1 :mod:`logging` --- Logging facility for Python
2 ==============================================
5 :synopsis: Flexible error logging system for applications.
8 .. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
9 .. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
12 .. index:: pair: Errors; logging
16 This module defines functions and classes which implement a flexible error
17 logging system for applications.
19 Logging is performed by calling methods on instances of the :class:`Logger`
20 class (hereafter called :dfn:`loggers`). Each instance has a name, and they are
21 conceptually arranged in a namespace hierarchy using dots (periods) as
22 separators. 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,
24 and indicate the area of an application in which a logged message originates.
26 Logged messages also have levels of importance associated with them. The default
27 levels provided are :const:`DEBUG`, :const:`INFO`, :const:`WARNING`,
28 :const:`ERROR` and :const:`CRITICAL`. As a convenience, you indicate the
29 importance 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
32 constrained 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.
39 The key benefit of having the logging API provided by a standard library module
40 is that all Python modules can participate in logging, so your application log
41 can include messages from third-party modules.
43 It is, of course, possible to log messages with different verbosity levels or to
44 different destinations. Support for writing log messages to files, HTTP
45 GET/POST locations, email via SMTP, generic sockets, or OS-specific logging
46 mechanisms are all supported by the standard module. You can also create your
47 own log destination class if you have special requirements not met by any of the
53 .. sectionauthor:: Doug Hellmann
54 .. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>)
56 Most applications are probably going to want to log to a file, so let's start
57 with that case. Using the :func:`basicConfig` function, we can set up the
58 default handler so that debug messages are written to a file::
61 LOG_FILENAME = '/tmp/logging_example.out'
62 logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,)
64 logging.debug('This message should go to the log file')
66 And now if we open the file and look at what we have, we should find the log
69 DEBUG:root:This message should go to the log file
71 If you run the script repeatedly, the additional log messages are appended to
72 the 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
74 yourself, though, it is simpler to use a :class:`RotatingFileHandler`::
78 import logging.handlers
80 LOG_FILENAME = '/tmp/logging_rotatingfile_example.out'
82 # Set up a specific logger with our desired output level
83 my_logger = logging.getLogger('MyLogger')
84 my_logger.setLevel(logging.DEBUG)
86 # Add the log message handler to the logger
87 handler = logging.handlers.RotatingFileHandler(
88 LOG_FILENAME, maxBytes=20, backupCount=5)
90 my_logger.addHandler(handler)
94 my_logger.debug('i = %d' % i)
96 # See what files are created
97 logfiles = glob.glob('%s*' % LOG_FILENAME)
99 for filename in logfiles:
102 The result should be 6 separate files, each with part of the log history for the
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
112 The most current file is always :file:`/tmp/logging_rotatingfile_example.out`,
113 and 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.
117 Obviously this example sets the log length much much too small as an extreme
118 example. You would want to set *maxBytes* to an appropriate value.
120 Another useful feature of the logging API is the ability to produce different
121 messages at different log levels. This allows you to instrument your code with
122 debug messages, for example, but turning the log level down so that those debug
123 messages are not written for your production system. The default levels are
124 ``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO``, ``DEBUG`` and ``UNSET``.
126 The logger, handler, and log message call each specify a level. The log message
127 is only emitted if the handler and logger are configured to emit messages of
128 that level or lower. For example, if a message is ``CRITICAL``, and the logger
129 is set to ``ERROR``, the message is emitted. If a message is a ``WARNING``, and
130 the logger is set to produce only ``ERROR``\s, the message is not emitted::
135 LEVELS = {'debug': logging.DEBUG,
136 'info': logging.INFO,
137 'warning': logging.WARNING,
138 'error': logging.ERROR,
139 'critical': logging.CRITICAL}
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)
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')
152 Run the script with an argument like 'debug' or 'warning' to see which messages
153 show up at different levels::
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
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
168 You will notice that these log messages all have ``root`` embedded in them. The
169 logging module supports a hierarchy of loggers with different names. An easy
170 way to tell where a specific log message comes from is to use a separate logger
171 object for each of your modules. Each new logger "inherits" the configuration
172 of its parent, and log messages sent to a logger include the name of that
173 logger. Optionally, each logger can be configured differently, so that messages
174 from different modules are handled in different ways. Let's look at a simple
175 example of how to log from different modules so it is easy to trace the source
180 logging.basicConfig(level=logging.WARNING)
182 logger1 = logging.getLogger('package1.module1')
183 logger2 = logging.getLogger('package2.module2')
185 logger1.warning('This message comes from one module')
186 logger2.warning('And this message comes from another module')
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
194 There are many more options for configuring logging, including different log
195 message formatting options, having messages delivered to multiple destinations,
196 and changing the configuration of a long-running application on the fly using a
197 socket interface. All of these options are covered in depth in the library
198 module documentation.
203 The logging library takes a modular approach and offers the several categories
204 of components: loggers, handlers, filters, and formatters. Loggers expose the
205 interface that application code directly uses. Handlers send the log records to
206 the appropriate destination. Filters provide a finer grained facility for
207 determining which log records to send on to a handler. Formatters specify the
208 layout of the resultant log record.
210 :class:`Logger` objects have a threefold job. First, they expose several
211 methods to application code so that applications can log messages at runtime.
212 Second, logger objects determine which log messages to act upon based upon
213 severity (the default filtering facility) or filter objects. Third, logger
214 objects pass along relevant log messages to all interested log handlers.
216 The most widely used methods on logger objects fall into two categories:
217 configuration and message sending.
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.
225 * :meth:`Logger.addFilter` and :meth:`Logger.removeFilter` add and remove filter
226 objects from the logger object. This tutorial does not address filters.
228 With the logger object configured, the following methods create log messages:
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.
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.
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.
248 :func:`getLogger` returns a reference to a logger instance with the specified
249 if it it is provided, or ``root`` if not. The names are period-separated
250 hierarchical structures. Multiple calls to :func:`getLogger` with the same name
251 will return a reference to the same logger object. Loggers that are further
252 down in the hierarchical list are children of loggers higher up in the list.
253 For 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``.
255 Child loggers propagate messages up to their parent loggers. Because of this,
256 it is unnecessary to define and configure all the loggers an application uses.
257 It is sufficient to configure a top-level logger and create child loggers as
264 :class:`Handler` objects are responsible for dispatching the appropriate log
265 messages (based on the log messages' severity) to the handler's specified
266 destination. Logger objects can add zero or more handler objects to themselves
267 with an :func:`addHandler` method. As an example scenario, an application may
268 want to send all log messages to a log file, all log messages of error or higher
269 to stdout, and all messages of critical to an email address. This scenario
270 requires three individual handlers where each handler is responsible for sending
271 messages of a specific severity to a specific location.
273 The standard library includes quite a few handler types; this tutorial uses only
274 :class:`StreamHandler` and :class:`FileHandler` in its examples.
276 There are very few methods in a handler for application developers to concern
277 themselves with. The only handler methods that seem relevant for application
278 developers who are using the built-in handler objects (that is, not creating
279 custom handlers) are the following configuration methods:
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.
288 * :func:`addFilter` and :func:`removeFilter` respectively configure and
289 deconfigure filter objects on handlers.
291 Application code should not directly instantiate and use handlers. Instead, the
292 :class:`Handler` class is a base class that defines the interface that all
293 Handlers should have and establishes some default behavior that child classes
294 can use (or override).
300 Formatter objects configure the final order, structure, and contents of the log
301 message. Unlike the base :class:`logging.Handler` class, application code may
302 instantiate formatter classes, although you could likely subclass the formatter
303 if your application needs special behavior. The constructor takes two optional
304 arguments: a message format string and a date format string. If there is no
305 message format string, the default is to use the raw message. If there is no
306 date format string, the default date format is::
310 with the milliseconds tacked on at the end.
312 The message format string uses ``%(<dictionary key>)s`` styled string
313 substitution; the possible keys are documented in :ref:`formatter-objects`.
315 The following message format string will log the time in a human-readable
316 format, the severity of the message, and the contents of the message, in that
319 "%(asctime)s - %(levelname)s - %(message)s"
325 Programmers can configure logging either by creating loggers, handlers, and
326 formatters explicitly in a main module with the configuration methods listed
327 above (using Python code), or by creating a logging config file. The following
328 code is an example of configuring a very simple logger, a console handler, and a
329 simple formatter in a Python module::
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)
340 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
341 # add formatter to ch
342 ch.setFormatter(formatter)
344 logger.addHandler(ch)
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")
353 Running this module from the command line produces the following output::
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
362 The following Python module creates a logger, handler, and formatter nearly
363 identical to those in the example listed above, with the only difference being
364 the names of the objects::
367 import logging.config
369 logging.config.fileConfig("logging.conf")
372 logger = logging.getLogger("simpleExample")
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")
381 Here is the logging.conf file::
384 keys=root,simpleExample
394 handlers=consoleHandler
396 [logger_simpleExample]
398 handlers=consoleHandler
399 qualname=simpleExample
402 [handler_consoleHandler]
405 formatter=simpleFormatter
408 [formatter_simpleFormatter]
409 format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
412 The output is nearly identical to that of the non-config-file-based example::
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
421 You can see that the config file approach has a few advantages over the Python
422 code approach, mainly separation of configuration and code and the ability of
423 noncoders to easily modify the logging properties.
429 The numeric values of logging levels are given in the following table. These are
430 primarily of interest if you want to define your own levels, and need them to
431 have specific values relative to the predefined levels. If you define a level
432 with the same numeric value, it overwrites the predefined value; the predefined
435 +--------------+---------------+
436 | Level | Numeric value |
437 +==============+===============+
438 | ``CRITICAL`` | 50 |
439 +--------------+---------------+
441 +--------------+---------------+
443 +--------------+---------------+
445 +--------------+---------------+
447 +--------------+---------------+
449 +--------------+---------------+
451 Levels can also be associated with loggers, being set either by the developer or
452 through loading a saved logging configuration. When a logging method is called
453 on a logger, the logger compares its own level with the level associated with
454 the method call. If the logger's level is higher than the method call's, no
455 logging message is actually generated. This is the basic mechanism controlling
456 the verbosity of logging output.
458 Logging messages are encoded as instances of the :class:`LogRecord` class. When
459 a logger decides to actually log an event, a :class:`LogRecord` instance is
460 created from the logging message.
462 Logging messages are subjected to a dispatch mechanism through the use of
463 :dfn:`handlers`, which are instances of subclasses of the :class:`Handler`
464 class. Handlers are responsible for ensuring that a logged message (in the form
465 of a :class:`LogRecord`) ends up in a particular location (or set of locations)
466 which is useful for the target audience for that message (such as end users,
467 support desk staff, system administrators, developers). Handlers are passed
468 :class:`LogRecord` instances intended for particular destinations. Each logger
469 can have zero, one or more handlers associated with it (via the
470 :meth:`addHandler` method of :class:`Logger`). In addition to any handlers
471 directly associated with a logger, *all handlers associated with all ancestors
472 of the logger* are called to dispatch the message.
474 Just as for loggers, handlers can have levels associated with them. A handler's
475 level acts as a filter in the same way as a logger's level does. If a handler
476 decides to actually dispatch an event, the :meth:`emit` method is used to send
477 the message to its destination. Most user-defined subclasses of :class:`Handler`
478 will need to override this :meth:`emit`.
480 In addition to the base :class:`Handler` class, many useful subclasses are
483 #. :class:`StreamHandler` instances send error messages to streams (file-like
486 #. :class:`FileHandler` instances send error messages to disk files.
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`.
492 #. :class:`RotatingFileHandler` instances send error messages to disk files,
493 with support for maximum log file sizes and log file rotation.
495 #. :class:`TimedRotatingFileHandler` instances send error messages to disk files
496 rotating the log file at certain timed intervals.
498 #. :class:`SocketHandler` instances send error messages to TCP/IP sockets.
500 #. :class:`DatagramHandler` instances send error messages to UDP sockets.
502 #. :class:`SMTPHandler` instances send error messages to a designated email
505 #. :class:`SysLogHandler` instances send error messages to a Unix syslog daemon,
506 possibly on a remote machine.
508 #. :class:`NTEventLogHandler` instances send error messages to a Windows
509 NT/2000/XP event log.
511 #. :class:`MemoryHandler` instances send error messages to a buffer in memory,
512 which is flushed whenever specific criteria are met.
514 #. :class:`HTTPHandler` instances send error messages to an HTTP server using
515 either ``GET`` or ``POST`` semantics.
517 The :class:`StreamHandler` and :class:`FileHandler` classes are defined in the
518 core 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.)
522 Logged messages are formatted for presentation through instances of the
523 :class:`Formatter` class. They are initialized with a format string suitable for
524 use with the % operator and a dictionary.
526 For formatting multiple messages in a batch, instances of
527 :class:`BufferingFormatter` can be used. In addition to the format string (which
528 is applied to each message in the batch), there is provision for header and
529 trailer format strings.
531 When filtering based on logger level and/or handler level is not enough,
532 instances of :class:`Filter` can be added to both :class:`Logger` and
533 :class:`Handler` instances (through their :meth:`addFilter` method). Before
534 deciding to process a message further, both loggers and handlers consult all
535 their filters for permission. If any filter returns a false value, the message
536 is not processed further.
538 The basic :class:`Filter` functionality allows filtering by specific logger
539 name. If this feature is used, messages sent to the named logger and its
540 children are allowed through the filter, and all others dropped.
542 In addition to the classes described above, there are a number of module- level
546 .. function:: getLogger([name])
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.
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
558 .. function:: getLoggerClass()
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::
565 class MyLogger(logging.getLoggerClass()):
566 # ... override behaviour here
569 .. function:: debug(msg[, *args[, **kwargs]])
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.)
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.
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::
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)
593 would print something like ::
595 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
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.)
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.
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.
615 .. versionchanged:: 2.5
619 .. function:: info(msg[, *args[, **kwargs]])
621 Logs a message with level :const:`INFO` on the root logger. The arguments are
622 interpreted as for :func:`debug`.
625 .. function:: warning(msg[, *args[, **kwargs]])
627 Logs a message with level :const:`WARNING` on the root logger. The arguments are
628 interpreted as for :func:`debug`.
631 .. function:: error(msg[, *args[, **kwargs]])
633 Logs a message with level :const:`ERROR` on the root logger. The arguments are
634 interpreted as for :func:`debug`.
637 .. function:: critical(msg[, *args[, **kwargs]])
639 Logs a message with level :const:`CRITICAL` on the root logger. The arguments
640 are interpreted as for :func:`debug`.
643 .. function:: exception(msg[, *args])
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.
650 .. function:: log(level, msg[, *args[, **kwargs]])
652 Logs a message with level *level* on the root logger. The other arguments are
653 interpreted as for :func:`debug`.
656 .. function:: disable(lvl)
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.
663 .. function:: addLevelName(lvl, levelName)
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.
673 .. function:: getLevelName(lvl)
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.
684 .. function:: makeLogRecord(attrdict)
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.
692 .. function:: basicConfig([**kwargs])
694 Does basic configuration for the logging system by creating a
695 :class:`StreamHandler` with a default :class:`Formatter` and adding it to the
696 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`,
698 :func:`error` and :func:`critical` will call :func:`basicConfig` automatically
699 if no handlers are defined for the root logger.
701 This function does nothing if the root logger already has handlers configured.
703 .. versionchanged:: 2.4
704 Formerly, :func:`basicConfig` did not take any keyword arguments.
706 The following keyword arguments are supported.
708 +--------------+---------------------------------------------+
709 | Format | Description |
710 +==============+=============================================+
711 | ``filename`` | Specifies that a FileHandler be created, |
712 | | using the specified filename, rather than a |
714 +--------------+---------------------------------------------+
715 | ``filemode`` | Specifies the mode to open the file, if |
716 | | filename is specified (if filemode is |
717 | | unspecified, it defaults to 'a'). |
718 +--------------+---------------------------------------------+
719 | ``format`` | Use the specified format string for the |
721 +--------------+---------------------------------------------+
722 | ``datefmt`` | Use the specified date/time format. |
723 +--------------+---------------------------------------------+
724 | ``level`` | Set the root logger level to the specified |
726 +--------------+---------------------------------------------+
727 | ``stream`` | Use the specified stream to initialize the |
728 | | StreamHandler. Note that this argument is |
729 | | incompatible with 'filename' - if both are |
730 | | present, 'stream' is ignored. |
731 +--------------+---------------------------------------------+
734 .. function:: shutdown()
736 Informs the logging system to perform an orderly shutdown by flushing and
737 closing all handlers. This should be called at application exit and no
738 further use of the logging system should be made after this call.
741 .. function:: setLoggerClass(klass)
743 Tells the logging system to use the class *klass* when instantiating a logger.
744 The class should define :meth:`__init__` such that only a name argument is
745 required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
746 function is typically called before any loggers are instantiated by applications
747 which need to use custom logger behavior.
752 :pep:`282` - A Logging System
753 The proposal which described this feature for inclusion in the Python standard
756 `Original Python logging package <http://www.red-dove.com/python_logging.html>`_
757 This is the original source for the :mod:`logging` package. The version of the
758 package available from this site is suitable for use with Python 1.5.2, 2.1.x
759 and 2.2.x, which do not include the :mod:`logging` package in the standard
766 Loggers have the following attributes and methods. Note that Loggers are never
767 instantiated directly, but always through the module-level function
768 ``logging.getLogger(name)``.
771 .. attribute:: Logger.propagate
773 If this evaluates to false, logging messages are not passed by this logger or by
774 child loggers to higher level (ancestor) loggers. The constructor sets this
778 .. method:: Logger.setLevel(lvl)
780 Sets the threshold for this logger to *lvl*. Logging messages which are less
781 severe than *lvl* will be ignored. When a logger is created, the level is set to
782 :const:`NOTSET` (which causes all messages to be processed when the logger is
783 the root logger, or delegation to the parent when the logger is a non-root
784 logger). Note that the root logger is created with level :const:`WARNING`.
786 The term "delegation to the parent" means that if a logger has a level of
787 NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
788 a level other than NOTSET is found, or the root is reached.
790 If an ancestor is found with a level other than NOTSET, then that ancestor's
791 level is treated as the effective level of the logger where the ancestor search
792 began, and is used to determine how a logging event is handled.
794 If the root is reached, and it has a level of NOTSET, then all messages will be
795 processed. Otherwise, the root's level will be used as the effective level.
798 .. method:: Logger.isEnabledFor(lvl)
800 Indicates if a message of severity *lvl* would be processed by this logger.
801 This method checks first the module-level level set by
802 ``logging.disable(lvl)`` and then the logger's effective level as determined
803 by :meth:`getEffectiveLevel`.
806 .. method:: Logger.getEffectiveLevel()
808 Indicates the effective level for this logger. If a value other than
809 :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
810 the hierarchy is traversed towards the root until a value other than
811 :const:`NOTSET` is found, and that value is returned.
814 .. method:: Logger.debug(msg[, *args[, **kwargs]])
816 Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
817 message format string, and the *args* are the arguments which are merged into
818 *msg* using the string formatting operator. (Note that this means that you can
819 use keywords in the format string, together with a single dictionary argument.)
821 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
822 which, if it does not evaluate as false, causes exception information to be
823 added to the logging message. If an exception tuple (in the format returned by
824 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
825 is called to get the exception information.
827 The other optional keyword argument is *extra* which can be used to pass a
828 dictionary which is used to populate the __dict__ of the LogRecord created for
829 the logging event with user-defined attributes. These custom attributes can then
830 be used as you like. For example, they could be incorporated into logged
831 messages. For example::
833 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
834 logging.basicConfig(format=FORMAT)
835 d = { 'clientip' : '192.168.0.1', 'user' : 'fbloggs' }
836 logger = logging.getLogger("tcpserver")
837 logger.warning("Protocol problem: %s", "connection reset", extra=d)
839 would print something like ::
841 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
843 The keys in the dictionary passed in *extra* should not clash with the keys used
844 by the logging system. (See the :class:`Formatter` documentation for more
845 information on which keys are used by the logging system.)
847 If you choose to use these attributes in logged messages, you need to exercise
848 some care. In the above example, for instance, the :class:`Formatter` has been
849 set up with a format string which expects 'clientip' and 'user' in the attribute
850 dictionary of the LogRecord. If these are missing, the message will not be
851 logged because a string formatting exception will occur. So in this case, you
852 always need to pass the *extra* dictionary with these keys.
854 While this might be annoying, this feature is intended for use in specialized
855 circumstances, such as multi-threaded servers where the same code executes in
856 many contexts, and interesting conditions which arise are dependent on this
857 context (such as remote client IP address and authenticated user name, in the
858 above example). In such circumstances, it is likely that specialized
859 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
861 .. versionchanged:: 2.5
865 .. method:: Logger.info(msg[, *args[, **kwargs]])
867 Logs a message with level :const:`INFO` on this logger. The arguments are
868 interpreted as for :meth:`debug`.
871 .. method:: Logger.warning(msg[, *args[, **kwargs]])
873 Logs a message with level :const:`WARNING` on this logger. The arguments are
874 interpreted as for :meth:`debug`.
877 .. method:: Logger.error(msg[, *args[, **kwargs]])
879 Logs a message with level :const:`ERROR` on this logger. The arguments are
880 interpreted as for :meth:`debug`.
883 .. method:: Logger.critical(msg[, *args[, **kwargs]])
885 Logs a message with level :const:`CRITICAL` on this logger. The arguments are
886 interpreted as for :meth:`debug`.
889 .. method:: Logger.log(lvl, msg[, *args[, **kwargs]])
891 Logs a message with integer level *lvl* on this logger. The other arguments are
892 interpreted as for :meth:`debug`.
895 .. method:: Logger.exception(msg[, *args])
897 Logs a message with level :const:`ERROR` on this logger. The arguments are
898 interpreted as for :meth:`debug`. Exception info is added to the logging
899 message. This method should only be called from an exception handler.
902 .. method:: Logger.addFilter(filt)
904 Adds the specified filter *filt* to this logger.
907 .. method:: Logger.removeFilter(filt)
909 Removes the specified filter *filt* from this logger.
912 .. method:: Logger.filter(record)
914 Applies this logger's filters to the record and returns a true value if the
915 record is to be processed.
918 .. method:: Logger.addHandler(hdlr)
920 Adds the specified handler *hdlr* to this logger.
923 .. method:: Logger.removeHandler(hdlr)
925 Removes the specified handler *hdlr* from this logger.
928 .. method:: Logger.findCaller()
930 Finds the caller's source filename and line number. Returns the filename, line
931 number and function name as a 3-element tuple.
933 .. versionchanged:: 2.4
934 The function name was added. In earlier versions, the filename and line number
935 were returned as a 2-element tuple..
938 .. method:: Logger.handle(record)
940 Handles a record by passing it to all handlers associated with this logger and
941 its ancestors (until a false value of *propagate* is found). This method is used
942 for unpickled records received from a socket, as well as those created locally.
943 Logger-level filtering is applied using :meth:`filter`.
946 .. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info [, func, extra])
948 This is a factory method which can be overridden in subclasses to create
949 specialized :class:`LogRecord` instances.
951 .. versionchanged:: 2.5
952 *func* and *extra* were added.
960 .. versionchanged:: 2.4
961 formerly :func:`basicConfig` did not take any keyword arguments.
963 The :mod:`logging` package provides a lot of flexibility, and its configuration
964 can appear daunting. This section demonstrates that simple use of the logging
967 The simplest example shows logging to the console::
971 logging.debug('A debug message')
972 logging.info('Some information')
973 logging.warning('A shot across the bows')
975 If you run the above script, you'll see this::
977 WARNING:root:A shot across the bows
979 Because no particular logger was specified, the system used the root logger. The
980 debug and info messages didn't appear because by default, the root logger is
981 configured to only handle messages with a severity of WARNING or above. The
982 message format is also a configuration default, as is the output destination of
983 the messages - ``sys.stderr``. The severity level, the message format and
984 destination can be easily changed, as shown in the example below::
988 logging.basicConfig(level=logging.DEBUG,
989 format='%(asctime)s %(levelname)s %(message)s',
990 filename='/tmp/myapp.log',
992 logging.debug('A debug message')
993 logging.info('Some information')
994 logging.warning('A shot across the bows')
996 The :meth:`basicConfig` method is used to change the configuration defaults,
997 which results in output (written to ``/tmp/myapp.log``) which should look
998 something like the following::
1000 2004-07-02 13:00:08,743 DEBUG A debug message
1001 2004-07-02 13:00:08,743 INFO Some information
1002 2004-07-02 13:00:08,743 WARNING A shot across the bows
1004 This time, all messages with a severity of DEBUG or above were handled, and the
1005 format of the messages was also changed, and output went to the specified file
1006 rather than the console.
1008 Formatting uses standard Python string formatting - see section
1009 :ref:`string-formatting`. The format string takes the following common
1010 specifiers. For a complete list of specifiers, consult the :class:`Formatter`
1013 +-------------------+-----------------------------------------------+
1014 | Format | Description |
1015 +===================+===============================================+
1016 | ``%(name)s`` | Name of the logger (logging channel). |
1017 +-------------------+-----------------------------------------------+
1018 | ``%(levelname)s`` | Text logging level for the message |
1019 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1020 | | ``'ERROR'``, ``'CRITICAL'``). |
1021 +-------------------+-----------------------------------------------+
1022 | ``%(asctime)s`` | Human-readable time when the |
1023 | | :class:`LogRecord` was created. By default |
1024 | | this is of the form "2003-07-08 16:49:45,896" |
1025 | | (the numbers after the comma are millisecond |
1026 | | portion of the time). |
1027 +-------------------+-----------------------------------------------+
1028 | ``%(message)s`` | The logged message. |
1029 +-------------------+-----------------------------------------------+
1031 To change the date/time format, you can pass an additional keyword parameter,
1032 *datefmt*, as in the following::
1036 logging.basicConfig(level=logging.DEBUG,
1037 format='%(asctime)s %(levelname)-8s %(message)s',
1038 datefmt='%a, %d %b %Y %H:%M:%S',
1039 filename='/temp/myapp.log',
1041 logging.debug('A debug message')
1042 logging.info('Some information')
1043 logging.warning('A shot across the bows')
1045 which would result in output like ::
1047 Fri, 02 Jul 2004 13:06:18 DEBUG A debug message
1048 Fri, 02 Jul 2004 13:06:18 INFO Some information
1049 Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows
1051 The date format string follows the requirements of :func:`strftime` - see the
1052 documentation for the :mod:`time` module.
1054 If, instead of sending logging output to the console or a file, you'd rather use
1055 a file-like object which you have created separately, you can pass it to
1056 :func:`basicConfig` using the *stream* keyword argument. Note that if both
1057 *stream* and *filename* keyword arguments are passed, the *stream* argument is
1060 Of course, you can put variable information in your output. To do this, simply
1061 have the message be a format string and pass in additional arguments containing
1062 the variable information, as in the following example::
1066 logging.basicConfig(level=logging.DEBUG,
1067 format='%(asctime)s %(levelname)-8s %(message)s',
1068 datefmt='%a, %d %b %Y %H:%M:%S',
1069 filename='/temp/myapp.log',
1071 logging.error('Pack my box with %d dozen %s', 5, 'liquor jugs')
1073 which would result in ::
1075 Wed, 21 Jul 2004 15:35:16 ERROR Pack my box with 5 dozen liquor jugs
1078 .. _multiple-destinations:
1080 Logging to multiple destinations
1081 --------------------------------
1083 Let's say you want to log to console and file with different message formats and
1084 in differing circumstances. Say you want to log messages with levels of DEBUG
1085 and higher to file, and those messages at level INFO and higher to the console.
1086 Let's also assume that the file should contain timestamps, but the console
1087 messages should not. Here's how you can achieve this::
1091 # set up logging to file - see previous section for more details
1092 logging.basicConfig(level=logging.DEBUG,
1093 format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
1094 datefmt='%m-%d %H:%M',
1095 filename='/temp/myapp.log',
1097 # define a Handler which writes INFO messages or higher to the sys.stderr
1098 console = logging.StreamHandler()
1099 console.setLevel(logging.INFO)
1100 # set a format which is simpler for console use
1101 formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
1102 # tell the handler to use this format
1103 console.setFormatter(formatter)
1104 # add the handler to the root logger
1105 logging.getLogger('').addHandler(console)
1107 # Now, we can log to the root logger, or any other logger. First the root...
1108 logging.info('Jackdaws love my big sphinx of quartz.')
1110 # Now, define a couple of other loggers which might represent areas in your
1113 logger1 = logging.getLogger('myapp.area1')
1114 logger2 = logging.getLogger('myapp.area2')
1116 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1117 logger1.info('How quickly daft jumping zebras vex.')
1118 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1119 logger2.error('The five boxing wizards jump quickly.')
1121 When you run this, on the console you will see ::
1123 root : INFO Jackdaws love my big sphinx of quartz.
1124 myapp.area1 : INFO How quickly daft jumping zebras vex.
1125 myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
1126 myapp.area2 : ERROR The five boxing wizards jump quickly.
1128 and in the file you will see something like ::
1130 10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
1131 10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1132 10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
1133 10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1134 10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
1136 As you can see, the DEBUG message only shows up in the file. The other messages
1137 are sent to both destinations.
1139 This example uses console and file handlers, but you can use any number and
1140 combination of handlers you choose.
1145 Adding contextual information to your logging output
1146 ----------------------------------------------------
1148 Sometimes you want logging output to contain contextual information in
1149 addition to the parameters passed to the logging call. For example, in a
1150 networked application, it may be desirable to log client-specific information
1151 in the log (e.g. remote client's username, or IP address). Although you could
1152 use the *extra* parameter to achieve this, it's not always convenient to pass
1153 the information in this way. While it might be tempting to create
1154 :class:`Logger` instances on a per-connection basis, this is not a good idea
1155 because these instances are not garbage collected. While this is not a problem
1156 in practice, when the number of :class:`Logger` instances is dependent on the
1157 level of granularity you want to use in logging an application, it could
1158 be hard to manage if the number of :class:`Logger` instances becomes
1159 effectively unbounded.
1161 An easy way in which you can pass contextual information to be output along
1162 with logging event information is to use the :class:`LoggerAdapter` class.
1163 This class is designed to look like a :class:`Logger`, so that you can call
1164 :meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
1165 :meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
1166 same signatures as their counterparts in :class:`Logger`, so you can use the
1167 two types of instances interchangeably.
1169 When you create an instance of :class:`LoggerAdapter`, you pass it a
1170 :class:`Logger` instance and a dict-like object which contains your contextual
1171 information. When you call one of the logging methods on an instance of
1172 :class:`LoggerAdapter`, it delegates the call to the underlying instance of
1173 :class:`Logger` passed to its constructor, and arranges to pass the contextual
1174 information in the delegated call. Here's a snippet from the code of
1175 :class:`LoggerAdapter`::
1177 def debug(self, msg, *args, **kwargs):
1179 Delegate a debug call to the underlying logger, after adding
1180 contextual information from this adapter instance.
1182 msg, kwargs = self.process(msg, kwargs)
1183 self.logger.debug(msg, *args, **kwargs)
1185 The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
1186 information is added to the logging output. It's passed the message and
1187 keyword arguments of the logging call, and it passes back (potentially)
1188 modified versions of these to use in the call to the underlying logger. The
1189 default implementation of this method leaves the message alone, but inserts
1190 an "extra" key in the keyword argument whose value is the dict-like object
1191 passed to the constructor. Of course, if you had passed an "extra" keyword
1192 argument in the call to the adapter, it will be silently overwritten.
1194 The advantage of using "extra" is that the values in the dict-like object are
1195 merged into the :class:`LogRecord` instance's __dict__, allowing you to use
1196 customized strings with your :class:`Formatter` instances which know about
1197 the keys of the dict-like object. If you need a different method, e.g. if you
1198 want to prepend or append the contextual information to the message string,
1199 you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
1200 to do what you need. Here's an example script which uses this class, which
1201 also illustrates what dict-like behaviour is needed from an arbitrary
1202 "dict-like" object for use in the constructor::
1208 An example class which shows how an arbitrary class can be used as
1209 the 'extra' context information repository passed to a LoggerAdapter.
1212 def __getitem__(self, name):
1214 To allow this instance to look like a dict.
1216 from random import choice
1218 result = choice(["127.0.0.1", "192.168.0.1"])
1219 elif name == "user":
1220 result = choice(["jim", "fred", "sheila"])
1222 result = self.__dict__.get(name, "?")
1227 To allow iteration over keys, which will be merged into
1228 the LogRecord dict before formatting and output.
1230 keys = ["ip", "user"]
1231 keys.extend(self.__dict__.keys())
1232 return keys.__iter__()
1234 if __name__ == "__main__":
1235 from random import choice
1236 levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
1237 a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"),
1238 { "ip" : "123.231.231.123", "user" : "sheila" })
1239 logging.basicConfig(level=logging.DEBUG,
1240 format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s")
1241 a1.debug("A debug message")
1242 a1.info("An info message with %s", "some parameters")
1243 a2 = logging.LoggerAdapter(logging.getLogger("d.e.f"), ConnInfo())
1245 lvl = choice(levels)
1246 lvlname = logging.getLevelName(lvl)
1247 a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters")
1249 When this script is run, the output should look something like this::
1251 2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
1252 2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
1253 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
1254 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
1255 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
1256 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
1257 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
1258 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
1259 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
1260 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
1261 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
1262 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
1264 .. versionadded:: 2.6
1266 The :class:`LoggerAdapter` class was not present in previous versions.
1269 .. _network-logging:
1271 Sending and receiving logging events across a network
1272 -----------------------------------------------------
1274 Let's say you want to send logging events across a network, and handle them at
1275 the receiving end. A simple way of doing this is attaching a
1276 :class:`SocketHandler` instance to the root logger at the sending end::
1278 import logging, logging.handlers
1280 rootLogger = logging.getLogger('')
1281 rootLogger.setLevel(logging.DEBUG)
1282 socketHandler = logging.handlers.SocketHandler('localhost',
1283 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1284 # don't bother with a formatter, since a socket handler sends the event as
1285 # an unformatted pickle
1286 rootLogger.addHandler(socketHandler)
1288 # Now, we can log to the root logger, or any other logger. First the root...
1289 logging.info('Jackdaws love my big sphinx of quartz.')
1291 # Now, define a couple of other loggers which might represent areas in your
1294 logger1 = logging.getLogger('myapp.area1')
1295 logger2 = logging.getLogger('myapp.area2')
1297 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1298 logger1.info('How quickly daft jumping zebras vex.')
1299 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1300 logger2.error('The five boxing wizards jump quickly.')
1302 At the receiving end, you can set up a receiver using the :mod:`socketserver`
1303 module. Here is a basic working example::
1307 import logging.handlers
1312 class LogRecordStreamHandler(socketserver.StreamRequestHandler):
1313 """Handler for a streaming logging request.
1315 This basically logs the record using whatever logging policy is
1321 Handle multiple requests - each expected to be a 4-byte length,
1322 followed by the LogRecord in pickle format. Logs the record
1323 according to whatever policy is configured locally.
1326 chunk = self.connection.recv(4)
1329 slen = struct.unpack(">L", chunk)[0]
1330 chunk = self.connection.recv(slen)
1331 while len(chunk) < slen:
1332 chunk = chunk + self.connection.recv(slen - len(chunk))
1333 obj = self.unPickle(chunk)
1334 record = logging.makeLogRecord(obj)
1335 self.handleLogRecord(record)
1337 def unPickle(self, data):
1338 return cPickle.loads(data)
1340 def handleLogRecord(self, record):
1341 # if a name is specified, we use the named logger rather than the one
1342 # implied by the record.
1343 if self.server.logname is not None:
1344 name = self.server.logname
1347 logger = logging.getLogger(name)
1348 # N.B. EVERY record gets logged. This is because Logger.handle
1349 # is normally called AFTER logger-level filtering. If you want
1350 # to do filtering, do it at the client end to save wasting
1351 # cycles and network bandwidth!
1352 logger.handle(record)
1354 class LogRecordSocketReceiver(socketserver.ThreadingTCPServer):
1355 """simple TCP socket-based logging receiver suitable for testing.
1358 allow_reuse_address = 1
1360 def __init__(self, host='localhost',
1361 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1362 handler=LogRecordStreamHandler):
1363 socketserver.ThreadingTCPServer.__init__(self, (host, port), handler)
1368 def serve_until_stopped(self):
1372 rd, wr, ex = select.select([self.socket.fileno()],
1376 self.handle_request()
1380 logging.basicConfig(
1381 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1382 tcpserver = LogRecordSocketReceiver()
1383 print "About to start TCP server..."
1384 tcpserver.serve_until_stopped()
1386 if __name__ == "__main__":
1389 First run the server, and then the client. On the client side, nothing is
1390 printed on the console; on the server side, you should see something like::
1392 About to start TCP server...
1393 59 root INFO Jackdaws love my big sphinx of quartz.
1394 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1395 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1396 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1397 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1403 Handlers have the following attributes and methods. Note that :class:`Handler`
1404 is never instantiated directly; this class acts as a base for more useful
1405 subclasses. However, the :meth:`__init__` method in subclasses needs to call
1406 :meth:`Handler.__init__`.
1409 .. method:: Handler.__init__(level=NOTSET)
1411 Initializes the :class:`Handler` instance by setting its level, setting the list
1412 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1413 serializing access to an I/O mechanism.
1416 .. method:: Handler.createLock()
1418 Initializes a thread lock which can be used to serialize access to underlying
1419 I/O functionality which may not be threadsafe.
1422 .. method:: Handler.acquire()
1424 Acquires the thread lock created with :meth:`createLock`.
1427 .. method:: Handler.release()
1429 Releases the thread lock acquired with :meth:`acquire`.
1432 .. method:: Handler.setLevel(lvl)
1434 Sets the threshold for this handler to *lvl*. Logging messages which are less
1435 severe than *lvl* will be ignored. When a handler is created, the level is set
1436 to :const:`NOTSET` (which causes all messages to be processed).
1439 .. method:: Handler.setFormatter(form)
1441 Sets the :class:`Formatter` for this handler to *form*.
1444 .. method:: Handler.addFilter(filt)
1446 Adds the specified filter *filt* to this handler.
1449 .. method:: Handler.removeFilter(filt)
1451 Removes the specified filter *filt* from this handler.
1454 .. method:: Handler.filter(record)
1456 Applies this handler's filters to the record and returns a true value if the
1457 record is to be processed.
1460 .. method:: Handler.flush()
1462 Ensure all logging output has been flushed. This version does nothing and is
1463 intended to be implemented by subclasses.
1466 .. method:: Handler.close()
1468 Tidy up any resources used by the handler. This version does nothing and is
1469 intended to be implemented by subclasses.
1472 .. method:: Handler.handle(record)
1474 Conditionally emits the specified logging record, depending on filters which may
1475 have been added to the handler. Wraps the actual emission of the record with
1476 acquisition/release of the I/O thread lock.
1479 .. method:: Handler.handleError(record)
1481 This method should be called from handlers when an exception is encountered
1482 during an :meth:`emit` call. By default it does nothing, which means that
1483 exceptions get silently ignored. This is what is mostly wanted for a logging
1484 system - most users will not care about errors in the logging system, they are
1485 more interested in application errors. You could, however, replace this with a
1486 custom handler if you wish. The specified record is the one which was being
1487 processed when the exception occurred.
1490 .. method:: Handler.format(record)
1492 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1493 default formatter for the module.
1496 .. method:: Handler.emit(record)
1498 Do whatever it takes to actually log the specified logging record. This version
1499 is intended to be implemented by subclasses and so raises a
1500 :exc:`NotImplementedError`.
1506 The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1507 sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1508 file-like object (or, more precisely, any object which supports :meth:`write`
1509 and :meth:`flush` methods).
1512 .. class:: StreamHandler([strm])
1514 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1515 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1519 .. method:: emit(record)
1521 If a formatter is specified, it is used to format the record. The record
1522 is then written to the stream with a trailing newline. If exception
1523 information is present, it is formatted using
1524 :func:`traceback.print_exception` and appended to the stream.
1529 Flushes the stream by calling its :meth:`flush` method. Note that the
1530 :meth:`close` method is inherited from :class:`Handler` and so does
1531 nothing, so an explicit :meth:`flush` call may be needed at times.
1537 The :class:`FileHandler` class, located in the core :mod:`logging` package,
1538 sends logging output to a disk file. It inherits the output functionality from
1539 :class:`StreamHandler`.
1542 .. class:: FileHandler(filename[, mode[, encoding[, delay]]])
1544 Returns a new instance of the :class:`FileHandler` class. The specified file is
1545 opened and used as the stream for logging. If *mode* is not specified,
1546 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1547 with that encoding. If *delay* is true, then file opening is deferred until the
1548 first call to :meth:`emit`. By default, the file grows indefinitely.
1556 .. method:: emit(record)
1558 Outputs the record to the file.
1564 .. versionadded:: 2.6
1566 The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1567 module, is a :class:`FileHandler` which watches the file it is logging to. If
1568 the file changes, it is closed and reopened using the file name.
1570 A file change can happen because of usage of programs such as *newsyslog* and
1571 *logrotate* which perform log file rotation. This handler, intended for use
1572 under Unix/Linux, watches the file to see if it has changed since the last emit.
1573 (A file is deemed to have changed if its device or inode have changed.) If the
1574 file has changed, the old file stream is closed, and the file opened to get a
1577 This handler is not appropriate for use under Windows, because under Windows
1578 open log files cannot be moved or renamed - logging opens the files with
1579 exclusive locks - and so there is no need for such a handler. Furthermore,
1580 *ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1584 .. class:: WatchedFileHandler(filename[,mode[, encoding[, delay]]])
1586 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1587 file is opened and used as the stream for logging. If *mode* is not specified,
1588 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1589 with that encoding. If *delay* is true, then file opening is deferred until the
1590 first call to :meth:`emit`. By default, the file grows indefinitely.
1593 .. method:: emit(record)
1595 Outputs the record to the file, but first checks to see if the file has
1596 changed. If it has, the existing stream is flushed and closed and the
1597 file opened again, before outputting the record to the file.
1603 The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1604 module, supports rotation of disk log files.
1607 .. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount[, encoding[, delay]]]]])
1609 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1610 file is opened and used as the stream for logging. If *mode* is not specified,
1611 ``'a'`` is used. If *encoding* is not *None*, it is used to open the file
1612 with that encoding. If *delay* is true, then file opening is deferred until the
1613 first call to :meth:`emit`. By default, the file grows indefinitely.
1615 You can use the *maxBytes* and *backupCount* values to allow the file to
1616 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1617 the file is closed and a new file is silently opened for output. Rollover occurs
1618 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1619 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1620 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1621 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1622 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1623 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1624 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1625 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1626 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1629 .. method:: doRollover()
1631 Does a rollover, as described above.
1634 .. method:: emit(record)
1636 Outputs the record to the file, catering for rollover as described
1640 TimedRotatingFileHandler
1641 ^^^^^^^^^^^^^^^^^^^^^^^^
1643 The :class:`TimedRotatingFileHandler` class, located in the
1644 :mod:`logging.handlers` module, supports rotation of disk log files at certain
1648 .. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount[, encoding[, delay]]]]])
1650 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1651 specified file is opened and used as the stream for logging. On rotating it also
1652 sets the filename suffix. Rotating happens based on the product of *when* and
1655 You can use the *when* to specify the type of *interval*. The list of possible
1656 values is, note that they are not case sensitive:
1658 +----------------+-----------------------+
1659 | Value | Type of interval |
1660 +================+=======================+
1661 | ``'S'`` | Seconds |
1662 +----------------+-----------------------+
1663 | ``'M'`` | Minutes |
1664 +----------------+-----------------------+
1666 +----------------+-----------------------+
1668 +----------------+-----------------------+
1669 | ``'W'`` | Week day (0=Monday) |
1670 +----------------+-----------------------+
1671 | ``'midnight'`` | Roll over at midnight |
1672 +----------------+-----------------------+
1674 The system will save old log files by appending extensions to the filename.
1675 The extensions are date-and-time based, using the strftime format
1676 ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on the
1677 rollover interval. If *backupCount* is nonzero, at most *backupCount* files
1678 will be kept, and if more would be created when rollover occurs, the oldest
1679 one is deleted. The deletion logic uses the interval to determine which
1680 files to delete, so changing the interval may leave old files lying around.
1683 .. method:: doRollover()
1685 Does a rollover, as described above.
1688 .. method:: emit(record)
1690 Outputs the record to the file, catering for rollover as described above.
1696 The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1697 sends logging output to a network socket. The base class uses a TCP socket.
1700 .. class:: SocketHandler(host, port)
1702 Returns a new instance of the :class:`SocketHandler` class intended to
1703 communicate with a remote machine whose address is given by *host* and *port*.
1713 Pickles the record's attribute dictionary and writes it to the socket in
1714 binary format. If there is an error with the socket, silently drops the
1715 packet. If the connection was previously lost, re-establishes the
1716 connection. To unpickle the record at the receiving end into a
1717 :class:`LogRecord`, use the :func:`makeLogRecord` function.
1720 .. method:: handleError()
1722 Handles an error which has occurred during :meth:`emit`. The most likely
1723 cause is a lost connection. Closes the socket so that we can retry on the
1727 .. method:: makeSocket()
1729 This is a factory method which allows subclasses to define the precise
1730 type of socket they want. The default implementation creates a TCP socket
1731 (:const:`socket.SOCK_STREAM`).
1734 .. method:: makePickle(record)
1736 Pickles the record's attribute dictionary in binary format with a length
1737 prefix, and returns it ready for transmission across the socket.
1740 .. method:: send(packet)
1742 Send a pickled string *packet* to the socket. This function allows for
1743 partial sends which can happen when the network is busy.
1749 The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1750 module, inherits from :class:`SocketHandler` to support sending logging messages
1754 .. class:: DatagramHandler(host, port)
1756 Returns a new instance of the :class:`DatagramHandler` class intended to
1757 communicate with a remote machine whose address is given by *host* and *port*.
1762 Pickles the record's attribute dictionary and writes it to the socket in
1763 binary format. If there is an error with the socket, silently drops the
1764 packet. To unpickle the record at the receiving end into a
1765 :class:`LogRecord`, use the :func:`makeLogRecord` function.
1768 .. method:: makeSocket()
1770 The factory method of :class:`SocketHandler` is here overridden to create
1771 a UDP socket (:const:`socket.SOCK_DGRAM`).
1776 Send a pickled string to a socket.
1782 The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1783 supports sending logging messages to a remote or local Unix syslog.
1786 .. class:: SysLogHandler([address[, facility]])
1788 Returns a new instance of the :class:`SysLogHandler` class intended to
1789 communicate with a remote Unix machine whose address is given by *address* in
1790 the form of a ``(host, port)`` tuple. If *address* is not specified,
1791 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1792 alternative to providing a ``(host, port)`` tuple is providing an address as a
1793 string, for example "/dev/log". In this case, a Unix domain socket is used to
1794 send the message to the syslog. If *facility* is not specified,
1795 :const:`LOG_USER` is used.
1800 Closes the socket to the remote host.
1803 .. method:: emit(record)
1805 The record is formatted, and then sent to the syslog server. If exception
1806 information is present, it is *not* sent to the server.
1809 .. method:: encodePriority(facility, priority)
1811 Encodes the facility and priority into an integer. You can pass in strings
1812 or integers - if strings are passed, internal mapping dictionaries are
1813 used to convert them to integers.
1819 The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1820 module, supports sending logging messages to a local Windows NT, Windows 2000 or
1821 Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1822 extensions for Python installed.
1825 .. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1827 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1828 used to define the application name as it appears in the event log. An
1829 appropriate registry entry is created using this name. The *dllname* should give
1830 the fully qualified pathname of a .dll or .exe which contains message
1831 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1832 - this is installed with the Win32 extensions and contains some basic
1833 placeholder message definitions. Note that use of these placeholders will make
1834 your event logs big, as the entire message source is held in the log. If you
1835 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1836 contains the message definitions you want to use in the event log). The
1837 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1838 defaults to ``'Application'``.
1843 At this point, you can remove the application name from the registry as a
1844 source of event log entries. However, if you do this, you will not be able
1845 to see the events as you intended in the Event Log Viewer - it needs to be
1846 able to access the registry to get the .dll name. The current version does
1847 not do this (in fact it doesn't do anything).
1850 .. method:: emit(record)
1852 Determines the message ID, event category and event type, and then logs
1853 the message in the NT event log.
1856 .. method:: getEventCategory(record)
1858 Returns the event category for the record. Override this if you want to
1859 specify your own categories. This version returns 0.
1862 .. method:: getEventType(record)
1864 Returns the event type for the record. Override this if you want to
1865 specify your own types. This version does a mapping using the handler's
1866 typemap attribute, which is set up in :meth:`__init__` to a dictionary
1867 which contains mappings for :const:`DEBUG`, :const:`INFO`,
1868 :const:`WARNING`, :const:`ERROR` and :const:`CRITICAL`. If you are using
1869 your own levels, you will either need to override this method or place a
1870 suitable dictionary in the handler's *typemap* attribute.
1873 .. method:: getMessageID(record)
1875 Returns the message ID for the record. If you are using your own messages,
1876 you could do this by having the *msg* passed to the logger being an ID
1877 rather than a format string. Then, in here, you could use a dictionary
1878 lookup to get the message ID. This version returns 1, which is the base
1879 message ID in :file:`win32service.pyd`.
1885 The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1886 supports sending logging messages to an email address via SMTP.
1889 .. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1891 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1892 initialized with the from and to addresses and subject line of the email. The
1893 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1894 the (host, port) tuple format for the *mailhost* argument. If you use a string,
1895 the standard SMTP port is used. If your SMTP server requires authentication, you
1896 can specify a (username, password) tuple for the *credentials* argument.
1898 .. versionchanged:: 2.6
1899 *credentials* was added.
1902 .. method:: emit(record)
1904 Formats the record and sends it to the specified addressees.
1907 .. method:: getSubject(record)
1909 If you want to specify a subject line which is record-dependent, override
1916 The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
1917 supports buffering of logging records in memory, periodically flushing them to a
1918 :dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
1919 event of a certain severity or greater is seen.
1921 :class:`MemoryHandler` is a subclass of the more general
1922 :class:`BufferingHandler`, which is an abstract class. This buffers logging
1923 records in memory. Whenever each record is added to the buffer, a check is made
1924 by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
1925 should, then :meth:`flush` is expected to do the needful.
1928 .. class:: BufferingHandler(capacity)
1930 Initializes the handler with a buffer of the specified capacity.
1933 .. method:: emit(record)
1935 Appends the record to the buffer. If :meth:`shouldFlush` returns true,
1936 calls :meth:`flush` to process the buffer.
1941 You can override this to implement custom flushing behavior. This version
1942 just zaps the buffer to empty.
1945 .. method:: shouldFlush(record)
1947 Returns true if the buffer is up to capacity. This method can be
1948 overridden to implement custom flushing strategies.
1951 .. class:: MemoryHandler(capacity[, flushLevel [, target]])
1953 Returns a new instance of the :class:`MemoryHandler` class. The instance is
1954 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
1955 :const:`ERROR` is used. If no *target* is specified, the target will need to be
1956 set using :meth:`setTarget` before this handler does anything useful.
1961 Calls :meth:`flush`, sets the target to :const:`None` and clears the
1967 For a :class:`MemoryHandler`, flushing means just sending the buffered
1968 records to the target, if there is one. Override if you want different
1972 .. method:: setTarget(target)
1974 Sets the target handler for this handler.
1977 .. method:: shouldFlush(record)
1979 Checks for buffer full or a record at the *flushLevel* or higher.
1985 The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
1986 supports sending logging messages to a Web server, using either ``GET`` or
1990 .. class:: HTTPHandler(host, url[, method])
1992 Returns a new instance of the :class:`HTTPHandler` class. The instance is
1993 initialized with a host address, url and HTTP method. The *host* can be of the
1994 form ``host:port``, should you need to use a specific port number. If no
1995 *method* is specified, ``GET`` is used.
1998 .. method:: emit(record)
2000 Sends the record to the Web server as an URL-encoded dictionary.
2003 .. _formatter-objects:
2008 :class:`Formatter`\ s have the following attributes and methods. They are
2009 responsible for converting a :class:`LogRecord` to (usually) a string which can
2010 be interpreted by either a human or an external system. The base
2011 :class:`Formatter` allows a formatting string to be specified. If none is
2012 supplied, the default value of ``'%(message)s'`` is used.
2014 A Formatter can be initialized with a format string which makes use of knowledge
2015 of the :class:`LogRecord` attributes - such as the default value mentioned above
2016 making use of the fact that the user's message and arguments are pre-formatted
2017 into a :class:`LogRecord`'s *message* attribute. This format string contains
2018 standard python %-style mapping keys. See section :ref:`string-formatting`
2019 for more information on string formatting.
2021 Currently, the useful mapping keys in a :class:`LogRecord` are:
2023 +-------------------------+-----------------------------------------------+
2024 | Format | Description |
2025 +=========================+===============================================+
2026 | ``%(name)s`` | Name of the logger (logging channel). |
2027 +-------------------------+-----------------------------------------------+
2028 | ``%(levelno)s`` | Numeric logging level for the message |
2029 | | (:const:`DEBUG`, :const:`INFO`, |
2030 | | :const:`WARNING`, :const:`ERROR`, |
2031 | | :const:`CRITICAL`). |
2032 +-------------------------+-----------------------------------------------+
2033 | ``%(levelname)s`` | Text logging level for the message |
2034 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
2035 | | ``'ERROR'``, ``'CRITICAL'``). |
2036 +-------------------------+-----------------------------------------------+
2037 | ``%(pathname)s`` | Full pathname of the source file where the |
2038 | | logging call was issued (if available). |
2039 +-------------------------+-----------------------------------------------+
2040 | ``%(filename)s`` | Filename portion of pathname. |
2041 +-------------------------+-----------------------------------------------+
2042 | ``%(module)s`` | Module (name portion of filename). |
2043 +-------------------------+-----------------------------------------------+
2044 | ``%(funcName)s`` | Name of function containing the logging call. |
2045 +-------------------------+-----------------------------------------------+
2046 | ``%(lineno)d`` | Source line number where the logging call was |
2047 | | issued (if available). |
2048 +-------------------------+-----------------------------------------------+
2049 | ``%(created)f`` | Time when the :class:`LogRecord` was created |
2050 | | (as returned by :func:`time.time`). |
2051 +-------------------------+-----------------------------------------------+
2052 | ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
2053 | | created, relative to the time the logging |
2054 | | module was loaded. |
2055 +-------------------------+-----------------------------------------------+
2056 | ``%(asctime)s`` | Human-readable time when the |
2057 | | :class:`LogRecord` was created. By default |
2058 | | this is of the form "2003-07-08 16:49:45,896" |
2059 | | (the numbers after the comma are millisecond |
2060 | | portion of the time). |
2061 +-------------------------+-----------------------------------------------+
2062 | ``%(msecs)d`` | Millisecond portion of the time when the |
2063 | | :class:`LogRecord` was created. |
2064 +-------------------------+-----------------------------------------------+
2065 | ``%(thread)d`` | Thread ID (if available). |
2066 +-------------------------+-----------------------------------------------+
2067 | ``%(threadName)s`` | Thread name (if available). |
2068 +-------------------------+-----------------------------------------------+
2069 | ``%(process)d`` | Process ID (if available). |
2070 +-------------------------+-----------------------------------------------+
2071 | ``%(message)s`` | The logged message, computed as ``msg % |
2073 +-------------------------+-----------------------------------------------+
2075 .. versionchanged:: 2.5
2076 *funcName* was added.
2079 .. class:: Formatter([fmt[, datefmt]])
2081 Returns a new instance of the :class:`Formatter` class. The instance is
2082 initialized with a format string for the message as a whole, as well as a format
2083 string for the date/time portion of a message. If no *fmt* is specified,
2084 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
2088 .. method:: format(record)
2090 The record's attribute dictionary is used as the operand to a string
2091 formatting operation. Returns the resulting string. Before formatting the
2092 dictionary, a couple of preparatory steps are carried out. The *message*
2093 attribute of the record is computed using *msg* % *args*. If the
2094 formatting string contains ``'(asctime)'``, :meth:`formatTime` is called
2095 to format the event time. If there is exception information, it is
2096 formatted using :meth:`formatException` and appended to the message. Note
2097 that the formatted exception information is cached in attribute
2098 *exc_text*. This is useful because the exception information can be
2099 pickled and sent across the wire, but you should be careful if you have
2100 more than one :class:`Formatter` subclass which customizes the formatting
2101 of exception information. In this case, you will have to clear the cached
2102 value after a formatter has done its formatting, so that the next
2103 formatter to handle the event doesn't use the cached value but
2104 recalculates it afresh.
2107 .. method:: formatTime(record[, datefmt])
2109 This method should be called from :meth:`format` by a formatter which
2110 wants to make use of a formatted time. This method can be overridden in
2111 formatters to provide for any specific requirement, but the basic behavior
2112 is as follows: if *datefmt* (a string) is specified, it is used with
2113 :func:`time.strftime` to format the creation time of the
2114 record. Otherwise, the ISO8601 format is used. The resulting string is
2118 .. method:: formatException(exc_info)
2120 Formats the specified exception information (a standard exception tuple as
2121 returned by :func:`sys.exc_info`) as a string. This default implementation
2122 just uses :func:`traceback.print_exception`. The resulting string is
2129 :class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
2130 more sophisticated filtering than is provided by levels. The base filter class
2131 only allows events which are below a certain point in the logger hierarchy. For
2132 example, a filter initialized with "A.B" will allow events logged by loggers
2133 "A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
2134 initialized with the empty string, all events are passed.
2137 .. class:: Filter([name])
2139 Returns an instance of the :class:`Filter` class. If *name* is specified, it
2140 names a logger which, together with its children, will have its events allowed
2141 through the filter. If no name is specified, allows every event.
2144 .. method:: filter(record)
2146 Is the specified record to be logged? Returns zero for no, nonzero for
2147 yes. If deemed appropriate, the record may be modified in-place by this
2154 :class:`LogRecord` instances are created every time something is logged. They
2155 contain all the information pertinent to the event being logged. The main
2156 information passed in is in msg and args, which are combined using msg % args to
2157 create the message field of the record. The record also includes information
2158 such as when the record was created, the source line where the logging call was
2159 made, and any exception information to be logged.
2162 .. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2164 Returns an instance of :class:`LogRecord` initialized with interesting
2165 information. The *name* is the logger name; *lvl* is the numeric level;
2166 *pathname* is the absolute pathname of the source file in which the logging
2167 call was made; *lineno* is the line number in that file where the logging
2168 call is found; *msg* is the user-supplied message (a format string); *args*
2169 is the tuple which, together with *msg*, makes up the user message; and
2170 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2171 (or :const:`None`, if no exception information is available). The *func* is
2172 the name of the function from which the logging call was made. If not
2173 specified, it defaults to ``None``.
2175 .. versionchanged:: 2.5
2179 .. method:: getMessage()
2181 Returns the message for this :class:`LogRecord` instance after merging any
2182 user-supplied arguments with the message.
2185 LoggerAdapter Objects
2186 ---------------------
2188 .. versionadded:: 2.6
2190 :class:`LoggerAdapter` instances are used to conveniently pass contextual
2191 information into logging calls. For a usage example , see the section on
2192 `adding contextual information to your logging output`__.
2196 .. class:: LoggerAdapter(logger, extra)
2198 Returns an instance of :class:`LoggerAdapter` initialized with an
2199 underlying :class:`Logger` instance and a dict-like object.
2201 .. method:: process(msg, kwargs)
2203 Modifies the message and/or keyword arguments passed to a logging call in
2204 order to insert contextual information. This implementation takes the object
2205 passed as *extra* to the constructor and adds it to *kwargs* using key
2206 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
2207 (possibly modified) versions of the arguments passed in.
2209 In addition to the above, :class:`LoggerAdapter` supports all the logging
2210 methods of :class:`Logger`, i.e. :meth:`debug`, :meth:`info`, :meth:`warning`,
2211 :meth:`error`, :meth:`exception`, :meth:`critical` and :meth:`log`. These
2212 methods have the same signatures as their counterparts in :class:`Logger`, so
2213 you can use the two types of instances interchangeably.
2219 The logging module is intended to be thread-safe without any special work
2220 needing to be done by its clients. It achieves this though using threading
2221 locks; there is one lock to serialize access to the module's shared data, and
2222 each handler also creates a lock to serialize access to its underlying I/O.
2229 .. _logging-config-api:
2231 Configuration functions
2232 ^^^^^^^^^^^^^^^^^^^^^^^
2234 The following functions configure the logging module. They are located in the
2235 :mod:`logging.config` module. Their use is optional --- you can configure the
2236 logging module using these functions or by making calls to the main API (defined
2237 in :mod:`logging` itself) and defining handlers which are declared either in
2238 :mod:`logging` or :mod:`logging.handlers`.
2241 .. function:: fileConfig(fname[, defaults])
2243 Reads the logging configuration from a :mod:`configparser`\-format file named
2244 *fname*. This function can be called several times from an application,
2245 allowing an end user the ability to select from various pre-canned
2246 configurations (if the developer provides a mechanism to present the choices
2247 and load the chosen configuration). Defaults to be passed to the ConfigParser
2248 can be specified in the *defaults* argument.
2251 .. function:: listen([port])
2253 Starts up a socket server on the specified port, and listens for new
2254 configurations. If no port is specified, the module's default
2255 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2256 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2257 :class:`Thread` instance on which you can call :meth:`start` to start the
2258 server, and which you can :meth:`join` when appropriate. To stop the server,
2259 call :func:`stopListening`.
2261 To send a configuration to the socket, read in the configuration file and
2262 send it to the socket as a string of bytes preceded by a four-byte length
2263 string packed in binary using ``struct.pack('>L', n)``.
2266 .. function:: stopListening()
2268 Stops the listening server which was created with a call to :func:`listen`.
2269 This is typically called before calling :meth:`join` on the return value from
2273 .. _logging-config-fileformat:
2275 Configuration file format
2276 ^^^^^^^^^^^^^^^^^^^^^^^^^
2278 The configuration file format understood by :func:`fileConfig` is
2279 based on :mod:`configparser` functionality. The file must contain
2280 sections called ``[loggers]``, ``[handlers]`` and ``[formatters]``
2281 which identify by name the entities of each type which are defined in
2282 the file. For each such entity, there is a separate section which
2283 identified how that entity is configured. Thus, for a logger named
2284 ``log01`` in the ``[loggers]`` section, the relevant configuration
2285 details are held in a section ``[logger_log01]``. Similarly, a handler
2286 called ``hand01`` in the ``[handlers]`` section will have its
2287 configuration held in a section called ``[handler_hand01]``, while a
2288 formatter called ``form01`` in the ``[formatters]`` section will have
2289 its configuration specified in a section called
2290 ``[formatter_form01]``. The root logger configuration must be
2291 specified in a section called ``[logger_root]``.
2293 Examples of these sections in the file are given below. ::
2296 keys=root,log02,log03,log04,log05,log06,log07
2299 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2302 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2304 The root logger must specify a level and a list of handlers. An example of a
2305 root logger section is given below. ::
2311 The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2312 ``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2313 logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2314 package's namespace.
2316 The ``handlers`` entry is a comma-separated list of handler names, which must
2317 appear in the ``[handlers]`` section. These names must appear in the
2318 ``[handlers]`` section and have corresponding sections in the configuration
2321 For loggers other than the root logger, some additional information is required.
2322 This is illustrated by the following example. ::
2328 qualname=compiler.parser
2330 The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2331 except that if a non-root logger's level is specified as ``NOTSET``, the system
2332 consults loggers higher up the hierarchy to determine the effective level of the
2333 logger. The ``propagate`` entry is set to 1 to indicate that messages must
2334 propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2335 indicate that messages are **not** propagated to handlers up the hierarchy. The
2336 ``qualname`` entry is the hierarchical channel name of the logger, that is to
2337 say the name used by the application to get the logger.
2339 Sections which specify handler configuration are exemplified by the following.
2348 The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2349 in the ``logging`` package's namespace). The ``level`` is interpreted as for
2350 loggers, and ``NOTSET`` is taken to mean "log everything".
2352 The ``formatter`` entry indicates the key name of the formatter for this
2353 handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2354 If a name is specified, it must appear in the ``[formatters]`` section and have
2355 a corresponding section in the configuration file.
2357 The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2358 package's namespace, is the list of arguments to the constructor for the handler
2359 class. Refer to the constructors for the relevant handlers, or to the examples
2360 below, to see how typical entries are constructed. ::
2366 args=('python.log', 'w')
2369 class=handlers.SocketHandler
2372 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2375 class=handlers.DatagramHandler
2378 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2381 class=handlers.SysLogHandler
2384 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2387 class=handlers.NTEventLogHandler
2390 args=('Python Application', '', 'Application')
2393 class=handlers.SMTPHandler
2396 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2399 class=handlers.MemoryHandler
2406 class=handlers.HTTPHandler
2409 args=('localhost:9022', '/log', 'GET')
2411 Sections which specify formatter configuration are typified by the following. ::
2414 format=F1 %(asctime)s %(levelname)s %(message)s
2416 class=logging.Formatter
2418 The ``format`` entry is the overall format string, and the ``datefmt`` entry is
2419 the :func:`strftime`\ -compatible date/time format string. If empty, the
2420 package substitutes ISO8601 format date/times, which is almost equivalent to
2421 specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2422 also specifies milliseconds, which are appended to the result of using the above
2423 format string, with a comma separator. An example time in ISO8601 format is
2424 ``2003-01-23 00:29:50,411``.
2426 The ``class`` entry is optional. It indicates the name of the formatter's class
2427 (as a dotted module and class name.) This option is useful for instantiating a
2428 :class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2429 exception tracebacks in an expanded or condensed format.
2432 Configuration server example
2433 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2435 Here is an example of a module using the logging configuration server::
2438 import logging.config
2442 # read initial config file
2443 logging.config.fileConfig("logging.conf")
2445 # create and start listener on port 9999
2446 t = logging.config.listen(9999)
2449 logger = logging.getLogger("simpleExample")
2452 # loop through logging calls to see the difference
2453 # new configurations make, until Ctrl+C is pressed
2455 logger.debug("debug message")
2456 logger.info("info message")
2457 logger.warn("warn message")
2458 logger.error("error message")
2459 logger.critical("critical message")
2461 except KeyboardInterrupt:
2463 logging.config.stopListening()
2466 And here is a script that takes a filename and sends that file to the server,
2467 properly preceded with the binary-encoded length, as the new logging
2470 #!/usr/bin/env python
2471 import socket, sys, struct
2473 data_to_send = open(sys.argv[1], "r").read()
2477 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2478 print "connecting..."
2479 s.connect((HOST, PORT))
2480 print "sending config..."
2481 s.send(struct.pack(">L", len(data_to_send)))
2482 s.send(data_to_send)
2490 Multiple handlers and formatters
2491 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2493 Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2494 or maximum quota for the number of handlers you may add. Sometimes it will be
2495 beneficial for an application to log all messages of all severities to a text
2496 file while simultaneously logging errors or above to the console. To set this
2497 up, simply configure the appropriate handlers. The logging calls in the
2498 application code will remain unchanged. Here is a slight modification to the
2499 previous simple module-based configuration example::
2503 logger = logging.getLogger("simple_example")
2504 logger.setLevel(logging.DEBUG)
2505 # create file handler which logs even debug messages
2506 fh = logging.FileHandler("spam.log")
2507 fh.setLevel(logging.DEBUG)
2508 # create console handler with a higher log level
2509 ch = logging.StreamHandler()
2510 ch.setLevel(logging.ERROR)
2511 # create formatter and add it to the handlers
2512 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2513 ch.setFormatter(formatter)
2514 fh.setFormatter(formatter)
2515 # add the handlers to logger
2516 logger.addHandler(ch)
2517 logger.addHandler(fh)
2519 # "application" code
2520 logger.debug("debug message")
2521 logger.info("info message")
2522 logger.warn("warn message")
2523 logger.error("error message")
2524 logger.critical("critical message")
2526 Notice that the "application" code does not care about multiple handlers. All
2527 that changed was the addition and configuration of a new handler named *fh*.
2529 The ability to create new handlers with higher- or lower-severity filters can be
2530 very helpful when writing and testing an application. Instead of using many
2531 ``print`` statements for debugging, use ``logger.debug``: Unlike the print
2532 statements, which you will have to delete or comment out later, the logger.debug
2533 statements can remain intact in the source code and remain dormant until you
2534 need them again. At that time, the only change that needs to happen is to
2535 modify the severity level of the logger and/or handler to debug.
2538 Using logging in multiple modules
2539 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2541 It was mentioned above that multiple calls to
2542 ``logging.getLogger('someLogger')`` return a reference to the same logger
2543 object. This is true not only within the same module, but also across modules
2544 as long as it is in the same Python interpreter process. It is true for
2545 references to the same object; additionally, application code can define and
2546 configure a parent logger in one module and create (but not configure) a child
2547 logger in a separate module, and all logger calls to the child will pass up to
2548 the parent. Here is a main module::
2551 import auxiliary_module
2553 # create logger with "spam_application"
2554 logger = logging.getLogger("spam_application")
2555 logger.setLevel(logging.DEBUG)
2556 # create file handler which logs even debug messages
2557 fh = logging.FileHandler("spam.log")
2558 fh.setLevel(logging.DEBUG)
2559 # create console handler with a higher log level
2560 ch = logging.StreamHandler()
2561 ch.setLevel(logging.ERROR)
2562 # create formatter and add it to the handlers
2563 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2564 fh.setFormatter(formatter)
2565 ch.setFormatter(formatter)
2566 # add the handlers to the logger
2567 logger.addHandler(fh)
2568 logger.addHandler(ch)
2570 logger.info("creating an instance of auxiliary_module.Auxiliary")
2571 a = auxiliary_module.Auxiliary()
2572 logger.info("created an instance of auxiliary_module.Auxiliary")
2573 logger.info("calling auxiliary_module.Auxiliary.do_something")
2575 logger.info("finished auxiliary_module.Auxiliary.do_something")
2576 logger.info("calling auxiliary_module.some_function()")
2577 auxiliary_module.some_function()
2578 logger.info("done with auxiliary_module.some_function()")
2580 Here is the auxiliary module::
2585 module_logger = logging.getLogger("spam_application.auxiliary")
2589 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2590 self.logger.info("creating an instance of Auxiliary")
2591 def do_something(self):
2592 self.logger.info("doing something")
2594 self.logger.info("done doing something")
2596 def some_function():
2597 module_logger.info("received a call to \"some_function\"")
2599 The output looks like this::
2601 2005-03-23 23:47:11,663 - spam_application - INFO -
2602 creating an instance of auxiliary_module.Auxiliary
2603 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
2604 creating an instance of Auxiliary
2605 2005-03-23 23:47:11,665 - spam_application - INFO -
2606 created an instance of auxiliary_module.Auxiliary
2607 2005-03-23 23:47:11,668 - spam_application - INFO -
2608 calling auxiliary_module.Auxiliary.do_something
2609 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
2611 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
2612 done doing something
2613 2005-03-23 23:47:11,670 - spam_application - INFO -
2614 finished auxiliary_module.Auxiliary.do_something
2615 2005-03-23 23:47:11,671 - spam_application - INFO -
2616 calling auxiliary_module.some_function()
2617 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
2618 received a call to "some_function"
2619 2005-03-23 23:47:11,673 - spam_application - INFO -
2620 done with auxiliary_module.some_function()