162 $ python logging_level_example.py info
163 INFO:root:This is an info message
164 WARNING:root:This is a warning message
165 ERROR:root:This is an error message
166 CRITICAL:root:This is a critical error message
167
168You will notice that these log messages all have ``root`` embedded in them. The
169logging module supports a hierarchy of loggers with different names. An easy
170way to tell where a specific log message comes from is to use a separate logger
171object for each of your modules. Each new logger "inherits" the configuration
172of its parent, and log messages sent to a logger include the name of that
173logger. Optionally, each logger can be configured differently, so that messages
174from different modules are handled in different ways. Let's look at a simple
175example of how to log from different modules so it is easy to trace the source
176of the message::
177
178 import logging
179
180 logging.basicConfig(level=logging.WARNING)
181
182 logger1 = logging.getLogger('package1.module1')
183 logger2 = logging.getLogger('package2.module2')
184
185 logger1.warning('This message comes from one module')
186 logger2.warning('And this message comes from another module')
187
188And the output::
189
190 $ python logging_modules_example.py
191 WARNING:package1.module1:This message comes from one module
192 WARNING:package2.module2:And this message comes from another module
193
194There are many more options for configuring logging, including different log
195message formatting options, having messages delivered to multiple destinations,
196and changing the configuration of a long-running application on the fly using a
197socket interface. All of these options are covered in depth in the library
198module documentation.
199
200Loggers
201^^^^^^^
202
203The logging library takes a modular approach and offers the several categories
204of components: loggers, handlers, filters, and formatters. Loggers expose the
205interface that application code directly uses. Handlers send the log records to
206the appropriate destination. Filters provide a finer grained facility for
207determining which log records to send on to a handler. Formatters specify the
208layout of the resultant log record.
209
210:class:`Logger` objects have a threefold job. First, they expose several
211methods to application code so that applications can log messages at runtime.
212Second, logger objects determine which log messages to act upon based upon
213severity (the default filtering facility) or filter objects. Third, logger
214objects pass along relevant log messages to all interested log handlers.
215
216The most widely used methods on logger objects fall into two categories:
217configuration and message sending.
218
219* :meth:`Logger.setLevel` specifies the lowest-severity log message a logger
220 will handle, where debug is the lowest built-in severity level and critical is
221 the highest built-in severity. For example, if the severity level is info,
222 the logger will handle only info, warning, error, and critical messages and
223 will ignore debug messages.
224
225* :meth:`Logger.addFilter` and :meth:`Logger.removeFilter` add and remove filter
226 objects from the logger object. This tutorial does not address filters.
227
228With the logger object configured, the following methods create log messages:
229
230* :meth:`Logger.debug`, :meth:`Logger.info`, :meth:`Logger.warning`,
231 :meth:`Logger.error`, and :meth:`Logger.critical` all create log records with
232 a message and a level that corresponds to their respective method names. The
233 message is actually a format string, which may contain the standard string
234 substitution syntax of :const:`%s`, :const:`%d`, :const:`%f`, and so on. The
235 rest of their arguments is a list of objects that correspond with the
236 substitution fields in the message. With regard to :const:`**kwargs`, the
237 logging methods care only about a keyword of :const:`exc_info` and use it to
238 determine whether to log exception information.
239
240* :meth:`Logger.exception` creates a log message similar to
241 :meth:`Logger.error`. The difference is that :meth:`Logger.exception` dumps a
242 stack trace along with it. Call this method only from an exception handler.
243
244* :meth:`Logger.log` takes a log level as an explicit argument. This is a
245 little more verbose for logging messages than using the log level convenience
246 methods listed above, but this is how to log at custom log levels.
247
Brett Cannon499969a2008-02-25 05:33:07 +0000248:func:`getLogger` returns a reference to a logger instance with the specified
249if it it is provided, or ``root`` if not. The names are period-separated
Georg Brandlc37f2882007-12-04 17:46:27 +0000250hierarchical structures. Multiple calls to :func:`getLogger` with the same name
251will return a reference to the same logger object. Loggers that are further
252down in the hierarchical list are children of loggers higher up in the list.
253For example, given a logger with a name of ``foo``, loggers with names of
254``foo.bar``, ``foo.bar.baz``, and ``foo.bam`` are all children of ``foo``.
255Child loggers propagate messages up to their parent loggers. Because of this,
256it is unnecessary to define and configure all the loggers an application uses.
257It is sufficient to configure a top-level logger and create child loggers as
258needed.
259
260
261Handlers
262^^^^^^^^
263
264:class:`Handler` objects are responsible for dispatching the appropriate log
265messages (based on the log messages' severity) to the handler's specified
266destination. Logger objects can add zero or more handler objects to themselves
267with an :func:`addHandler` method. As an example scenario, an application may
268want to send all log messages to a log file, all log messages of error or higher
269to stdout, and all messages of critical to an email address. This scenario
Georg Brandl907a7202008-02-22 12:31:45 +0000270requires three individual handlers where each handler is responsible for sending
Georg Brandlc37f2882007-12-04 17:46:27 +0000271messages of a specific severity to a specific location.
272
273The standard library includes quite a few handler types; this tutorial uses only
274:class:`StreamHandler` and :class:`FileHandler` in its examples.
275
276There are very few methods in a handler for application developers to concern
277themselves with. The only handler methods that seem relevant for application
278developers who are using the built-in handler objects (that is, not creating
279custom handlers) are the following configuration methods:
280
281* The :meth:`Handler.setLevel` method, just as in logger objects, specifies the
282 lowest severity that will be dispatched to the appropriate destination. Why
283 are there two :func:`setLevel` methods? The level set in the logger
284 determines which severity of messages it will pass to its handlers. The level
285 set in each handler determines which messages that handler will send on.
286 :func:`setFormatter` selects a Formatter object for this handler to use.
287
288* :func:`addFilter` and :func:`removeFilter` respectively configure and
289 deconfigure filter objects on handlers.
290
291Application code should not directly instantiate and use handlers. Instead, the
292:class:`Handler` class is a base class that defines the interface that all
293Handlers should have and establishes some default behavior that child classes
294can use (or override).
295
296
297Formatters
298^^^^^^^^^^
299
300Formatter objects configure the final order, structure, and contents of the log
Brett Cannon499969a2008-02-25 05:33:07 +0000301message. Unlike the base :class:`logging.Handler` class, application code may
Georg Brandlc37f2882007-12-04 17:46:27 +0000302instantiate formatter classes, although you could likely subclass the formatter
303if your application needs special behavior. The constructor takes two optional
304arguments: a message format string and a date format string. If there is no
305message format string, the default is to use the raw message. If there is no
306date format string, the default date format is::
307
308 %Y-%m-%d %H:%M:%S
309
310with the milliseconds tacked on at the end.
311
312The message format string uses ``%(<dictionary key>)s`` styled string
313substitution; the possible keys are documented in :ref:`formatter-objects`.
314
315The following message format string will log the time in a human-readable
316format, the severity of the message, and the contents of the message, in that
317order::
318
319 "%(asctime)s - %(levelname)s - %(message)s"
320
321
322Configuring Logging
323^^^^^^^^^^^^^^^^^^^
324
325Programmers can configure logging either by creating loggers, handlers, and
326formatters explicitly in a main module with the configuration methods listed
327above (using Python code), or by creating a logging config file. The following
328code is an example of configuring a very simple logger, a console handler, and a
329simple formatter in a Python module::
330
331 import logging
332
333 # create logger
334 logger = logging.getLogger("simple_example")
335 logger.setLevel(logging.DEBUG)
336 # create console handler and set level to debug
337 ch = logging.StreamHandler()
338 ch.setLevel(logging.DEBUG)
339 # create formatter
340 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
341 # add formatter to ch
342 ch.setFormatter(formatter)
343 # add ch to logger
344 logger.addHandler(ch)
345
346 # "application" code
347 logger.debug("debug message")
348 logger.info("info message")
349 logger.warn("warn message")
350 logger.error("error message")
351 logger.critical("critical message")
352
353Running this module from the command line produces the following output::
354
355 $ python simple_logging_module.py
356 2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message
357 2005-03-19 15:10:26,620 - simple_example - INFO - info message
358 2005-03-19 15:10:26,695 - simple_example - WARNING - warn message
359 2005-03-19 15:10:26,697 - simple_example - ERROR - error message
360 2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message
361
362The following Python module creates a logger, handler, and formatter nearly
363identical to those in the example listed above, with the only difference being
364the names of the objects::
365
366 import logging
367 import logging.config
368
369 logging.config.fileConfig("logging.conf")
370
371 # create logger
372 logger = logging.getLogger("simpleExample")
373
374 # "application" code
375 logger.debug("debug message")
376 logger.info("info message")
377 logger.warn("warn message")
378 logger.error("error message")
379 logger.critical("critical message")
380
381Here is the logging.conf file::
382
383 [loggers]
384 keys=root,simpleExample
385
386 [handlers]
387 keys=consoleHandler
388
389 [formatters]
390 keys=simpleFormatter
391
392 [logger_root]
393 level=DEBUG
394 handlers=consoleHandler
395
396 [logger_simpleExample]
397 level=DEBUG
398 handlers=consoleHandler
399 qualname=simpleExample
400 propagate=0
401
402 [handler_consoleHandler]
403 class=StreamHandler
404 level=DEBUG
405 formatter=simpleFormatter
406 args=(sys.stdout,)
407
408 [formatter_simpleFormatter]
409 format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
410 datefmt=
411
412The output is nearly identical to that of the non-config-file-based example::
413
414 $ python simple_logging_config.py
415 2005-03-19 15:38:55,977 - simpleExample - DEBUG - debug message
416 2005-03-19 15:38:55,979 - simpleExample - INFO - info message
417 2005-03-19 15:38:56,054 - simpleExample - WARNING - warn message
418 2005-03-19 15:38:56,055 - simpleExample - ERROR - error message
419 2005-03-19 15:38:56,130 - simpleExample - CRITICAL - critical message
420
421You can see that the config file approach has a few advantages over the Python
422code approach, mainly separation of configuration and code and the ability of
423noncoders to easily modify the logging properties.
424
425
426Logging Levels
427--------------
428
Georg Brandl8ec7f652007-08-15 14:28:01 +0000429The numeric values of logging levels are given in the following table. These are
430primarily of interest if you want to define your own levels, and need them to
431have specific values relative to the predefined levels. If you define a level
432with the same numeric value, it overwrites the predefined value; the predefined
433name is lost.
434
435+--------------+---------------+
436| Level | Numeric value |
437+==============+===============+
438| ``CRITICAL`` | 50 |
439+--------------+---------------+
440| ``ERROR`` | 40 |
441+--------------+---------------+
442| ``WARNING`` | 30 |
443+--------------+---------------+
444| ``INFO`` | 20 |
445+--------------+---------------+
446| ``DEBUG`` | 10 |
447+--------------+---------------+
448| ``NOTSET`` | 0 |
449+--------------+---------------+
450
451Levels can also be associated with loggers, being set either by the developer or
452through loading a saved logging configuration. When a logging method is called
453on a logger, the logger compares its own level with the level associated with
454the method call. If the logger's level is higher than the method call's, no
455logging message is actually generated. This is the basic mechanism controlling
456the verbosity of logging output.
457
458Logging messages are encoded as instances of the :class:`LogRecord` class. When
459a logger decides to actually log an event, a :class:`LogRecord` instance is
460created from the logging message.
461
462Logging messages are subjected to a dispatch mechanism through the use of
463:dfn:`handlers`, which are instances of subclasses of the :class:`Handler`
464class. Handlers are responsible for ensuring that a logged message (in the form
465of a :class:`LogRecord`) ends up in a particular location (or set of locations)
466which is useful for the target audience for that message (such as end users,
467support desk staff, system administrators, developers). Handlers are passed
468:class:`LogRecord` instances intended for particular destinations. Each logger
469can have zero, one or more handlers associated with it (via the
470:meth:`addHandler` method of :class:`Logger`). In addition to any handlers
471directly associated with a logger, *all handlers associated with all ancestors
472of the logger* are called to dispatch the message.
473
474Just as for loggers, handlers can have levels associated with them. A handler's
475level acts as a filter in the same way as a logger's level does. If a handler
476decides to actually dispatch an event, the :meth:`emit` method is used to send
477the message to its destination. Most user-defined subclasses of :class:`Handler`
478will need to override this :meth:`emit`.
479
480In addition to the base :class:`Handler` class, many useful subclasses are
481provided:
482
483#. :class:`StreamHandler` instances send error messages to streams (file-like
484 objects).
485
486#. :class:`FileHandler` instances send error messages to disk files.
487
488#. :class:`BaseRotatingHandler` is the base class for handlers that rotate log
489 files at a certain point. It is not meant to be instantiated directly. Instead,
490 use :class:`RotatingFileHandler` or :class:`TimedRotatingFileHandler`.
491
492#. :class:`RotatingFileHandler` instances send error messages to disk files,
493 with support for maximum log file sizes and log file rotation.
494
495#. :class:`TimedRotatingFileHandler` instances send error messages to disk files
496 rotating the log file at certain timed intervals.
497
498#. :class:`SocketHandler` instances send error messages to TCP/IP sockets.
499
500#. :class:`DatagramHandler` instances send error messages to UDP sockets.
501
502#. :class:`SMTPHandler` instances send error messages to a designated email
503 address.
504
505#. :class:`SysLogHandler` instances send error messages to a Unix syslog daemon,
506 possibly on a remote machine.
507
508#. :class:`NTEventLogHandler` instances send error messages to a Windows
509 NT/2000/XP event log.
510
511#. :class:`MemoryHandler` instances send error messages to a buffer in memory,
512 which is flushed whenever specific criteria are met.
513
514#. :class:`HTTPHandler` instances send error messages to an HTTP server using
515 either ``GET`` or ``POST`` semantics.
516
517The :class:`StreamHandler` and :class:`FileHandler` classes are defined in the
518core logging package. The other handlers are defined in a sub- module,
519:mod:`logging.handlers`. (There is also another sub-module,
520:mod:`logging.config`, for configuration functionality.)
521
522Logged messages are formatted for presentation through instances of the
523:class:`Formatter` class. They are initialized with a format string suitable for
524use with the % operator and a dictionary.
525
526For formatting multiple messages in a batch, instances of
527:class:`BufferingFormatter` can be used. In addition to the format string (which
528is applied to each message in the batch), there is provision for header and
529trailer format strings.
530
531When filtering based on logger level and/or handler level is not enough,
532instances of :class:`Filter` can be added to both :class:`Logger` and
533:class:`Handler` instances (through their :meth:`addFilter` method). Before
534deciding to process a message further, both loggers and handlers consult all
535their filters for permission. If any filter returns a false value, the message
536is not processed further.
537
538The basic :class:`Filter` functionality allows filtering by specific logger
539name. If this feature is used, messages sent to the named logger and its
540children are allowed through the filter, and all others dropped.
541
542In addition to the classes described above, there are a number of module- level
543functions.
544
545
546.. function:: getLogger([name])
547
548 Return a logger with the specified name or, if no name is specified, return a
549 logger which is the root logger of the hierarchy. If specified, the name is
550 typically a dot-separated hierarchical name like *"a"*, *"a.b"* or *"a.b.c.d"*.
551 Choice of these names is entirely up to the developer who is using logging.
552
553 All calls to this function with a given name return the same logger instance.
554 This means that logger instances never need to be passed between different parts
555 of an application.
556
557
558.. function:: getLoggerClass()
559
560 Return either the standard :class:`Logger` class, or the last class passed to
561 :func:`setLoggerClass`. This function may be called from within a new class
562 definition, to ensure that installing a customised :class:`Logger` class will
563 not undo customisations already applied by other code. For example::
564
565 class MyLogger(logging.getLoggerClass()):
566 # ... override behaviour here
567
568
569.. function:: debug(msg[, *args[, **kwargs]])
570
571 Logs a message with level :const:`DEBUG` on the root logger. The *msg* is the
572 message format string, and the *args* are the arguments which are merged into
573 *msg* using the string formatting operator. (Note that this means that you can
574 use keywords in the format string, together with a single dictionary argument.)
575
576 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
577 which, if it does not evaluate as false, causes exception information to be
578 added to the logging message. If an exception tuple (in the format returned by
579 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
580 is called to get the exception information.
581
582 The other optional keyword argument is *extra* which can be used to pass a
583 dictionary which is used to populate the __dict__ of the LogRecord created for
584 the logging event with user-defined attributes. These custom attributes can then
585 be used as you like. For example, they could be incorporated into logged
586 messages. For example::
587
588 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
589 logging.basicConfig(format=FORMAT)
590 d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
591 logging.warning("Protocol problem: %s", "connection reset", extra=d)
592
593 would print something like ::
594
595 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
596
597 The keys in the dictionary passed in *extra* should not clash with the keys used
598 by the logging system. (See the :class:`Formatter` documentation for more
599 information on which keys are used by the logging system.)
600
601 If you choose to use these attributes in logged messages, you need to exercise
602 some care. In the above example, for instance, the :class:`Formatter` has been
603 set up with a format string which expects 'clientip' and 'user' in the attribute
604 dictionary of the LogRecord. If these are missing, the message will not be
605 logged because a string formatting exception will occur. So in this case, you
606 always need to pass the *extra* dictionary with these keys.
607
608 While this might be annoying, this feature is intended for use in specialized
609 circumstances, such as multi-threaded servers where the same code executes in
610 many contexts, and interesting conditions which arise are dependent on this
611 context (such as remote client IP address and authenticated user name, in the
612 above example). In such circumstances, it is likely that specialized
613 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
614
615 .. versionchanged:: 2.5
616 *extra* was added.
617
618
619.. function:: info(msg[, *args[, **kwargs]])
620
621 Logs a message with level :const:`INFO` on the root logger. The arguments are
622 interpreted as for :func:`debug`.
623
624
625.. function:: warning(msg[, *args[, **kwargs]])
626
627 Logs a message with level :const:`WARNING` on the root logger. The arguments are
628 interpreted as for :func:`debug`.
629
630
631.. function:: error(msg[, *args[, **kwargs]])
632
633 Logs a message with level :const:`ERROR` on the root logger. The arguments are
634 interpreted as for :func:`debug`.
635
636
637.. function:: critical(msg[, *args[, **kwargs]])
638
639 Logs a message with level :const:`CRITICAL` on the root logger. The arguments
640 are interpreted as for :func:`debug`.
641
642
643.. function:: exception(msg[, *args])
644
645 Logs a message with level :const:`ERROR` on the root logger. The arguments are
646 interpreted as for :func:`debug`. Exception info is added to the logging
647 message. This function should only be called from an exception handler.
648
649
650.. function:: log(level, msg[, *args[, **kwargs]])
651
652 Logs a message with level *level* on the root logger. The other arguments are
653 interpreted as for :func:`debug`.
654
655
656.. function:: disable(lvl)
657
658 Provides an overriding level *lvl* for all loggers which takes precedence over
659 the logger's own level. When the need arises to temporarily throttle logging
660 output down across the whole application, this function can be useful.
661
662
663.. function:: addLevelName(lvl, levelName)
664
665 Associates level *lvl* with text *levelName* in an internal dictionary, which is
666 used to map numeric levels to a textual representation, for example when a
667 :class:`Formatter` formats a message. This function can also be used to define
668 your own levels. The only constraints are that all levels used must be
669 registered using this function, levels should be positive integers and they
670 should increase in increasing order of severity.
671
672
673.. function:: getLevelName(lvl)
674
675 Returns the textual representation of logging level *lvl*. If the level is one
676 of the predefined levels :const:`CRITICAL`, :const:`ERROR`, :const:`WARNING`,
677 :const:`INFO` or :const:`DEBUG` then you get the corresponding string. If you
678 have associated levels with names using :func:`addLevelName` then the name you
679 have associated with *lvl* is returned. If a numeric value corresponding to one
680 of the defined levels is passed in, the corresponding string representation is
681 returned. Otherwise, the string "Level %s" % lvl is returned.
682
683
684.. function:: makeLogRecord(attrdict)
685
686 Creates and returns a new :class:`LogRecord` instance whose attributes are
687 defined by *attrdict*. This function is useful for taking a pickled
688 :class:`LogRecord` attribute dictionary, sent over a socket, and reconstituting
689 it as a :class:`LogRecord` instance at the receiving end.
690
691
692.. function:: basicConfig([**kwargs])
693
694 Does basic configuration for the logging system by creating a
695 :class:`StreamHandler` with a default :class:`Formatter` and adding it to the
Vinay Sajipe28fa292008-01-07 15:30:36 +0000696 root logger. The function does nothing if any handlers have been defined for
697 the root logger. The functions :func:`debug`, :func:`info`, :func:`warning`,
Georg Brandl8ec7f652007-08-15 14:28:01 +0000698 :func:`error` and :func:`critical` will call :func:`basicConfig` automatically
699 if no handlers are defined for the root logger.
700
701 .. versionchanged:: 2.4
702 Formerly, :func:`basicConfig` did not take any keyword arguments.
703
704 The following keyword arguments are supported.
705
706 +--------------+---------------------------------------------+
707 | Format | Description |
708 +==============+=============================================+
709 | ``filename`` | Specifies that a FileHandler be created, |
710 | | using the specified filename, rather than a |
711 | | StreamHandler. |
712 +--------------+---------------------------------------------+
713 | ``filemode`` | Specifies the mode to open the file, if |
714 | | filename is specified (if filemode is |
715 | | unspecified, it defaults to 'a'). |
716 +--------------+---------------------------------------------+
717 | ``format`` | Use the specified format string for the |
718 | | handler. |
719 +--------------+---------------------------------------------+
720 | ``datefmt`` | Use the specified date/time format. |
721 +--------------+---------------------------------------------+
722 | ``level`` | Set the root logger level to the specified |
723 | | level. |
724 +--------------+---------------------------------------------+
725 | ``stream`` | Use the specified stream to initialize the |
726 | | StreamHandler. Note that this argument is |
727 | | incompatible with 'filename' - if both are |
728 | | present, 'stream' is ignored. |
729 +--------------+---------------------------------------------+
730
731
732.. function:: shutdown()
733
734 Informs the logging system to perform an orderly shutdown by flushing and
Vinay Sajip91f0ee42008-03-16 21:35:58 +0000735 closing all handlers. This should be called at application exit and no
736 further use of the logging system should be made after this call.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000737
738
739.. function:: setLoggerClass(klass)
740
741 Tells the logging system to use the class *klass* when instantiating a logger.
742 The class should define :meth:`__init__` such that only a name argument is
743 required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
744 function is typically called before any loggers are instantiated by applications
745 which need to use custom logger behavior.
746
747
748.. seealso::
749
750 :pep:`282` - A Logging System
751 The proposal which described this feature for inclusion in the Python standard
752 library.
753
Georg Brandl2b92f6b2007-12-06 01:52:24 +0000754 `Original Python logging package <http://www.red-dove.com/python_logging.html>`_
Georg Brandl8ec7f652007-08-15 14:28:01 +0000755 This is the original source for the :mod:`logging` package. The version of the
756 package available from this site is suitable for use with Python 1.5.2, 2.1.x
757 and 2.2.x, which do not include the :mod:`logging` package in the standard
758 library.
759
760
761Logger Objects
762--------------
763
764Loggers have the following attributes and methods. Note that Loggers are never
765instantiated directly, but always through the module-level function
766``logging.getLogger(name)``.
767
768
769.. attribute:: Logger.propagate
770
771 If this evaluates to false, logging messages are not passed by this logger or by
772 child loggers to higher level (ancestor) loggers. The constructor sets this
773 attribute to 1.
774
775
776.. method:: Logger.setLevel(lvl)
777
778 Sets the threshold for this logger to *lvl*. Logging messages which are less
779 severe than *lvl* will be ignored. When a logger is created, the level is set to
780 :const:`NOTSET` (which causes all messages to be processed when the logger is
781 the root logger, or delegation to the parent when the logger is a non-root
782 logger). Note that the root logger is created with level :const:`WARNING`.
783
784 The term "delegation to the parent" means that if a logger has a level of
785 NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
786 a level other than NOTSET is found, or the root is reached.
787
788 If an ancestor is found with a level other than NOTSET, then that ancestor's
789 level is treated as the effective level of the logger where the ancestor search
790 began, and is used to determine how a logging event is handled.
791
792 If the root is reached, and it has a level of NOTSET, then all messages will be
793 processed. Otherwise, the root's level will be used as the effective level.
794
795
796.. method:: Logger.isEnabledFor(lvl)
797
798 Indicates if a message of severity *lvl* would be processed by this logger.
799 This method checks first the module-level level set by
800 ``logging.disable(lvl)`` and then the logger's effective level as determined
801 by :meth:`getEffectiveLevel`.
802
803
804.. method:: Logger.getEffectiveLevel()
805
806 Indicates the effective level for this logger. If a value other than
807 :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
808 the hierarchy is traversed towards the root until a value other than
809 :const:`NOTSET` is found, and that value is returned.
810
811
812.. method:: Logger.debug(msg[, *args[, **kwargs]])
813
814 Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
815 message format string, and the *args* are the arguments which are merged into
816 *msg* using the string formatting operator. (Note that this means that you can
817 use keywords in the format string, together with a single dictionary argument.)
818
819 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
820 which, if it does not evaluate as false, causes exception information to be
821 added to the logging message. If an exception tuple (in the format returned by
822 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
823 is called to get the exception information.
824
825 The other optional keyword argument is *extra* which can be used to pass a
826 dictionary which is used to populate the __dict__ of the LogRecord created for
827 the logging event with user-defined attributes. These custom attributes can then
828 be used as you like. For example, they could be incorporated into logged
829 messages. For example::
830
831 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
832 logging.basicConfig(format=FORMAT)
Neal Norwitz53004282007-10-23 05:44:27 +0000833 d = { 'clientip' : '192.168.0.1', 'user' : 'fbloggs' }
Georg Brandl8ec7f652007-08-15 14:28:01 +0000834 logger = logging.getLogger("tcpserver")
835 logger.warning("Protocol problem: %s", "connection reset", extra=d)
836
837 would print something like ::
838
839 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
840
841 The keys in the dictionary passed in *extra* should not clash with the keys used
842 by the logging system. (See the :class:`Formatter` documentation for more
843 information on which keys are used by the logging system.)
844
845 If you choose to use these attributes in logged messages, you need to exercise
846 some care. In the above example, for instance, the :class:`Formatter` has been
847 set up with a format string which expects 'clientip' and 'user' in the attribute
848 dictionary of the LogRecord. If these are missing, the message will not be
849 logged because a string formatting exception will occur. So in this case, you
850 always need to pass the *extra* dictionary with these keys.
851
852 While this might be annoying, this feature is intended for use in specialized
853 circumstances, such as multi-threaded servers where the same code executes in
854 many contexts, and interesting conditions which arise are dependent on this
855 context (such as remote client IP address and authenticated user name, in the
856 above example). In such circumstances, it is likely that specialized
857 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
858
859 .. versionchanged:: 2.5
860 *extra* was added.
861
862
863.. method:: Logger.info(msg[, *args[, **kwargs]])
864
865 Logs a message with level :const:`INFO` on this logger. The arguments are
866 interpreted as for :meth:`debug`.
867
868
869.. method:: Logger.warning(msg[, *args[, **kwargs]])
870
871 Logs a message with level :const:`WARNING` on this logger. The arguments are
872 interpreted as for :meth:`debug`.
873
874
875.. method:: Logger.error(msg[, *args[, **kwargs]])
876
877 Logs a message with level :const:`ERROR` on this logger. The arguments are
878 interpreted as for :meth:`debug`.
879
880
881.. method:: Logger.critical(msg[, *args[, **kwargs]])
882
883 Logs a message with level :const:`CRITICAL` on this logger. The arguments are
884 interpreted as for :meth:`debug`.
885
886
887.. method:: Logger.log(lvl, msg[, *args[, **kwargs]])
888
889 Logs a message with integer level *lvl* on this logger. The other arguments are
890 interpreted as for :meth:`debug`.
891
892
893.. method:: Logger.exception(msg[, *args])
894
895 Logs a message with level :const:`ERROR` on this logger. The arguments are
896 interpreted as for :meth:`debug`. Exception info is added to the logging
897 message. This method should only be called from an exception handler.
898
899
900.. method:: Logger.addFilter(filt)
901
902 Adds the specified filter *filt* to this logger.
903
904
905.. method:: Logger.removeFilter(filt)
906
907 Removes the specified filter *filt* from this logger.
908
909
910.. method:: Logger.filter(record)
911
912 Applies this logger's filters to the record and returns a true value if the
913 record is to be processed.
914
915
916.. method:: Logger.addHandler(hdlr)
917
918 Adds the specified handler *hdlr* to this logger.
919
920
921.. method:: Logger.removeHandler(hdlr)
922
923 Removes the specified handler *hdlr* from this logger.
924
925
926.. method:: Logger.findCaller()
927
928 Finds the caller's source filename and line number. Returns the filename, line
929 number and function name as a 3-element tuple.
930
Matthias Klosef0e29182007-08-16 12:03:44 +0000931 .. versionchanged:: 2.4
Georg Brandl8ec7f652007-08-15 14:28:01 +0000932 The function name was added. In earlier versions, the filename and line number
933 were returned as a 2-element tuple..
934
935
936.. method:: Logger.handle(record)
937
938 Handles a record by passing it to all handlers associated with this logger and
939 its ancestors (until a false value of *propagate* is found). This method is used
940 for unpickled records received from a socket, as well as those created locally.
941 Logger-level filtering is applied using :meth:`filter`.
942
943
944.. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info [, func, extra])
945
946 This is a factory method which can be overridden in subclasses to create
947 specialized :class:`LogRecord` instances.
948
949 .. versionchanged:: 2.5
950 *func* and *extra* were added.
951
952
953.. _minimal-example:
954
955Basic example
956-------------
957
958.. versionchanged:: 2.4
959 formerly :func:`basicConfig` did not take any keyword arguments.
960
961The :mod:`logging` package provides a lot of flexibility, and its configuration
962can appear daunting. This section demonstrates that simple use of the logging
963package is possible.
964
965The simplest example shows logging to the console::
966
967 import logging
968
969 logging.debug('A debug message')
970 logging.info('Some information')
971 logging.warning('A shot across the bows')
972
973If you run the above script, you'll see this::
974
975 WARNING:root:A shot across the bows
976
977Because no particular logger was specified, the system used the root logger. The
978debug and info messages didn't appear because by default, the root logger is
979configured to only handle messages with a severity of WARNING or above. The
980message format is also a configuration default, as is the output destination of
981the messages - ``sys.stderr``. The severity level, the message format and
982destination can be easily changed, as shown in the example below::
983
984 import logging
985
986 logging.basicConfig(level=logging.DEBUG,
987 format='%(asctime)s %(levelname)s %(message)s',
988 filename='/tmp/myapp.log',
989 filemode='w')
990 logging.debug('A debug message')
991 logging.info('Some information')
992 logging.warning('A shot across the bows')
993
994The :meth:`basicConfig` method is used to change the configuration defaults,
995which results in output (written to ``/tmp/myapp.log``) which should look
996something like the following::
997
998 2004-07-02 13:00:08,743 DEBUG A debug message
999 2004-07-02 13:00:08,743 INFO Some information
1000 2004-07-02 13:00:08,743 WARNING A shot across the bows
1001
1002This time, all messages with a severity of DEBUG or above were handled, and the
1003format of the messages was also changed, and output went to the specified file
1004rather than the console.
1005
1006Formatting uses standard Python string formatting - see section
1007:ref:`string-formatting`. The format string takes the following common
1008specifiers. For a complete list of specifiers, consult the :class:`Formatter`
1009documentation.
1010
1011+-------------------+-----------------------------------------------+
1012| Format | Description |
1013+===================+===============================================+
1014| ``%(name)s`` | Name of the logger (logging channel). |
1015+-------------------+-----------------------------------------------+
1016| ``%(levelname)s`` | Text logging level for the message |
1017| | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1018| | ``'ERROR'``, ``'CRITICAL'``). |
1019+-------------------+-----------------------------------------------+
1020| ``%(asctime)s`` | Human-readable time when the |
1021| | :class:`LogRecord` was created. By default |
1022| | this is of the form "2003-07-08 16:49:45,896" |
1023| | (the numbers after the comma are millisecond |
1024| | portion of the time). |
1025+-------------------+-----------------------------------------------+
1026| ``%(message)s`` | The logged message. |
1027+-------------------+-----------------------------------------------+
1028
1029To change the date/time format, you can pass an additional keyword parameter,
1030*datefmt*, as in the following::
1031
1032 import logging
1033
1034 logging.basicConfig(level=logging.DEBUG,
1035 format='%(asctime)s %(levelname)-8s %(message)s',
1036 datefmt='%a, %d %b %Y %H:%M:%S',
1037 filename='/temp/myapp.log',
1038 filemode='w')
1039 logging.debug('A debug message')
1040 logging.info('Some information')
1041 logging.warning('A shot across the bows')
1042
1043which would result in output like ::
1044
1045 Fri, 02 Jul 2004 13:06:18 DEBUG A debug message
1046 Fri, 02 Jul 2004 13:06:18 INFO Some information
1047 Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows
1048
1049The date format string follows the requirements of :func:`strftime` - see the
1050documentation for the :mod:`time` module.
1051
1052If, instead of sending logging output to the console or a file, you'd rather use
1053a file-like object which you have created separately, you can pass it to
1054:func:`basicConfig` using the *stream* keyword argument. Note that if both
1055*stream* and *filename* keyword arguments are passed, the *stream* argument is
1056ignored.
1057
1058Of course, you can put variable information in your output. To do this, simply
1059have the message be a format string and pass in additional arguments containing
1060the variable information, as in the following example::
1061
1062 import logging
1063
1064 logging.basicConfig(level=logging.DEBUG,
1065 format='%(asctime)s %(levelname)-8s %(message)s',
1066 datefmt='%a, %d %b %Y %H:%M:%S',
1067 filename='/temp/myapp.log',
1068 filemode='w')
1069 logging.error('Pack my box with %d dozen %s', 5, 'liquor jugs')
1070
1071which would result in ::
1072
1073 Wed, 21 Jul 2004 15:35:16 ERROR Pack my box with 5 dozen liquor jugs
1074
1075
1076.. _multiple-destinations:
1077
1078Logging to multiple destinations
1079--------------------------------
1080
1081Let's say you want to log to console and file with different message formats and
1082in differing circumstances. Say you want to log messages with levels of DEBUG
1083and higher to file, and those messages at level INFO and higher to the console.
1084Let's also assume that the file should contain timestamps, but the console
1085messages should not. Here's how you can achieve this::
1086
1087 import logging
1088
1089 # set up logging to file - see previous section for more details
1090 logging.basicConfig(level=logging.DEBUG,
1091 format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
1092 datefmt='%m-%d %H:%M',
1093 filename='/temp/myapp.log',
1094 filemode='w')
1095 # define a Handler which writes INFO messages or higher to the sys.stderr
1096 console = logging.StreamHandler()
1097 console.setLevel(logging.INFO)
1098 # set a format which is simpler for console use
1099 formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
1100 # tell the handler to use this format
1101 console.setFormatter(formatter)
1102 # add the handler to the root logger
1103 logging.getLogger('').addHandler(console)
1104
1105 # Now, we can log to the root logger, or any other logger. First the root...
1106 logging.info('Jackdaws love my big sphinx of quartz.')
1107
1108 # Now, define a couple of other loggers which might represent areas in your
1109 # application:
1110
1111 logger1 = logging.getLogger('myapp.area1')
1112 logger2 = logging.getLogger('myapp.area2')
1113
1114 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1115 logger1.info('How quickly daft jumping zebras vex.')
1116 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1117 logger2.error('The five boxing wizards jump quickly.')
1118
1119When you run this, on the console you will see ::
1120
1121 root : INFO Jackdaws love my big sphinx of quartz.
1122 myapp.area1 : INFO How quickly daft jumping zebras vex.
1123 myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
1124 myapp.area2 : ERROR The five boxing wizards jump quickly.
1125
1126and in the file you will see something like ::
1127
1128 10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
1129 10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1130 10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
1131 10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1132 10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
1133
1134As you can see, the DEBUG message only shows up in the file. The other messages
1135are sent to both destinations.
1136
1137This example uses console and file handlers, but you can use any number and
1138combination of handlers you choose.
1139
1140
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001141.. _context-info:
1142
1143Adding contextual information to your logging output
1144----------------------------------------------------
1145
1146Sometimes you want logging output to contain contextual information in
1147addition to the parameters passed to the logging call. For example, in a
1148networked application, it may be desirable to log client-specific information
1149in the log (e.g. remote client's username, or IP address). Although you could
1150use the *extra* parameter to achieve this, it's not always convenient to pass
1151the information in this way. While it might be tempting to create
1152:class:`Logger` instances on a per-connection basis, this is not a good idea
1153because these instances are not garbage collected. While this is not a problem
1154in practice, when the number of :class:`Logger` instances is dependent on the
1155level of granularity you want to use in logging an application, it could
1156be hard to manage if the number of :class:`Logger` instances becomes
1157effectively unbounded.
1158
Vinay Sajipc7403352008-01-18 15:54:14 +00001159An easy way in which you can pass contextual information to be output along
1160with logging event information is to use the :class:`LoggerAdapter` class.
1161This class is designed to look like a :class:`Logger`, so that you can call
1162:meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
1163:meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
1164same signatures as their counterparts in :class:`Logger`, so you can use the
1165two types of instances interchangeably.
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001166
Vinay Sajipc7403352008-01-18 15:54:14 +00001167When you create an instance of :class:`LoggerAdapter`, you pass it a
1168:class:`Logger` instance and a dict-like object which contains your contextual
1169information. When you call one of the logging methods on an instance of
1170:class:`LoggerAdapter`, it delegates the call to the underlying instance of
1171:class:`Logger` passed to its constructor, and arranges to pass the contextual
1172information in the delegated call. Here's a snippet from the code of
1173:class:`LoggerAdapter`::
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001174
Vinay Sajipc7403352008-01-18 15:54:14 +00001175 def debug(self, msg, *args, **kwargs):
1176 """
1177 Delegate a debug call to the underlying logger, after adding
1178 contextual information from this adapter instance.
1179 """
1180 msg, kwargs = self.process(msg, kwargs)
1181 self.logger.debug(msg, *args, **kwargs)
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001182
Vinay Sajipc7403352008-01-18 15:54:14 +00001183The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
1184information is added to the logging output. It's passed the message and
1185keyword arguments of the logging call, and it passes back (potentially)
1186modified versions of these to use in the call to the underlying logger. The
1187default implementation of this method leaves the message alone, but inserts
1188an "extra" key in the keyword argument whose value is the dict-like object
1189passed to the constructor. Of course, if you had passed an "extra" keyword
1190argument in the call to the adapter, it will be silently overwritten.
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001191
Vinay Sajipc7403352008-01-18 15:54:14 +00001192The advantage of using "extra" is that the values in the dict-like object are
1193merged into the :class:`LogRecord` instance's __dict__, allowing you to use
1194customized strings with your :class:`Formatter` instances which know about
1195the keys of the dict-like object. If you need a different method, e.g. if you
1196want to prepend or append the contextual information to the message string,
1197you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
1198to do what you need. Here's an example script which uses this class, which
1199also illustrates what dict-like behaviour is needed from an arbitrary
1200"dict-like" object for use in the constructor::
1201
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001202 import logging
Vinay Sajip733024a2008-01-21 17:39:22 +00001203
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001204 class ConnInfo:
1205 """
1206 An example class which shows how an arbitrary class can be used as
1207 the 'extra' context information repository passed to a LoggerAdapter.
1208 """
Vinay Sajip733024a2008-01-21 17:39:22 +00001209
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001210 def __getitem__(self, name):
1211 """
1212 To allow this instance to look like a dict.
1213 """
1214 from random import choice
1215 if name == "ip":
1216 result = choice(["127.0.0.1", "192.168.0.1"])
1217 elif name == "user":
1218 result = choice(["jim", "fred", "sheila"])
1219 else:
1220 result = self.__dict__.get(name, "?")
1221 return result
Vinay Sajip733024a2008-01-21 17:39:22 +00001222
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001223 def __iter__(self):
1224 """
1225 To allow iteration over keys, which will be merged into
1226 the LogRecord dict before formatting and output.
1227 """
1228 keys = ["ip", "user"]
1229 keys.extend(self.__dict__.keys())
1230 return keys.__iter__()
Vinay Sajip733024a2008-01-21 17:39:22 +00001231
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001232 if __name__ == "__main__":
1233 from random import choice
1234 levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
1235 a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"),
1236 { "ip" : "123.231.231.123", "user" : "sheila" })
1237 logging.basicConfig(level=logging.DEBUG,
1238 format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s")
1239 a1.debug("A debug message")
1240 a1.info("An info message with %s", "some parameters")
1241 a2 = logging.LoggerAdapter(logging.getLogger("d.e.f"), ConnInfo())
1242 for x in range(10):
1243 lvl = choice(levels)
1244 lvlname = logging.getLevelName(lvl)
1245 a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters")
Vinay Sajipc7403352008-01-18 15:54:14 +00001246
1247When this script is run, the output should look something like this::
1248
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001249 2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
1250 2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
1251 2008-01-18 14:49:54,023 d.e.f CRITICAL IP: 192.168.0.1 User: jim A message at CRITICAL level with 2 parameters
1252 2008-01-18 14:49:54,033 d.e.f INFO IP: 192.168.0.1 User: jim A message at INFO level with 2 parameters
1253 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1254 2008-01-18 14:49:54,033 d.e.f ERROR IP: 127.0.0.1 User: fred A message at ERROR level with 2 parameters
1255 2008-01-18 14:49:54,033 d.e.f ERROR IP: 127.0.0.1 User: sheila A message at ERROR level with 2 parameters
1256 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1257 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: jim A message at WARNING level with 2 parameters
1258 2008-01-18 14:49:54,033 d.e.f INFO IP: 192.168.0.1 User: fred A message at INFO level with 2 parameters
1259 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1260 2008-01-18 14:49:54,033 d.e.f WARNING IP: 127.0.0.1 User: jim A message at WARNING level with 2 parameters
Vinay Sajipc7403352008-01-18 15:54:14 +00001261
1262.. versionadded:: 2.6
1263
1264The :class:`LoggerAdapter` class was not present in previous versions.
1265
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001266
Georg Brandl8ec7f652007-08-15 14:28:01 +00001267.. _network-logging:
1268
1269Sending and receiving logging events across a network
1270-----------------------------------------------------
1271
1272Let's say you want to send logging events across a network, and handle them at
1273the receiving end. A simple way of doing this is attaching a
1274:class:`SocketHandler` instance to the root logger at the sending end::
1275
1276 import logging, logging.handlers
1277
1278 rootLogger = logging.getLogger('')
1279 rootLogger.setLevel(logging.DEBUG)
1280 socketHandler = logging.handlers.SocketHandler('localhost',
1281 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1282 # don't bother with a formatter, since a socket handler sends the event as
1283 # an unformatted pickle
1284 rootLogger.addHandler(socketHandler)
1285
1286 # Now, we can log to the root logger, or any other logger. First the root...
1287 logging.info('Jackdaws love my big sphinx of quartz.')
1288
1289 # Now, define a couple of other loggers which might represent areas in your
1290 # application:
1291
1292 logger1 = logging.getLogger('myapp.area1')
1293 logger2 = logging.getLogger('myapp.area2')
1294
1295 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1296 logger1.info('How quickly daft jumping zebras vex.')
1297 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1298 logger2.error('The five boxing wizards jump quickly.')
1299
1300At the receiving end, you can set up a receiver using the :mod:`SocketServer`
1301module. Here is a basic working example::
1302
1303 import cPickle
1304 import logging
1305 import logging.handlers
1306 import SocketServer
1307 import struct
1308
1309
1310 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
1311 """Handler for a streaming logging request.
1312
1313 This basically logs the record using whatever logging policy is
1314 configured locally.
1315 """
1316
1317 def handle(self):
1318 """
1319 Handle multiple requests - each expected to be a 4-byte length,
1320 followed by the LogRecord in pickle format. Logs the record
1321 according to whatever policy is configured locally.
1322 """
1323 while 1:
1324 chunk = self.connection.recv(4)
1325 if len(chunk) < 4:
1326 break
1327 slen = struct.unpack(">L", chunk)[0]
1328 chunk = self.connection.recv(slen)
1329 while len(chunk) < slen:
1330 chunk = chunk + self.connection.recv(slen - len(chunk))
1331 obj = self.unPickle(chunk)
1332 record = logging.makeLogRecord(obj)
1333 self.handleLogRecord(record)
1334
1335 def unPickle(self, data):
1336 return cPickle.loads(data)
1337
1338 def handleLogRecord(self, record):
1339 # if a name is specified, we use the named logger rather than the one
1340 # implied by the record.
1341 if self.server.logname is not None:
1342 name = self.server.logname
1343 else:
1344 name = record.name
1345 logger = logging.getLogger(name)
1346 # N.B. EVERY record gets logged. This is because Logger.handle
1347 # is normally called AFTER logger-level filtering. If you want
1348 # to do filtering, do it at the client end to save wasting
1349 # cycles and network bandwidth!
1350 logger.handle(record)
1351
1352 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
1353 """simple TCP socket-based logging receiver suitable for testing.
1354 """
1355
1356 allow_reuse_address = 1
1357
1358 def __init__(self, host='localhost',
1359 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1360 handler=LogRecordStreamHandler):
1361 SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
1362 self.abort = 0
1363 self.timeout = 1
1364 self.logname = None
1365
1366 def serve_until_stopped(self):
1367 import select
1368 abort = 0
1369 while not abort:
1370 rd, wr, ex = select.select([self.socket.fileno()],
1371 [], [],
1372 self.timeout)
1373 if rd:
1374 self.handle_request()
1375 abort = self.abort
1376
1377 def main():
1378 logging.basicConfig(
1379 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1380 tcpserver = LogRecordSocketReceiver()
1381 print "About to start TCP server..."
1382 tcpserver.serve_until_stopped()
1383
1384 if __name__ == "__main__":
1385 main()
1386
1387First run the server, and then the client. On the client side, nothing is
1388printed on the console; on the server side, you should see something like::
1389
1390 About to start TCP server...
1391 59 root INFO Jackdaws love my big sphinx of quartz.
1392 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1393 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1394 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1395 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1396
1397
1398Handler Objects
1399---------------
1400
1401Handlers have the following attributes and methods. Note that :class:`Handler`
1402is never instantiated directly; this class acts as a base for more useful
1403subclasses. However, the :meth:`__init__` method in subclasses needs to call
1404:meth:`Handler.__init__`.
1405
1406
1407.. method:: Handler.__init__(level=NOTSET)
1408
1409 Initializes the :class:`Handler` instance by setting its level, setting the list
1410 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1411 serializing access to an I/O mechanism.
1412
1413
1414.. method:: Handler.createLock()
1415
1416 Initializes a thread lock which can be used to serialize access to underlying
1417 I/O functionality which may not be threadsafe.
1418
1419
1420.. method:: Handler.acquire()
1421
1422 Acquires the thread lock created with :meth:`createLock`.
1423
1424
1425.. method:: Handler.release()
1426
1427 Releases the thread lock acquired with :meth:`acquire`.
1428
1429
1430.. method:: Handler.setLevel(lvl)
1431
1432 Sets the threshold for this handler to *lvl*. Logging messages which are less
1433 severe than *lvl* will be ignored. When a handler is created, the level is set
1434 to :const:`NOTSET` (which causes all messages to be processed).
1435
1436
1437.. method:: Handler.setFormatter(form)
1438
1439 Sets the :class:`Formatter` for this handler to *form*.
1440
1441
1442.. method:: Handler.addFilter(filt)
1443
1444 Adds the specified filter *filt* to this handler.
1445
1446
1447.. method:: Handler.removeFilter(filt)
1448
1449 Removes the specified filter *filt* from this handler.
1450
1451
1452.. method:: Handler.filter(record)
1453
1454 Applies this handler's filters to the record and returns a true value if the
1455 record is to be processed.
1456
1457
1458.. method:: Handler.flush()
1459
1460 Ensure all logging output has been flushed. This version does nothing and is
1461 intended to be implemented by subclasses.
1462
1463
1464.. method:: Handler.close()
1465
1466 Tidy up any resources used by the handler. This version does nothing and is
1467 intended to be implemented by subclasses.
1468
1469
1470.. method:: Handler.handle(record)
1471
1472 Conditionally emits the specified logging record, depending on filters which may
1473 have been added to the handler. Wraps the actual emission of the record with
1474 acquisition/release of the I/O thread lock.
1475
1476
1477.. method:: Handler.handleError(record)
1478
1479 This method should be called from handlers when an exception is encountered
1480 during an :meth:`emit` call. By default it does nothing, which means that
1481 exceptions get silently ignored. This is what is mostly wanted for a logging
1482 system - most users will not care about errors in the logging system, they are
1483 more interested in application errors. You could, however, replace this with a
1484 custom handler if you wish. The specified record is the one which was being
1485 processed when the exception occurred.
1486
1487
1488.. method:: Handler.format(record)
1489
1490 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1491 default formatter for the module.
1492
1493
1494.. method:: Handler.emit(record)
1495
1496 Do whatever it takes to actually log the specified logging record. This version
1497 is intended to be implemented by subclasses and so raises a
1498 :exc:`NotImplementedError`.
1499
1500
1501StreamHandler
1502^^^^^^^^^^^^^
1503
1504The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1505sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1506file-like object (or, more precisely, any object which supports :meth:`write`
1507and :meth:`flush` methods).
1508
1509
1510.. class:: StreamHandler([strm])
1511
1512 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1513 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1514 will be used.
1515
1516
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001517 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001518
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001519 If a formatter is specified, it is used to format the record. The record
1520 is then written to the stream with a trailing newline. If exception
1521 information is present, it is formatted using
1522 :func:`traceback.print_exception` and appended to the stream.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001523
1524
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001525 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001526
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001527 Flushes the stream by calling its :meth:`flush` method. Note that the
1528 :meth:`close` method is inherited from :class:`Handler` and so does
1529 nothing, so an explicit :meth:`flush` call may be needed at times.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001530
1531
1532FileHandler
1533^^^^^^^^^^^
1534
1535The :class:`FileHandler` class, located in the core :mod:`logging` package,
1536sends logging output to a disk file. It inherits the output functionality from
1537:class:`StreamHandler`.
1538
1539
Vinay Sajipf38ba782008-01-24 12:38:30 +00001540.. class:: FileHandler(filename[, mode[, encoding[, delay]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001541
1542 Returns a new instance of the :class:`FileHandler` class. The specified file is
1543 opened and used as the stream for logging. If *mode* is not specified,
1544 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
Vinay Sajipf38ba782008-01-24 12:38:30 +00001545 with that encoding. If *delay* is true, then file opening is deferred until the
1546 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001547
1548
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001549 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001550
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001551 Closes the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001552
1553
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001554 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001555
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001556 Outputs the record to the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001557
1558
1559WatchedFileHandler
1560^^^^^^^^^^^^^^^^^^
1561
1562.. versionadded:: 2.6
1563
1564The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1565module, is a :class:`FileHandler` which watches the file it is logging to. If
1566the file changes, it is closed and reopened using the file name.
1567
1568A file change can happen because of usage of programs such as *newsyslog* and
1569*logrotate* which perform log file rotation. This handler, intended for use
1570under Unix/Linux, watches the file to see if it has changed since the last emit.
1571(A file is deemed to have changed if its device or inode have changed.) If the
1572file has changed, the old file stream is closed, and the file opened to get a
1573new stream.
1574
1575This handler is not appropriate for use under Windows, because under Windows
1576open log files cannot be moved or renamed - logging opens the files with
1577exclusive locks - and so there is no need for such a handler. Furthermore,
1578*ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1579this value.
1580
1581
Vinay Sajipf38ba782008-01-24 12:38:30 +00001582.. class:: WatchedFileHandler(filename[,mode[, encoding[, delay]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001583
1584 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1585 file is opened and used as the stream for logging. If *mode* is not specified,
1586 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
Vinay Sajipf38ba782008-01-24 12:38:30 +00001587 with that encoding. If *delay* is true, then file opening is deferred until the
1588 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001589
1590
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001591 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001592
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001593 Outputs the record to the file, but first checks to see if the file has
1594 changed. If it has, the existing stream is flushed and closed and the
1595 file opened again, before outputting the record to the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001596
1597
1598RotatingFileHandler
1599^^^^^^^^^^^^^^^^^^^
1600
1601The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1602module, supports rotation of disk log files.
1603
1604
Vinay Sajipf38ba782008-01-24 12:38:30 +00001605.. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount[, encoding[, delay]]]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001606
1607 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1608 file is opened and used as the stream for logging. If *mode* is not specified,
Vinay Sajipf38ba782008-01-24 12:38:30 +00001609 ``'a'`` is used. If *encoding* is not *None*, it is used to open the file
1610 with that encoding. If *delay* is true, then file opening is deferred until the
1611 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001612
1613 You can use the *maxBytes* and *backupCount* values to allow the file to
1614 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1615 the file is closed and a new file is silently opened for output. Rollover occurs
1616 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1617 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1618 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1619 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1620 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1621 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1622 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1623 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1624 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1625
1626
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001627 .. method:: doRollover()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001628
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001629 Does a rollover, as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001630
1631
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001632 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001633
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001634 Outputs the record to the file, catering for rollover as described
1635 previously.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001636
1637
1638TimedRotatingFileHandler
1639^^^^^^^^^^^^^^^^^^^^^^^^
1640
1641The :class:`TimedRotatingFileHandler` class, located in the
1642:mod:`logging.handlers` module, supports rotation of disk log files at certain
1643timed intervals.
1644
1645
Vinay Sajipf38ba782008-01-24 12:38:30 +00001646.. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount[, encoding[, delay]]]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001647
1648 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1649 specified file is opened and used as the stream for logging. On rotating it also
1650 sets the filename suffix. Rotating happens based on the product of *when* and
1651 *interval*.
1652
1653 You can use the *when* to specify the type of *interval*. The list of possible
1654 values is, note that they are not case sensitive:
1655
Georg Brandl72780a42008-03-02 13:41:39 +00001656 +----------------+-----------------------+
1657 | Value | Type of interval |
1658 +================+=======================+
1659 | ``'S'`` | Seconds |
1660 +----------------+-----------------------+
1661 | ``'M'`` | Minutes |
1662 +----------------+-----------------------+
1663 | ``'H'`` | Hours |
1664 +----------------+-----------------------+
1665 | ``'D'`` | Days |
1666 +----------------+-----------------------+
1667 | ``'W'`` | Week day (0=Monday) |
1668 +----------------+-----------------------+
1669 | ``'midnight'`` | Roll over at midnight |
1670 +----------------+-----------------------+
Georg Brandl8ec7f652007-08-15 14:28:01 +00001671
Georg Brandle6dab2a2008-03-02 14:15:04 +00001672 The system will save old log files by appending extensions to the filename.
1673 The extensions are date-and-time based, using the strftime format
Vinay Sajip89a01cd2008-04-02 21:17:25 +00001674 ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on the
1675 rollover interval. If *backupCount* is nonzero, at most *backupCount* files
1676 will be kept, and if more would be created when rollover occurs, the oldest
1677 one is deleted. The deletion logic uses the interval to determine which
1678 files to delete, so changing the interval may leave old files lying around.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001679
1680
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001681 .. method:: doRollover()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001682
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001683 Does a rollover, as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001684
1685
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001686 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001687
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001688 Outputs the record to the file, catering for rollover as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001689
1690
1691SocketHandler
1692^^^^^^^^^^^^^
1693
1694The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1695sends logging output to a network socket. The base class uses a TCP socket.
1696
1697
1698.. class:: SocketHandler(host, port)
1699
1700 Returns a new instance of the :class:`SocketHandler` class intended to
1701 communicate with a remote machine whose address is given by *host* and *port*.
1702
1703
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001704 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001705
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001706 Closes the socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001707
1708
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001709 .. method:: emit()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001710
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001711 Pickles the record's attribute dictionary and writes it to the socket in
1712 binary format. If there is an error with the socket, silently drops the
1713 packet. If the connection was previously lost, re-establishes the
1714 connection. To unpickle the record at the receiving end into a
1715 :class:`LogRecord`, use the :func:`makeLogRecord` function.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001716
1717
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001718 .. method:: handleError()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001719
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001720 Handles an error which has occurred during :meth:`emit`. The most likely
1721 cause is a lost connection. Closes the socket so that we can retry on the
1722 next event.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001723
1724
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001725 .. method:: makeSocket()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001726
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001727 This is a factory method which allows subclasses to define the precise
1728 type of socket they want. The default implementation creates a TCP socket
1729 (:const:`socket.SOCK_STREAM`).
Georg Brandl8ec7f652007-08-15 14:28:01 +00001730
1731
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001732 .. method:: makePickle(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001733
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001734 Pickles the record's attribute dictionary in binary format with a length
1735 prefix, and returns it ready for transmission across the socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001736
1737
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001738 .. method:: send(packet)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001739
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001740 Send a pickled string *packet* to the socket. This function allows for
1741 partial sends which can happen when the network is busy.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001742
1743
1744DatagramHandler
1745^^^^^^^^^^^^^^^
1746
1747The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1748module, inherits from :class:`SocketHandler` to support sending logging messages
1749over UDP sockets.
1750
1751
1752.. class:: DatagramHandler(host, port)
1753
1754 Returns a new instance of the :class:`DatagramHandler` class intended to
1755 communicate with a remote machine whose address is given by *host* and *port*.
1756
1757
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001758 .. method:: emit()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001759
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001760 Pickles the record's attribute dictionary and writes it to the socket in
1761 binary format. If there is an error with the socket, silently drops the
1762 packet. To unpickle the record at the receiving end into a
1763 :class:`LogRecord`, use the :func:`makeLogRecord` function.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001764
1765
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001766 .. method:: makeSocket()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001767
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001768 The factory method of :class:`SocketHandler` is here overridden to create
1769 a UDP socket (:const:`socket.SOCK_DGRAM`).
Georg Brandl8ec7f652007-08-15 14:28:01 +00001770
1771
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001772 .. method:: send(s)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001773
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001774 Send a pickled string to a socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001775
1776
1777SysLogHandler
1778^^^^^^^^^^^^^
1779
1780The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1781supports sending logging messages to a remote or local Unix syslog.
1782
1783
1784.. class:: SysLogHandler([address[, facility]])
1785
1786 Returns a new instance of the :class:`SysLogHandler` class intended to
1787 communicate with a remote Unix machine whose address is given by *address* in
1788 the form of a ``(host, port)`` tuple. If *address* is not specified,
1789 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1790 alternative to providing a ``(host, port)`` tuple is providing an address as a
1791 string, for example "/dev/log". In this case, a Unix domain socket is used to
1792 send the message to the syslog. If *facility* is not specified,
1793 :const:`LOG_USER` is used.
1794
1795
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001796 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001797
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001798 Closes the socket to the remote host.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001799
1800
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001801 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001802
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001803 The record is formatted, and then sent to the syslog server. If exception
1804 information is present, it is *not* sent to the server.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001805
1806
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001807 .. method:: encodePriority(facility, priority)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001808
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001809 Encodes the facility and priority into an integer. You can pass in strings
1810 or integers - if strings are passed, internal mapping dictionaries are
1811 used to convert them to integers.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001812
1813
1814NTEventLogHandler
1815^^^^^^^^^^^^^^^^^
1816
1817The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1818module, supports sending logging messages to a local Windows NT, Windows 2000 or
1819Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1820extensions for Python installed.
1821
1822
1823.. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1824
1825 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1826 used to define the application name as it appears in the event log. An
1827 appropriate registry entry is created using this name. The *dllname* should give
1828 the fully qualified pathname of a .dll or .exe which contains message
1829 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1830 - this is installed with the Win32 extensions and contains some basic
1831 placeholder message definitions. Note that use of these placeholders will make
1832 your event logs big, as the entire message source is held in the log. If you
1833 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1834 contains the message definitions you want to use in the event log). The
1835 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1836 defaults to ``'Application'``.
1837
1838
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001839 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001840
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001841 At this point, you can remove the application name from the registry as a
1842 source of event log entries. However, if you do this, you will not be able
1843 to see the events as you intended in the Event Log Viewer - it needs to be
1844 able to access the registry to get the .dll name. The current version does
1845 not do this (in fact it doesn't do anything).
Georg Brandl8ec7f652007-08-15 14:28:01 +00001846
1847
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001848 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001849
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001850 Determines the message ID, event category and event type, and then logs
1851 the message in the NT event log.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001852
1853
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001854 .. method:: getEventCategory(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001855
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001856 Returns the event category for the record. Override this if you want to
1857 specify your own categories. This version returns 0.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001858
1859
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001860 .. method:: getEventType(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001861
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001862 Returns the event type for the record. Override this if you want to
1863 specify your own types. This version does a mapping using the handler's
1864 typemap attribute, which is set up in :meth:`__init__` to a dictionary
1865 which contains mappings for :const:`DEBUG`, :const:`INFO`,
1866 :const:`WARNING`, :const:`ERROR` and :const:`CRITICAL`. If you are using
1867 your own levels, you will either need to override this method or place a
1868 suitable dictionary in the handler's *typemap* attribute.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001869
1870
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001871 .. method:: getMessageID(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001872
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001873 Returns the message ID for the record. If you are using your own messages,
1874 you could do this by having the *msg* passed to the logger being an ID
1875 rather than a format string. Then, in here, you could use a dictionary
1876 lookup to get the message ID. This version returns 1, which is the base
1877 message ID in :file:`win32service.pyd`.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001878
1879
1880SMTPHandler
1881^^^^^^^^^^^
1882
1883The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1884supports sending logging messages to an email address via SMTP.
1885
1886
1887.. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1888
1889 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1890 initialized with the from and to addresses and subject line of the email. The
1891 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1892 the (host, port) tuple format for the *mailhost* argument. If you use a string,
1893 the standard SMTP port is used. If your SMTP server requires authentication, you
1894 can specify a (username, password) tuple for the *credentials* argument.
1895
1896 .. versionchanged:: 2.6
1897 *credentials* was added.
1898
1899
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001900 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001901
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001902 Formats the record and sends it to the specified addressees.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001903
1904
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001905 .. method:: getSubject(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001906
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001907 If you want to specify a subject line which is record-dependent, override
1908 this method.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001909
1910
1911MemoryHandler
1912^^^^^^^^^^^^^
1913
1914The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
1915supports buffering of logging records in memory, periodically flushing them to a
1916:dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
1917event of a certain severity or greater is seen.
1918
1919:class:`MemoryHandler` is a subclass of the more general
1920:class:`BufferingHandler`, which is an abstract class. This buffers logging
1921records in memory. Whenever each record is added to the buffer, a check is made
1922by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
1923should, then :meth:`flush` is expected to do the needful.
1924
1925
1926.. class:: BufferingHandler(capacity)
1927
1928 Initializes the handler with a buffer of the specified capacity.
1929
1930
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001931 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001932
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001933 Appends the record to the buffer. If :meth:`shouldFlush` returns true,
1934 calls :meth:`flush` to process the buffer.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001935
1936
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001937 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001938
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001939 You can override this to implement custom flushing behavior. This version
1940 just zaps the buffer to empty.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001941
1942
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001943 .. method:: shouldFlush(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001944
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001945 Returns true if the buffer is up to capacity. This method can be
1946 overridden to implement custom flushing strategies.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001947
1948
1949.. class:: MemoryHandler(capacity[, flushLevel [, target]])
1950
1951 Returns a new instance of the :class:`MemoryHandler` class. The instance is
1952 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
1953 :const:`ERROR` is used. If no *target* is specified, the target will need to be
1954 set using :meth:`setTarget` before this handler does anything useful.
1955
1956
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001957 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001958
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001959 Calls :meth:`flush`, sets the target to :const:`None` and clears the
1960 buffer.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001961
1962
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001963 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001964
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001965 For a :class:`MemoryHandler`, flushing means just sending the buffered
1966 records to the target, if there is one. Override if you want different
1967 behavior.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001968
1969
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001970 .. method:: setTarget(target)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001971
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001972 Sets the target handler for this handler.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001973
1974
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001975 .. method:: shouldFlush(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001976
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001977 Checks for buffer full or a record at the *flushLevel* or higher.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001978
1979
1980HTTPHandler
1981^^^^^^^^^^^
1982
1983The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
1984supports sending logging messages to a Web server, using either ``GET`` or
1985``POST`` semantics.
1986
1987
1988.. class:: HTTPHandler(host, url[, method])
1989
1990 Returns a new instance of the :class:`HTTPHandler` class. The instance is
1991 initialized with a host address, url and HTTP method. The *host* can be of the
1992 form ``host:port``, should you need to use a specific port number. If no
1993 *method* is specified, ``GET`` is used.
1994
1995
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001996 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001997
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001998 Sends the record to the Web server as an URL-encoded dictionary.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001999
2000
Georg Brandlc37f2882007-12-04 17:46:27 +00002001.. _formatter-objects:
2002
Georg Brandl8ec7f652007-08-15 14:28:01 +00002003Formatter Objects
2004-----------------
2005
2006:class:`Formatter`\ s have the following attributes and methods. They are
2007responsible for converting a :class:`LogRecord` to (usually) a string which can
2008be interpreted by either a human or an external system. The base
2009:class:`Formatter` allows a formatting string to be specified. If none is
2010supplied, the default value of ``'%(message)s'`` is used.
2011
2012A Formatter can be initialized with a format string which makes use of knowledge
2013of the :class:`LogRecord` attributes - such as the default value mentioned above
2014making use of the fact that the user's message and arguments are pre-formatted
2015into a :class:`LogRecord`'s *message* attribute. This format string contains
2016standard python %-style mapping keys. See section :ref:`string-formatting`
2017for more information on string formatting.
2018
2019Currently, the useful mapping keys in a :class:`LogRecord` are:
2020
2021+-------------------------+-----------------------------------------------+
2022| Format | Description |
2023+=========================+===============================================+
2024| ``%(name)s`` | Name of the logger (logging channel). |
2025+-------------------------+-----------------------------------------------+
2026| ``%(levelno)s`` | Numeric logging level for the message |
2027| | (:const:`DEBUG`, :const:`INFO`, |
2028| | :const:`WARNING`, :const:`ERROR`, |
2029| | :const:`CRITICAL`). |
2030+-------------------------+-----------------------------------------------+
2031| ``%(levelname)s`` | Text logging level for the message |
2032| | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
2033| | ``'ERROR'``, ``'CRITICAL'``). |
2034+-------------------------+-----------------------------------------------+
2035| ``%(pathname)s`` | Full pathname of the source file where the |
2036| | logging call was issued (if available). |
2037+-------------------------+-----------------------------------------------+
2038| ``%(filename)s`` | Filename portion of pathname. |
2039+-------------------------+-----------------------------------------------+
2040| ``%(module)s`` | Module (name portion of filename). |
2041+-------------------------+-----------------------------------------------+
2042| ``%(funcName)s`` | Name of function containing the logging call. |
2043+-------------------------+-----------------------------------------------+
2044| ``%(lineno)d`` | Source line number where the logging call was |
2045| | issued (if available). |
2046+-------------------------+-----------------------------------------------+
2047| ``%(created)f`` | Time when the :class:`LogRecord` was created |
2048| | (as returned by :func:`time.time`). |
2049+-------------------------+-----------------------------------------------+
2050| ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
2051| | created, relative to the time the logging |
2052| | module was loaded. |
2053+-------------------------+-----------------------------------------------+
2054| ``%(asctime)s`` | Human-readable time when the |
2055| | :class:`LogRecord` was created. By default |
2056| | this is of the form "2003-07-08 16:49:45,896" |
2057| | (the numbers after the comma are millisecond |
2058| | portion of the time). |
2059+-------------------------+-----------------------------------------------+
2060| ``%(msecs)d`` | Millisecond portion of the time when the |
2061| | :class:`LogRecord` was created. |
2062+-------------------------+-----------------------------------------------+
2063| ``%(thread)d`` | Thread ID (if available). |
2064+-------------------------+-----------------------------------------------+
2065| ``%(threadName)s`` | Thread name (if available). |
2066+-------------------------+-----------------------------------------------+
2067| ``%(process)d`` | Process ID (if available). |
2068+-------------------------+-----------------------------------------------+
2069| ``%(message)s`` | The logged message, computed as ``msg % |
2070| | args``. |
2071+-------------------------+-----------------------------------------------+
2072
2073.. versionchanged:: 2.5
2074 *funcName* was added.
2075
2076
2077.. class:: Formatter([fmt[, datefmt]])
2078
2079 Returns a new instance of the :class:`Formatter` class. The instance is
2080 initialized with a format string for the message as a whole, as well as a format
2081 string for the date/time portion of a message. If no *fmt* is specified,
2082 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
2083 is used.
2084
2085
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002086 .. method:: format(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002087
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002088 The record's attribute dictionary is used as the operand to a string
2089 formatting operation. Returns the resulting string. Before formatting the
2090 dictionary, a couple of preparatory steps are carried out. The *message*
2091 attribute of the record is computed using *msg* % *args*. If the
2092 formatting string contains ``'(asctime)'``, :meth:`formatTime` is called
2093 to format the event time. If there is exception information, it is
2094 formatted using :meth:`formatException` and appended to the message. Note
2095 that the formatted exception information is cached in attribute
2096 *exc_text*. This is useful because the exception information can be
2097 pickled and sent across the wire, but you should be careful if you have
2098 more than one :class:`Formatter` subclass which customizes the formatting
2099 of exception information. In this case, you will have to clear the cached
2100 value after a formatter has done its formatting, so that the next
2101 formatter to handle the event doesn't use the cached value but
2102 recalculates it afresh.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002103
2104
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002105 .. method:: formatTime(record[, datefmt])
Georg Brandl8ec7f652007-08-15 14:28:01 +00002106
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002107 This method should be called from :meth:`format` by a formatter which
2108 wants to make use of a formatted time. This method can be overridden in
2109 formatters to provide for any specific requirement, but the basic behavior
2110 is as follows: if *datefmt* (a string) is specified, it is used with
2111 :func:`time.strftime` to format the creation time of the
2112 record. Otherwise, the ISO8601 format is used. The resulting string is
2113 returned.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002114
2115
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002116 .. method:: formatException(exc_info)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002117
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002118 Formats the specified exception information (a standard exception tuple as
2119 returned by :func:`sys.exc_info`) as a string. This default implementation
2120 just uses :func:`traceback.print_exception`. The resulting string is
2121 returned.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002122
2123
2124Filter Objects
2125--------------
2126
2127:class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
2128more sophisticated filtering than is provided by levels. The base filter class
2129only allows events which are below a certain point in the logger hierarchy. For
2130example, a filter initialized with "A.B" will allow events logged by loggers
2131"A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
2132initialized with the empty string, all events are passed.
2133
2134
2135.. class:: Filter([name])
2136
2137 Returns an instance of the :class:`Filter` class. If *name* is specified, it
2138 names a logger which, together with its children, will have its events allowed
2139 through the filter. If no name is specified, allows every event.
2140
2141
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002142 .. method:: filter(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002143
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002144 Is the specified record to be logged? Returns zero for no, nonzero for
2145 yes. If deemed appropriate, the record may be modified in-place by this
2146 method.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002147
2148
2149LogRecord Objects
2150-----------------
2151
2152:class:`LogRecord` instances are created every time something is logged. They
2153contain all the information pertinent to the event being logged. The main
2154information passed in is in msg and args, which are combined using msg % args to
2155create the message field of the record. The record also includes information
2156such as when the record was created, the source line where the logging call was
2157made, and any exception information to be logged.
2158
2159
2160.. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2161
2162 Returns an instance of :class:`LogRecord` initialized with interesting
2163 information. The *name* is the logger name; *lvl* is the numeric level;
2164 *pathname* is the absolute pathname of the source file in which the logging
2165 call was made; *lineno* is the line number in that file where the logging
2166 call is found; *msg* is the user-supplied message (a format string); *args*
2167 is the tuple which, together with *msg*, makes up the user message; and
2168 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2169 (or :const:`None`, if no exception information is available). The *func* is
2170 the name of the function from which the logging call was made. If not
2171 specified, it defaults to ``None``.
2172
2173 .. versionchanged:: 2.5
2174 *func* was added.
2175
2176
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002177 .. method:: getMessage()
Georg Brandl8ec7f652007-08-15 14:28:01 +00002178
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002179 Returns the message for this :class:`LogRecord` instance after merging any
2180 user-supplied arguments with the message.
2181
Georg Brandl8ec7f652007-08-15 14:28:01 +00002182
Vinay Sajipc7403352008-01-18 15:54:14 +00002183LoggerAdapter Objects
2184---------------------
2185
2186.. versionadded:: 2.6
2187
2188:class:`LoggerAdapter` instances are used to conveniently pass contextual
Vinay Sajip733024a2008-01-21 17:39:22 +00002189information into logging calls. For a usage example , see the section on
2190`adding contextual information to your logging output`__.
2191
2192__ context-info_
Vinay Sajipc7403352008-01-18 15:54:14 +00002193
2194.. class:: LoggerAdapter(logger, extra)
2195
2196 Returns an instance of :class:`LoggerAdapter` initialized with an
2197 underlying :class:`Logger` instance and a dict-like object.
2198
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002199 .. method:: process(msg, kwargs)
Vinay Sajipc7403352008-01-18 15:54:14 +00002200
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002201 Modifies the message and/or keyword arguments passed to a logging call in
2202 order to insert contextual information. This implementation takes the object
2203 passed as *extra* to the constructor and adds it to *kwargs* using key
2204 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
2205 (possibly modified) versions of the arguments passed in.
Vinay Sajipc7403352008-01-18 15:54:14 +00002206
2207In addition to the above, :class:`LoggerAdapter` supports all the logging
2208methods of :class:`Logger`, i.e. :meth:`debug`, :meth:`info`, :meth:`warning`,
2209:meth:`error`, :meth:`exception`, :meth:`critical` and :meth:`log`. These
2210methods have the same signatures as their counterparts in :class:`Logger`, so
2211you can use the two types of instances interchangeably.
2212
Georg Brandl8ec7f652007-08-15 14:28:01 +00002213
2214Thread Safety
2215-------------
2216
2217The logging module is intended to be thread-safe without any special work
2218needing to be done by its clients. It achieves this though using threading
2219locks; there is one lock to serialize access to the module's shared data, and
2220each handler also creates a lock to serialize access to its underlying I/O.
2221
2222
2223Configuration
2224-------------
2225
2226
2227.. _logging-config-api:
2228
2229Configuration functions
2230^^^^^^^^^^^^^^^^^^^^^^^
2231
Georg Brandl8ec7f652007-08-15 14:28:01 +00002232The following functions configure the logging module. They are located in the
2233:mod:`logging.config` module. Their use is optional --- you can configure the
2234logging module using these functions or by making calls to the main API (defined
2235in :mod:`logging` itself) and defining handlers which are declared either in
2236:mod:`logging` or :mod:`logging.handlers`.
2237
2238
2239.. function:: fileConfig(fname[, defaults])
2240
2241 Reads the logging configuration from a ConfigParser-format file named *fname*.
2242 This function can be called several times from an application, allowing an end
2243 user the ability to select from various pre-canned configurations (if the
2244 developer provides a mechanism to present the choices and load the chosen
2245 configuration). Defaults to be passed to ConfigParser can be specified in the
2246 *defaults* argument.
2247
2248
2249.. function:: listen([port])
2250
2251 Starts up a socket server on the specified port, and listens for new
2252 configurations. If no port is specified, the module's default
2253 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2254 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2255 :class:`Thread` instance on which you can call :meth:`start` to start the
2256 server, and which you can :meth:`join` when appropriate. To stop the server,
Georg Brandlc37f2882007-12-04 17:46:27 +00002257 call :func:`stopListening`.
2258
2259 To send a configuration to the socket, read in the configuration file and
2260 send it to the socket as a string of bytes preceded by a four-byte length
2261 string packed in binary using ``struct.pack('>L', n)``.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002262
2263
2264.. function:: stopListening()
2265
Georg Brandlc37f2882007-12-04 17:46:27 +00002266 Stops the listening server which was created with a call to :func:`listen`.
2267 This is typically called before calling :meth:`join` on the return value from
Georg Brandl8ec7f652007-08-15 14:28:01 +00002268 :func:`listen`.
2269
2270
2271.. _logging-config-fileformat:
2272
2273Configuration file format
2274^^^^^^^^^^^^^^^^^^^^^^^^^
2275
Georg Brandl8ec7f652007-08-15 14:28:01 +00002276The configuration file format understood by :func:`fileConfig` is based on
2277ConfigParser functionality. The file must contain sections called ``[loggers]``,
2278``[handlers]`` and ``[formatters]`` which identify by name the entities of each
2279type which are defined in the file. For each such entity, there is a separate
2280section which identified how that entity is configured. Thus, for a logger named
2281``log01`` in the ``[loggers]`` section, the relevant configuration details are
2282held in a section ``[logger_log01]``. Similarly, a handler called ``hand01`` in
2283the ``[handlers]`` section will have its configuration held in a section called
2284``[handler_hand01]``, while a formatter called ``form01`` in the
2285``[formatters]`` section will have its configuration specified in a section
2286called ``[formatter_form01]``. The root logger configuration must be specified
2287in a section called ``[logger_root]``.
2288
2289Examples of these sections in the file are given below. ::
2290
2291 [loggers]
2292 keys=root,log02,log03,log04,log05,log06,log07
2293
2294 [handlers]
2295 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2296
2297 [formatters]
2298 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2299
2300The root logger must specify a level and a list of handlers. An example of a
2301root logger section is given below. ::
2302
2303 [logger_root]
2304 level=NOTSET
2305 handlers=hand01
2306
2307The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2308``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2309logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2310package's namespace.
2311
2312The ``handlers`` entry is a comma-separated list of handler names, which must
2313appear in the ``[handlers]`` section. These names must appear in the
2314``[handlers]`` section and have corresponding sections in the configuration
2315file.
2316
2317For loggers other than the root logger, some additional information is required.
2318This is illustrated by the following example. ::
2319
2320 [logger_parser]
2321 level=DEBUG
2322 handlers=hand01
2323 propagate=1
2324 qualname=compiler.parser
2325
2326The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2327except that if a non-root logger's level is specified as ``NOTSET``, the system
2328consults loggers higher up the hierarchy to determine the effective level of the
2329logger. The ``propagate`` entry is set to 1 to indicate that messages must
2330propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2331indicate that messages are **not** propagated to handlers up the hierarchy. The
2332``qualname`` entry is the hierarchical channel name of the logger, that is to
2333say the name used by the application to get the logger.
2334
2335Sections which specify handler configuration are exemplified by the following.
2336::
2337
2338 [handler_hand01]
2339 class=StreamHandler
2340 level=NOTSET
2341 formatter=form01
2342 args=(sys.stdout,)
2343
2344The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2345in the ``logging`` package's namespace). The ``level`` is interpreted as for
2346loggers, and ``NOTSET`` is taken to mean "log everything".
2347
2348The ``formatter`` entry indicates the key name of the formatter for this
2349handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2350If a name is specified, it must appear in the ``[formatters]`` section and have
2351a corresponding section in the configuration file.
2352
2353The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2354package's namespace, is the list of arguments to the constructor for the handler
2355class. Refer to the constructors for the relevant handlers, or to the examples
2356below, to see how typical entries are constructed. ::
2357
2358 [handler_hand02]
2359 class=FileHandler
2360 level=DEBUG
2361 formatter=form02
2362 args=('python.log', 'w')
2363
2364 [handler_hand03]
2365 class=handlers.SocketHandler
2366 level=INFO
2367 formatter=form03
2368 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2369
2370 [handler_hand04]
2371 class=handlers.DatagramHandler
2372 level=WARN
2373 formatter=form04
2374 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2375
2376 [handler_hand05]
2377 class=handlers.SysLogHandler
2378 level=ERROR
2379 formatter=form05
2380 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2381
2382 [handler_hand06]
2383 class=handlers.NTEventLogHandler
2384 level=CRITICAL
2385 formatter=form06
2386 args=('Python Application', '', 'Application')
2387
2388 [handler_hand07]
2389 class=handlers.SMTPHandler
2390 level=WARN
2391 formatter=form07
2392 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2393
2394 [handler_hand08]
2395 class=handlers.MemoryHandler
2396 level=NOTSET
2397 formatter=form08
2398 target=
2399 args=(10, ERROR)
2400
2401 [handler_hand09]
2402 class=handlers.HTTPHandler
2403 level=NOTSET
2404 formatter=form09
2405 args=('localhost:9022', '/log', 'GET')
2406
2407Sections which specify formatter configuration are typified by the following. ::
2408
2409 [formatter_form01]
2410 format=F1 %(asctime)s %(levelname)s %(message)s
2411 datefmt=
2412 class=logging.Formatter
2413
2414The ``format`` entry is the overall format string, and the ``datefmt`` entry is
Georg Brandlb19be572007-12-29 10:57:00 +00002415the :func:`strftime`\ -compatible date/time format string. If empty, the
2416package substitutes ISO8601 format date/times, which is almost equivalent to
2417specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2418also specifies milliseconds, which are appended to the result of using the above
2419format string, with a comma separator. An example time in ISO8601 format is
2420``2003-01-23 00:29:50,411``.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002421
2422The ``class`` entry is optional. It indicates the name of the formatter's class
2423(as a dotted module and class name.) This option is useful for instantiating a
2424:class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2425exception tracebacks in an expanded or condensed format.
2426
Georg Brandlc37f2882007-12-04 17:46:27 +00002427
2428Configuration server example
2429^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2430
2431Here is an example of a module using the logging configuration server::
2432
2433 import logging
2434 import logging.config
2435 import time
2436 import os
2437
2438 # read initial config file
2439 logging.config.fileConfig("logging.conf")
2440
2441 # create and start listener on port 9999
2442 t = logging.config.listen(9999)
2443 t.start()
2444
2445 logger = logging.getLogger("simpleExample")
2446
2447 try:
2448 # loop through logging calls to see the difference
2449 # new configurations make, until Ctrl+C is pressed
2450 while True:
2451 logger.debug("debug message")
2452 logger.info("info message")
2453 logger.warn("warn message")
2454 logger.error("error message")
2455 logger.critical("critical message")
2456 time.sleep(5)
2457 except KeyboardInterrupt:
2458 # cleanup
2459 logging.config.stopListening()
2460 t.join()
2461
2462And here is a script that takes a filename and sends that file to the server,
2463properly preceded with the binary-encoded length, as the new logging
2464configuration::
2465
2466 #!/usr/bin/env python
2467 import socket, sys, struct
2468
2469 data_to_send = open(sys.argv[1], "r").read()
2470
2471 HOST = 'localhost'
2472 PORT = 9999
2473 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2474 print "connecting..."
2475 s.connect((HOST, PORT))
2476 print "sending config..."
2477 s.send(struct.pack(">L", len(data_to_send)))
2478 s.send(data_to_send)
2479 s.close()
2480 print "complete"
2481
2482
2483More examples
2484-------------
2485
2486Multiple handlers and formatters
2487^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2488
2489Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2490or maximum quota for the number of handlers you may add. Sometimes it will be
2491beneficial for an application to log all messages of all severities to a text
2492file while simultaneously logging errors or above to the console. To set this
2493up, simply configure the appropriate handlers. The logging calls in the
2494application code will remain unchanged. Here is a slight modification to the
2495previous simple module-based configuration example::
2496
2497 import logging
2498
2499 logger = logging.getLogger("simple_example")
2500 logger.setLevel(logging.DEBUG)
2501 # create file handler which logs even debug messages
2502 fh = logging.FileHandler("spam.log")
2503 fh.setLevel(logging.DEBUG)
2504 # create console handler with a higher log level
2505 ch = logging.StreamHandler()
2506 ch.setLevel(logging.ERROR)
2507 # create formatter and add it to the handlers
2508 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2509 ch.setFormatter(formatter)
2510 fh.setFormatter(formatter)
2511 # add the handlers to logger
2512 logger.addHandler(ch)
2513 logger.addHandler(fh)
2514
2515 # "application" code
2516 logger.debug("debug message")
2517 logger.info("info message")
2518 logger.warn("warn message")
2519 logger.error("error message")
2520 logger.critical("critical message")
2521
2522Notice that the "application" code does not care about multiple handlers. All
2523that changed was the addition and configuration of a new handler named *fh*.
2524
2525The ability to create new handlers with higher- or lower-severity filters can be
2526very helpful when writing and testing an application. Instead of using many
2527``print`` statements for debugging, use ``logger.debug``: Unlike the print
2528statements, which you will have to delete or comment out later, the logger.debug
2529statements can remain intact in the source code and remain dormant until you
2530need them again. At that time, the only change that needs to happen is to
2531modify the severity level of the logger and/or handler to debug.
2532
2533
2534Using logging in multiple modules
2535^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2536
2537It was mentioned above that multiple calls to
2538``logging.getLogger('someLogger')`` return a reference to the same logger
2539object. This is true not only within the same module, but also across modules
2540as long as it is in the same Python interpreter process. It is true for
2541references to the same object; additionally, application code can define and
2542configure a parent logger in one module and create (but not configure) a child
2543logger in a separate module, and all logger calls to the child will pass up to
2544the parent. Here is a main module::
2545
2546 import logging
2547 import auxiliary_module
2548
2549 # create logger with "spam_application"
2550 logger = logging.getLogger("spam_application")
2551 logger.setLevel(logging.DEBUG)
2552 # create file handler which logs even debug messages
2553 fh = logging.FileHandler("spam.log")
2554 fh.setLevel(logging.DEBUG)
2555 # create console handler with a higher log level
2556 ch = logging.StreamHandler()
2557 ch.setLevel(logging.ERROR)
2558 # create formatter and add it to the handlers
2559 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2560 fh.setFormatter(formatter)
2561 ch.setFormatter(formatter)
2562 # add the handlers to the logger
2563 logger.addHandler(fh)
2564 logger.addHandler(ch)
2565
2566 logger.info("creating an instance of auxiliary_module.Auxiliary")
2567 a = auxiliary_module.Auxiliary()
2568 logger.info("created an instance of auxiliary_module.Auxiliary")
2569 logger.info("calling auxiliary_module.Auxiliary.do_something")
2570 a.do_something()
2571 logger.info("finished auxiliary_module.Auxiliary.do_something")
2572 logger.info("calling auxiliary_module.some_function()")
2573 auxiliary_module.some_function()
2574 logger.info("done with auxiliary_module.some_function()")
2575
2576Here is the auxiliary module::
2577
2578 import logging
2579
2580 # create logger
2581 module_logger = logging.getLogger("spam_application.auxiliary")
2582
2583 class Auxiliary:
2584 def __init__(self):
2585 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2586 self.logger.info("creating an instance of Auxiliary")
2587 def do_something(self):
2588 self.logger.info("doing something")
2589 a = 1 + 1
2590 self.logger.info("done doing something")
2591
2592 def some_function():
2593 module_logger.info("received a call to \"some_function\"")
2594
2595The output looks like this::
2596
Vinay Sajipe28fa292008-01-07 15:30:36 +00002597 2005-03-23 23:47:11,663 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002598 creating an instance of auxiliary_module.Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002599 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002600 creating an instance of Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002601 2005-03-23 23:47:11,665 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002602 created an instance of auxiliary_module.Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002603 2005-03-23 23:47:11,668 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002604 calling auxiliary_module.Auxiliary.do_something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002605 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002606 doing something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002607 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002608 done doing something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002609 2005-03-23 23:47:11,670 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002610 finished auxiliary_module.Auxiliary.do_something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002611 2005-03-23 23:47:11,671 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002612 calling auxiliary_module.some_function()
Vinay Sajipe28fa292008-01-07 15:30:36 +00002613 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002614 received a call to "some_function"
Vinay Sajipe28fa292008-01-07 15:30:36 +00002615 2005-03-23 23:47:11,673 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002616 done with auxiliary_module.some_function()
2617