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 mechnisms 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 a name of name
249 if a name 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 hander 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 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 .. versionchanged:: 2.4
702 Formerly, :func:`basicConfig` did not take any keyword arguments.
704 The following keyword arguments are supported.
706 +--------------+---------------------------------------------+
707 | Format | Description |
708 +==============+=============================================+
709 | ``filename`` | Specifies that a FileHandler be created, |
710 | | using the specified filename, rather than a |
712 +--------------+---------------------------------------------+
713 | ``filemode`` | Specifies the mode to open the file, if |
714 | | filename is specified (if filemode is |
715 | | unspecified, it defaults to 'a'). |
716 +--------------+---------------------------------------------+
717 | ``format`` | Use the specified format string for the |
719 +--------------+---------------------------------------------+
720 | ``datefmt`` | Use the specified date/time format. |
721 +--------------+---------------------------------------------+
722 | ``level`` | Set the root logger level to the specified |
724 +--------------+---------------------------------------------+
725 | ``stream`` | Use the specified stream to initialize the |
726 | | StreamHandler. Note that this argument is |
727 | | incompatible with 'filename' - if both are |
728 | | present, 'stream' is ignored. |
729 +--------------+---------------------------------------------+
732 .. function:: shutdown()
734 Informs the logging system to perform an orderly shutdown by flushing and
735 closing all handlers.
738 .. function:: setLoggerClass(klass)
740 Tells the logging system to use the class *klass* when instantiating a logger.
741 The class should define :meth:`__init__` such that only a name argument is
742 required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
743 function is typically called before any loggers are instantiated by applications
744 which need to use custom logger behavior.
749 :pep:`282` - A Logging System
750 The proposal which described this feature for inclusion in the Python standard
753 `Original Python logging package <http://www.red-dove.com/python_logging.html>`_
754 This is the original source for the :mod:`logging` package. The version of the
755 package available from this site is suitable for use with Python 1.5.2, 2.1.x
756 and 2.2.x, which do not include the :mod:`logging` package in the standard
763 Loggers have the following attributes and methods. Note that Loggers are never
764 instantiated directly, but always through the module-level function
765 ``logging.getLogger(name)``.
768 .. attribute:: Logger.propagate
770 If this evaluates to false, logging messages are not passed by this logger or by
771 child loggers to higher level (ancestor) loggers. The constructor sets this
775 .. method:: Logger.setLevel(lvl)
777 Sets the threshold for this logger to *lvl*. Logging messages which are less
778 severe than *lvl* will be ignored. When a logger is created, the level is set to
779 :const:`NOTSET` (which causes all messages to be processed when the logger is
780 the root logger, or delegation to the parent when the logger is a non-root
781 logger). Note that the root logger is created with level :const:`WARNING`.
783 The term "delegation to the parent" means that if a logger has a level of
784 NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
785 a level other than NOTSET is found, or the root is reached.
787 If an ancestor is found with a level other than NOTSET, then that ancestor's
788 level is treated as the effective level of the logger where the ancestor search
789 began, and is used to determine how a logging event is handled.
791 If the root is reached, and it has a level of NOTSET, then all messages will be
792 processed. Otherwise, the root's level will be used as the effective level.
795 .. method:: Logger.isEnabledFor(lvl)
797 Indicates if a message of severity *lvl* would be processed by this logger.
798 This method checks first the module-level level set by
799 ``logging.disable(lvl)`` and then the logger's effective level as determined
800 by :meth:`getEffectiveLevel`.
803 .. method:: Logger.getEffectiveLevel()
805 Indicates the effective level for this logger. If a value other than
806 :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
807 the hierarchy is traversed towards the root until a value other than
808 :const:`NOTSET` is found, and that value is returned.
811 .. method:: Logger.debug(msg[, *args[, **kwargs]])
813 Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
814 message format string, and the *args* are the arguments which are merged into
815 *msg* using the string formatting operator. (Note that this means that you can
816 use keywords in the format string, together with a single dictionary argument.)
818 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
819 which, if it does not evaluate as false, causes exception information to be
820 added to the logging message. If an exception tuple (in the format returned by
821 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
822 is called to get the exception information.
824 The other optional keyword argument is *extra* which can be used to pass a
825 dictionary which is used to populate the __dict__ of the LogRecord created for
826 the logging event with user-defined attributes. These custom attributes can then
827 be used as you like. For example, they could be incorporated into logged
828 messages. For example::
830 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
831 logging.basicConfig(format=FORMAT)
832 d = { 'clientip' : '192.168.0.1', 'user' : 'fbloggs' }
833 logger = logging.getLogger("tcpserver")
834 logger.warning("Protocol problem: %s", "connection reset", extra=d)
836 would print something like ::
838 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
840 The keys in the dictionary passed in *extra* should not clash with the keys used
841 by the logging system. (See the :class:`Formatter` documentation for more
842 information on which keys are used by the logging system.)
844 If you choose to use these attributes in logged messages, you need to exercise
845 some care. In the above example, for instance, the :class:`Formatter` has been
846 set up with a format string which expects 'clientip' and 'user' in the attribute
847 dictionary of the LogRecord. If these are missing, the message will not be
848 logged because a string formatting exception will occur. So in this case, you
849 always need to pass the *extra* dictionary with these keys.
851 While this might be annoying, this feature is intended for use in specialized
852 circumstances, such as multi-threaded servers where the same code executes in
853 many contexts, and interesting conditions which arise are dependent on this
854 context (such as remote client IP address and authenticated user name, in the
855 above example). In such circumstances, it is likely that specialized
856 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
858 .. versionchanged:: 2.5
862 .. method:: Logger.info(msg[, *args[, **kwargs]])
864 Logs a message with level :const:`INFO` on this logger. The arguments are
865 interpreted as for :meth:`debug`.
868 .. method:: Logger.warning(msg[, *args[, **kwargs]])
870 Logs a message with level :const:`WARNING` on this logger. The arguments are
871 interpreted as for :meth:`debug`.
874 .. method:: Logger.error(msg[, *args[, **kwargs]])
876 Logs a message with level :const:`ERROR` on this logger. The arguments are
877 interpreted as for :meth:`debug`.
880 .. method:: Logger.critical(msg[, *args[, **kwargs]])
882 Logs a message with level :const:`CRITICAL` on this logger. The arguments are
883 interpreted as for :meth:`debug`.
886 .. method:: Logger.log(lvl, msg[, *args[, **kwargs]])
888 Logs a message with integer level *lvl* on this logger. The other arguments are
889 interpreted as for :meth:`debug`.
892 .. method:: Logger.exception(msg[, *args])
894 Logs a message with level :const:`ERROR` on this logger. The arguments are
895 interpreted as for :meth:`debug`. Exception info is added to the logging
896 message. This method should only be called from an exception handler.
899 .. method:: Logger.addFilter(filt)
901 Adds the specified filter *filt* to this logger.
904 .. method:: Logger.removeFilter(filt)
906 Removes the specified filter *filt* from this logger.
909 .. method:: Logger.filter(record)
911 Applies this logger's filters to the record and returns a true value if the
912 record is to be processed.
915 .. method:: Logger.addHandler(hdlr)
917 Adds the specified handler *hdlr* to this logger.
920 .. method:: Logger.removeHandler(hdlr)
922 Removes the specified handler *hdlr* from this logger.
925 .. method:: Logger.findCaller()
927 Finds the caller's source filename and line number. Returns the filename, line
928 number and function name as a 3-element tuple.
930 .. versionchanged:: 2.4
931 The function name was added. In earlier versions, the filename and line number
932 were returned as a 2-element tuple..
935 .. method:: Logger.handle(record)
937 Handles a record by passing it to all handlers associated with this logger and
938 its ancestors (until a false value of *propagate* is found). This method is used
939 for unpickled records received from a socket, as well as those created locally.
940 Logger-level filtering is applied using :meth:`filter`.
943 .. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info [, func, extra])
945 This is a factory method which can be overridden in subclasses to create
946 specialized :class:`LogRecord` instances.
948 .. versionchanged:: 2.5
949 *func* and *extra* were added.
957 .. versionchanged:: 2.4
958 formerly :func:`basicConfig` did not take any keyword arguments.
960 The :mod:`logging` package provides a lot of flexibility, and its configuration
961 can appear daunting. This section demonstrates that simple use of the logging
964 The simplest example shows logging to the console::
968 logging.debug('A debug message')
969 logging.info('Some information')
970 logging.warning('A shot across the bows')
972 If you run the above script, you'll see this::
974 WARNING:root:A shot across the bows
976 Because no particular logger was specified, the system used the root logger. The
977 debug and info messages didn't appear because by default, the root logger is
978 configured to only handle messages with a severity of WARNING or above. The
979 message format is also a configuration default, as is the output destination of
980 the messages - ``sys.stderr``. The severity level, the message format and
981 destination can be easily changed, as shown in the example below::
985 logging.basicConfig(level=logging.DEBUG,
986 format='%(asctime)s %(levelname)s %(message)s',
987 filename='/tmp/myapp.log',
989 logging.debug('A debug message')
990 logging.info('Some information')
991 logging.warning('A shot across the bows')
993 The :meth:`basicConfig` method is used to change the configuration defaults,
994 which results in output (written to ``/tmp/myapp.log``) which should look
995 something like the following::
997 2004-07-02 13:00:08,743 DEBUG A debug message
998 2004-07-02 13:00:08,743 INFO Some information
999 2004-07-02 13:00:08,743 WARNING A shot across the bows
1001 This time, all messages with a severity of DEBUG or above were handled, and the
1002 format of the messages was also changed, and output went to the specified file
1003 rather than the console.
1005 Formatting uses standard Python string formatting - see section
1006 :ref:`string-formatting`. The format string takes the following common
1007 specifiers. For a complete list of specifiers, consult the :class:`Formatter`
1010 +-------------------+-----------------------------------------------+
1011 | Format | Description |
1012 +===================+===============================================+
1013 | ``%(name)s`` | Name of the logger (logging channel). |
1014 +-------------------+-----------------------------------------------+
1015 | ``%(levelname)s`` | Text logging level for the message |
1016 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1017 | | ``'ERROR'``, ``'CRITICAL'``). |
1018 +-------------------+-----------------------------------------------+
1019 | ``%(asctime)s`` | Human-readable time when the |
1020 | | :class:`LogRecord` was created. By default |
1021 | | this is of the form "2003-07-08 16:49:45,896" |
1022 | | (the numbers after the comma are millisecond |
1023 | | portion of the time). |
1024 +-------------------+-----------------------------------------------+
1025 | ``%(message)s`` | The logged message. |
1026 +-------------------+-----------------------------------------------+
1028 To change the date/time format, you can pass an additional keyword parameter,
1029 *datefmt*, as in the following::
1033 logging.basicConfig(level=logging.DEBUG,
1034 format='%(asctime)s %(levelname)-8s %(message)s',
1035 datefmt='%a, %d %b %Y %H:%M:%S',
1036 filename='/temp/myapp.log',
1038 logging.debug('A debug message')
1039 logging.info('Some information')
1040 logging.warning('A shot across the bows')
1042 which would result in output like ::
1044 Fri, 02 Jul 2004 13:06:18 DEBUG A debug message
1045 Fri, 02 Jul 2004 13:06:18 INFO Some information
1046 Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows
1048 The date format string follows the requirements of :func:`strftime` - see the
1049 documentation for the :mod:`time` module.
1051 If, instead of sending logging output to the console or a file, you'd rather use
1052 a file-like object which you have created separately, you can pass it to
1053 :func:`basicConfig` using the *stream* keyword argument. Note that if both
1054 *stream* and *filename* keyword arguments are passed, the *stream* argument is
1057 Of course, you can put variable information in your output. To do this, simply
1058 have the message be a format string and pass in additional arguments containing
1059 the variable information, as in the following example::
1063 logging.basicConfig(level=logging.DEBUG,
1064 format='%(asctime)s %(levelname)-8s %(message)s',
1065 datefmt='%a, %d %b %Y %H:%M:%S',
1066 filename='/temp/myapp.log',
1068 logging.error('Pack my box with %d dozen %s', 5, 'liquor jugs')
1070 which would result in ::
1072 Wed, 21 Jul 2004 15:35:16 ERROR Pack my box with 5 dozen liquor jugs
1075 .. _multiple-destinations:
1077 Logging to multiple destinations
1078 --------------------------------
1080 Let's say you want to log to console and file with different message formats and
1081 in differing circumstances. Say you want to log messages with levels of DEBUG
1082 and higher to file, and those messages at level INFO and higher to the console.
1083 Let's also assume that the file should contain timestamps, but the console
1084 messages should not. Here's how you can achieve this::
1088 # set up logging to file - see previous section for more details
1089 logging.basicConfig(level=logging.DEBUG,
1090 format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
1091 datefmt='%m-%d %H:%M',
1092 filename='/temp/myapp.log',
1094 # define a Handler which writes INFO messages or higher to the sys.stderr
1095 console = logging.StreamHandler()
1096 console.setLevel(logging.INFO)
1097 # set a format which is simpler for console use
1098 formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
1099 # tell the handler to use this format
1100 console.setFormatter(formatter)
1101 # add the handler to the root logger
1102 logging.getLogger('').addHandler(console)
1104 # Now, we can log to the root logger, or any other logger. First the root...
1105 logging.info('Jackdaws love my big sphinx of quartz.')
1107 # Now, define a couple of other loggers which might represent areas in your
1110 logger1 = logging.getLogger('myapp.area1')
1111 logger2 = logging.getLogger('myapp.area2')
1113 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1114 logger1.info('How quickly daft jumping zebras vex.')
1115 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1116 logger2.error('The five boxing wizards jump quickly.')
1118 When you run this, on the console you will see ::
1120 root : INFO Jackdaws love my big sphinx of quartz.
1121 myapp.area1 : INFO How quickly daft jumping zebras vex.
1122 myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
1123 myapp.area2 : ERROR The five boxing wizards jump quickly.
1125 and in the file you will see something like ::
1127 10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
1128 10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1129 10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
1130 10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1131 10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
1133 As you can see, the DEBUG message only shows up in the file. The other messages
1134 are sent to both destinations.
1136 This example uses console and file handlers, but you can use any number and
1137 combination of handlers you choose.
1140 .. _network-logging:
1142 Sending and receiving logging events across a network
1143 -----------------------------------------------------
1145 Let's say you want to send logging events across a network, and handle them at
1146 the receiving end. A simple way of doing this is attaching a
1147 :class:`SocketHandler` instance to the root logger at the sending end::
1149 import logging, logging.handlers
1151 rootLogger = logging.getLogger('')
1152 rootLogger.setLevel(logging.DEBUG)
1153 socketHandler = logging.handlers.SocketHandler('localhost',
1154 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1155 # don't bother with a formatter, since a socket handler sends the event as
1156 # an unformatted pickle
1157 rootLogger.addHandler(socketHandler)
1159 # Now, we can log to the root logger, or any other logger. First the root...
1160 logging.info('Jackdaws love my big sphinx of quartz.')
1162 # Now, define a couple of other loggers which might represent areas in your
1165 logger1 = logging.getLogger('myapp.area1')
1166 logger2 = logging.getLogger('myapp.area2')
1168 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1169 logger1.info('How quickly daft jumping zebras vex.')
1170 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1171 logger2.error('The five boxing wizards jump quickly.')
1173 At the receiving end, you can set up a receiver using the :mod:`SocketServer`
1174 module. Here is a basic working example::
1178 import logging.handlers
1183 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
1184 """Handler for a streaming logging request.
1186 This basically logs the record using whatever logging policy is
1192 Handle multiple requests - each expected to be a 4-byte length,
1193 followed by the LogRecord in pickle format. Logs the record
1194 according to whatever policy is configured locally.
1197 chunk = self.connection.recv(4)
1200 slen = struct.unpack(">L", chunk)[0]
1201 chunk = self.connection.recv(slen)
1202 while len(chunk) < slen:
1203 chunk = chunk + self.connection.recv(slen - len(chunk))
1204 obj = self.unPickle(chunk)
1205 record = logging.makeLogRecord(obj)
1206 self.handleLogRecord(record)
1208 def unPickle(self, data):
1209 return cPickle.loads(data)
1211 def handleLogRecord(self, record):
1212 # if a name is specified, we use the named logger rather than the one
1213 # implied by the record.
1214 if self.server.logname is not None:
1215 name = self.server.logname
1218 logger = logging.getLogger(name)
1219 # N.B. EVERY record gets logged. This is because Logger.handle
1220 # is normally called AFTER logger-level filtering. If you want
1221 # to do filtering, do it at the client end to save wasting
1222 # cycles and network bandwidth!
1223 logger.handle(record)
1225 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
1226 """simple TCP socket-based logging receiver suitable for testing.
1229 allow_reuse_address = 1
1231 def __init__(self, host='localhost',
1232 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1233 handler=LogRecordStreamHandler):
1234 SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
1239 def serve_until_stopped(self):
1243 rd, wr, ex = select.select([self.socket.fileno()],
1247 self.handle_request()
1251 logging.basicConfig(
1252 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1253 tcpserver = LogRecordSocketReceiver()
1254 print "About to start TCP server..."
1255 tcpserver.serve_until_stopped()
1257 if __name__ == "__main__":
1260 First run the server, and then the client. On the client side, nothing is
1261 printed on the console; on the server side, you should see something like::
1263 About to start TCP server...
1264 59 root INFO Jackdaws love my big sphinx of quartz.
1265 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1266 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1267 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1268 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1274 Handlers have the following attributes and methods. Note that :class:`Handler`
1275 is never instantiated directly; this class acts as a base for more useful
1276 subclasses. However, the :meth:`__init__` method in subclasses needs to call
1277 :meth:`Handler.__init__`.
1280 .. method:: Handler.__init__(level=NOTSET)
1282 Initializes the :class:`Handler` instance by setting its level, setting the list
1283 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1284 serializing access to an I/O mechanism.
1287 .. method:: Handler.createLock()
1289 Initializes a thread lock which can be used to serialize access to underlying
1290 I/O functionality which may not be threadsafe.
1293 .. method:: Handler.acquire()
1295 Acquires the thread lock created with :meth:`createLock`.
1298 .. method:: Handler.release()
1300 Releases the thread lock acquired with :meth:`acquire`.
1303 .. method:: Handler.setLevel(lvl)
1305 Sets the threshold for this handler to *lvl*. Logging messages which are less
1306 severe than *lvl* will be ignored. When a handler is created, the level is set
1307 to :const:`NOTSET` (which causes all messages to be processed).
1310 .. method:: Handler.setFormatter(form)
1312 Sets the :class:`Formatter` for this handler to *form*.
1315 .. method:: Handler.addFilter(filt)
1317 Adds the specified filter *filt* to this handler.
1320 .. method:: Handler.removeFilter(filt)
1322 Removes the specified filter *filt* from this handler.
1325 .. method:: Handler.filter(record)
1327 Applies this handler's filters to the record and returns a true value if the
1328 record is to be processed.
1331 .. method:: Handler.flush()
1333 Ensure all logging output has been flushed. This version does nothing and is
1334 intended to be implemented by subclasses.
1337 .. method:: Handler.close()
1339 Tidy up any resources used by the handler. This version does nothing and is
1340 intended to be implemented by subclasses.
1343 .. method:: Handler.handle(record)
1345 Conditionally emits the specified logging record, depending on filters which may
1346 have been added to the handler. Wraps the actual emission of the record with
1347 acquisition/release of the I/O thread lock.
1350 .. method:: Handler.handleError(record)
1352 This method should be called from handlers when an exception is encountered
1353 during an :meth:`emit` call. By default it does nothing, which means that
1354 exceptions get silently ignored. This is what is mostly wanted for a logging
1355 system - most users will not care about errors in the logging system, they are
1356 more interested in application errors. You could, however, replace this with a
1357 custom handler if you wish. The specified record is the one which was being
1358 processed when the exception occurred.
1361 .. method:: Handler.format(record)
1363 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1364 default formatter for the module.
1367 .. method:: Handler.emit(record)
1369 Do whatever it takes to actually log the specified logging record. This version
1370 is intended to be implemented by subclasses and so raises a
1371 :exc:`NotImplementedError`.
1377 The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1378 sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1379 file-like object (or, more precisely, any object which supports :meth:`write`
1380 and :meth:`flush` methods).
1383 .. class:: StreamHandler([strm])
1385 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1386 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1390 .. method:: StreamHandler.emit(record)
1392 If a formatter is specified, it is used to format the record. The record is then
1393 written to the stream with a trailing newline. If exception information is
1394 present, it is formatted using :func:`traceback.print_exception` and appended to
1398 .. method:: StreamHandler.flush()
1400 Flushes the stream by calling its :meth:`flush` method. Note that the
1401 :meth:`close` method is inherited from :class:`Handler` and so does nothing, so
1402 an explicit :meth:`flush` call may be needed at times.
1408 The :class:`FileHandler` class, located in the core :mod:`logging` package,
1409 sends logging output to a disk file. It inherits the output functionality from
1410 :class:`StreamHandler`.
1413 .. class:: FileHandler(filename[, mode[, encoding]])
1415 Returns a new instance of the :class:`FileHandler` class. The specified file is
1416 opened and used as the stream for logging. If *mode* is not specified,
1417 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1418 with that encoding. By default, the file grows indefinitely.
1421 .. method:: FileHandler.close()
1426 .. method:: FileHandler.emit(record)
1428 Outputs the record to the file.
1434 .. versionadded:: 2.6
1436 The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1437 module, is a :class:`FileHandler` which watches the file it is logging to. If
1438 the file changes, it is closed and reopened using the file name.
1440 A file change can happen because of usage of programs such as *newsyslog* and
1441 *logrotate* which perform log file rotation. This handler, intended for use
1442 under Unix/Linux, watches the file to see if it has changed since the last emit.
1443 (A file is deemed to have changed if its device or inode have changed.) If the
1444 file has changed, the old file stream is closed, and the file opened to get a
1447 This handler is not appropriate for use under Windows, because under Windows
1448 open log files cannot be moved or renamed - logging opens the files with
1449 exclusive locks - and so there is no need for such a handler. Furthermore,
1450 *ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1454 .. class:: WatchedFileHandler(filename[,mode[, encoding]])
1456 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1457 file is opened and used as the stream for logging. If *mode* is not specified,
1458 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1459 with that encoding. By default, the file grows indefinitely.
1462 .. method:: WatchedFileHandler.emit(record)
1464 Outputs the record to the file, but first checks to see if the file has changed.
1465 If it has, the existing stream is flushed and closed and the file opened again,
1466 before outputting the record to the file.
1472 The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1473 module, supports rotation of disk log files.
1476 .. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount]]])
1478 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1479 file is opened and used as the stream for logging. If *mode* is not specified,
1480 ``'a'`` is used. By default, the file grows indefinitely.
1482 You can use the *maxBytes* and *backupCount* values to allow the file to
1483 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1484 the file is closed and a new file is silently opened for output. Rollover occurs
1485 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1486 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1487 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1488 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1489 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1490 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1491 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1492 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1493 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1496 .. method:: RotatingFileHandler.doRollover()
1498 Does a rollover, as described above.
1501 .. method:: RotatingFileHandler.emit(record)
1503 Outputs the record to the file, catering for rollover as described previously.
1506 TimedRotatingFileHandler
1507 ^^^^^^^^^^^^^^^^^^^^^^^^
1509 The :class:`TimedRotatingFileHandler` class, located in the
1510 :mod:`logging.handlers` module, supports rotation of disk log files at certain
1514 .. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount]]])
1516 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1517 specified file is opened and used as the stream for logging. On rotating it also
1518 sets the filename suffix. Rotating happens based on the product of *when* and
1521 You can use the *when* to specify the type of *interval*. The list of possible
1522 values is, note that they are not case sensitive:
1524 +----------+-----------------------+
1525 | Value | Type of interval |
1526 +==========+=======================+
1528 +----------+-----------------------+
1530 +----------+-----------------------+
1532 +----------+-----------------------+
1534 +----------+-----------------------+
1535 | W | Week day (0=Monday) |
1536 +----------+-----------------------+
1537 | midnight | Roll over at midnight |
1538 +----------+-----------------------+
1540 If *backupCount* is non-zero, the system will save old log files by appending
1541 extensions to the filename. The extensions are date-and-time based, using the
1542 strftime format ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on
1543 the rollover interval. At most *backupCount* files will be kept, and if more
1544 would be created when rollover occurs, the oldest one is deleted.
1547 .. method:: TimedRotatingFileHandler.doRollover()
1549 Does a rollover, as described above.
1552 .. method:: TimedRotatingFileHandler.emit(record)
1554 Outputs the record to the file, catering for rollover as described above.
1560 The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1561 sends logging output to a network socket. The base class uses a TCP socket.
1564 .. class:: SocketHandler(host, port)
1566 Returns a new instance of the :class:`SocketHandler` class intended to
1567 communicate with a remote machine whose address is given by *host* and *port*.
1570 .. method:: SocketHandler.close()
1575 .. method:: SocketHandler.emit()
1577 Pickles the record's attribute dictionary and writes it to the socket in binary
1578 format. If there is an error with the socket, silently drops the packet. If the
1579 connection was previously lost, re-establishes the connection. To unpickle the
1580 record at the receiving end into a :class:`LogRecord`, use the
1581 :func:`makeLogRecord` function.
1584 .. method:: SocketHandler.handleError()
1586 Handles an error which has occurred during :meth:`emit`. The most likely cause
1587 is a lost connection. Closes the socket so that we can retry on the next event.
1590 .. method:: SocketHandler.makeSocket()
1592 This is a factory method which allows subclasses to define the precise type of
1593 socket they want. The default implementation creates a TCP socket
1594 (:const:`socket.SOCK_STREAM`).
1597 .. method:: SocketHandler.makePickle(record)
1599 Pickles the record's attribute dictionary in binary format with a length prefix,
1600 and returns it ready for transmission across the socket.
1603 .. method:: SocketHandler.send(packet)
1605 Send a pickled string *packet* to the socket. This function allows for partial
1606 sends which can happen when the network is busy.
1612 The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1613 module, inherits from :class:`SocketHandler` to support sending logging messages
1617 .. class:: DatagramHandler(host, port)
1619 Returns a new instance of the :class:`DatagramHandler` class intended to
1620 communicate with a remote machine whose address is given by *host* and *port*.
1623 .. method:: DatagramHandler.emit()
1625 Pickles the record's attribute dictionary and writes it to the socket in binary
1626 format. If there is an error with the socket, silently drops the packet. To
1627 unpickle the record at the receiving end into a :class:`LogRecord`, use the
1628 :func:`makeLogRecord` function.
1631 .. method:: DatagramHandler.makeSocket()
1633 The factory method of :class:`SocketHandler` is here overridden to create a UDP
1634 socket (:const:`socket.SOCK_DGRAM`).
1637 .. method:: DatagramHandler.send(s)
1639 Send a pickled string to a socket.
1645 The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1646 supports sending logging messages to a remote or local Unix syslog.
1649 .. class:: SysLogHandler([address[, facility]])
1651 Returns a new instance of the :class:`SysLogHandler` class intended to
1652 communicate with a remote Unix machine whose address is given by *address* in
1653 the form of a ``(host, port)`` tuple. If *address* is not specified,
1654 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1655 alternative to providing a ``(host, port)`` tuple is providing an address as a
1656 string, for example "/dev/log". In this case, a Unix domain socket is used to
1657 send the message to the syslog. If *facility* is not specified,
1658 :const:`LOG_USER` is used.
1661 .. method:: SysLogHandler.close()
1663 Closes the socket to the remote host.
1666 .. method:: SysLogHandler.emit(record)
1668 The record is formatted, and then sent to the syslog server. If exception
1669 information is present, it is *not* sent to the server.
1672 .. method:: SysLogHandler.encodePriority(facility, priority)
1674 Encodes the facility and priority into an integer. You can pass in strings or
1675 integers - if strings are passed, internal mapping dictionaries are used to
1676 convert them to integers.
1682 The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1683 module, supports sending logging messages to a local Windows NT, Windows 2000 or
1684 Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1685 extensions for Python installed.
1688 .. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1690 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1691 used to define the application name as it appears in the event log. An
1692 appropriate registry entry is created using this name. The *dllname* should give
1693 the fully qualified pathname of a .dll or .exe which contains message
1694 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1695 - this is installed with the Win32 extensions and contains some basic
1696 placeholder message definitions. Note that use of these placeholders will make
1697 your event logs big, as the entire message source is held in the log. If you
1698 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1699 contains the message definitions you want to use in the event log). The
1700 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1701 defaults to ``'Application'``.
1704 .. method:: NTEventLogHandler.close()
1706 At this point, you can remove the application name from the registry as a source
1707 of event log entries. However, if you do this, you will not be able to see the
1708 events as you intended in the Event Log Viewer - it needs to be able to access
1709 the registry to get the .dll name. The current version does not do this (in fact
1710 it doesn't do anything).
1713 .. method:: NTEventLogHandler.emit(record)
1715 Determines the message ID, event category and event type, and then logs the
1716 message in the NT event log.
1719 .. method:: NTEventLogHandler.getEventCategory(record)
1721 Returns the event category for the record. Override this if you want to specify
1722 your own categories. This version returns 0.
1725 .. method:: NTEventLogHandler.getEventType(record)
1727 Returns the event type for the record. Override this if you want to specify your
1728 own types. This version does a mapping using the handler's typemap attribute,
1729 which is set up in :meth:`__init__` to a dictionary which contains mappings for
1730 :const:`DEBUG`, :const:`INFO`, :const:`WARNING`, :const:`ERROR` and
1731 :const:`CRITICAL`. If you are using your own levels, you will either need to
1732 override this method or place a suitable dictionary in the handler's *typemap*
1736 .. method:: NTEventLogHandler.getMessageID(record)
1738 Returns the message ID for the record. If you are using your own messages, you
1739 could do this by having the *msg* passed to the logger being an ID rather than a
1740 format string. Then, in here, you could use a dictionary lookup to get the
1741 message ID. This version returns 1, which is the base message ID in
1742 :file:`win32service.pyd`.
1748 The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1749 supports sending logging messages to an email address via SMTP.
1752 .. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1754 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1755 initialized with the from and to addresses and subject line of the email. The
1756 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1757 the (host, port) tuple format for the *mailhost* argument. If you use a string,
1758 the standard SMTP port is used. If your SMTP server requires authentication, you
1759 can specify a (username, password) tuple for the *credentials* argument.
1761 .. versionchanged:: 2.6
1762 *credentials* was added.
1765 .. method:: SMTPHandler.emit(record)
1767 Formats the record and sends it to the specified addressees.
1770 .. method:: SMTPHandler.getSubject(record)
1772 If you want to specify a subject line which is record-dependent, override this
1779 The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
1780 supports buffering of logging records in memory, periodically flushing them to a
1781 :dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
1782 event of a certain severity or greater is seen.
1784 :class:`MemoryHandler` is a subclass of the more general
1785 :class:`BufferingHandler`, which is an abstract class. This buffers logging
1786 records in memory. Whenever each record is added to the buffer, a check is made
1787 by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
1788 should, then :meth:`flush` is expected to do the needful.
1791 .. class:: BufferingHandler(capacity)
1793 Initializes the handler with a buffer of the specified capacity.
1796 .. method:: BufferingHandler.emit(record)
1798 Appends the record to the buffer. If :meth:`shouldFlush` returns true, calls
1799 :meth:`flush` to process the buffer.
1802 .. method:: BufferingHandler.flush()
1804 You can override this to implement custom flushing behavior. This version just
1805 zaps the buffer to empty.
1808 .. method:: BufferingHandler.shouldFlush(record)
1810 Returns true if the buffer is up to capacity. This method can be overridden to
1811 implement custom flushing strategies.
1814 .. class:: MemoryHandler(capacity[, flushLevel [, target]])
1816 Returns a new instance of the :class:`MemoryHandler` class. The instance is
1817 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
1818 :const:`ERROR` is used. If no *target* is specified, the target will need to be
1819 set using :meth:`setTarget` before this handler does anything useful.
1822 .. method:: MemoryHandler.close()
1824 Calls :meth:`flush`, sets the target to :const:`None` and clears the buffer.
1827 .. method:: MemoryHandler.flush()
1829 For a :class:`MemoryHandler`, flushing means just sending the buffered records
1830 to the target, if there is one. Override if you want different behavior.
1833 .. method:: MemoryHandler.setTarget(target)
1835 Sets the target handler for this handler.
1838 .. method:: MemoryHandler.shouldFlush(record)
1840 Checks for buffer full or a record at the *flushLevel* or higher.
1846 The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
1847 supports sending logging messages to a Web server, using either ``GET`` or
1851 .. class:: HTTPHandler(host, url[, method])
1853 Returns a new instance of the :class:`HTTPHandler` class. The instance is
1854 initialized with a host address, url and HTTP method. The *host* can be of the
1855 form ``host:port``, should you need to use a specific port number. If no
1856 *method* is specified, ``GET`` is used.
1859 .. method:: HTTPHandler.emit(record)
1861 Sends the record to the Web server as an URL-encoded dictionary.
1864 .. _formatter-objects:
1869 :class:`Formatter`\ s have the following attributes and methods. They are
1870 responsible for converting a :class:`LogRecord` to (usually) a string which can
1871 be interpreted by either a human or an external system. The base
1872 :class:`Formatter` allows a formatting string to be specified. If none is
1873 supplied, the default value of ``'%(message)s'`` is used.
1875 A Formatter can be initialized with a format string which makes use of knowledge
1876 of the :class:`LogRecord` attributes - such as the default value mentioned above
1877 making use of the fact that the user's message and arguments are pre-formatted
1878 into a :class:`LogRecord`'s *message* attribute. This format string contains
1879 standard python %-style mapping keys. See section :ref:`string-formatting`
1880 for more information on string formatting.
1882 Currently, the useful mapping keys in a :class:`LogRecord` are:
1884 +-------------------------+-----------------------------------------------+
1885 | Format | Description |
1886 +=========================+===============================================+
1887 | ``%(name)s`` | Name of the logger (logging channel). |
1888 +-------------------------+-----------------------------------------------+
1889 | ``%(levelno)s`` | Numeric logging level for the message |
1890 | | (:const:`DEBUG`, :const:`INFO`, |
1891 | | :const:`WARNING`, :const:`ERROR`, |
1892 | | :const:`CRITICAL`). |
1893 +-------------------------+-----------------------------------------------+
1894 | ``%(levelname)s`` | Text logging level for the message |
1895 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1896 | | ``'ERROR'``, ``'CRITICAL'``). |
1897 +-------------------------+-----------------------------------------------+
1898 | ``%(pathname)s`` | Full pathname of the source file where the |
1899 | | logging call was issued (if available). |
1900 +-------------------------+-----------------------------------------------+
1901 | ``%(filename)s`` | Filename portion of pathname. |
1902 +-------------------------+-----------------------------------------------+
1903 | ``%(module)s`` | Module (name portion of filename). |
1904 +-------------------------+-----------------------------------------------+
1905 | ``%(funcName)s`` | Name of function containing the logging call. |
1906 +-------------------------+-----------------------------------------------+
1907 | ``%(lineno)d`` | Source line number where the logging call was |
1908 | | issued (if available). |
1909 +-------------------------+-----------------------------------------------+
1910 | ``%(created)f`` | Time when the :class:`LogRecord` was created |
1911 | | (as returned by :func:`time.time`). |
1912 +-------------------------+-----------------------------------------------+
1913 | ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
1914 | | created, relative to the time the logging |
1915 | | module was loaded. |
1916 +-------------------------+-----------------------------------------------+
1917 | ``%(asctime)s`` | Human-readable time when the |
1918 | | :class:`LogRecord` was created. By default |
1919 | | this is of the form "2003-07-08 16:49:45,896" |
1920 | | (the numbers after the comma are millisecond |
1921 | | portion of the time). |
1922 +-------------------------+-----------------------------------------------+
1923 | ``%(msecs)d`` | Millisecond portion of the time when the |
1924 | | :class:`LogRecord` was created. |
1925 +-------------------------+-----------------------------------------------+
1926 | ``%(thread)d`` | Thread ID (if available). |
1927 +-------------------------+-----------------------------------------------+
1928 | ``%(threadName)s`` | Thread name (if available). |
1929 +-------------------------+-----------------------------------------------+
1930 | ``%(process)d`` | Process ID (if available). |
1931 +-------------------------+-----------------------------------------------+
1932 | ``%(message)s`` | The logged message, computed as ``msg % |
1934 +-------------------------+-----------------------------------------------+
1936 .. versionchanged:: 2.5
1937 *funcName* was added.
1940 .. class:: Formatter([fmt[, datefmt]])
1942 Returns a new instance of the :class:`Formatter` class. The instance is
1943 initialized with a format string for the message as a whole, as well as a format
1944 string for the date/time portion of a message. If no *fmt* is specified,
1945 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
1949 .. method:: Formatter.format(record)
1951 The record's attribute dictionary is used as the operand to a string formatting
1952 operation. Returns the resulting string. Before formatting the dictionary, a
1953 couple of preparatory steps are carried out. The *message* attribute of the
1954 record is computed using *msg* % *args*. If the formatting string contains
1955 ``'(asctime)'``, :meth:`formatTime` is called to format the event time. If there
1956 is exception information, it is formatted using :meth:`formatException` and
1957 appended to the message.
1960 .. method:: Formatter.formatTime(record[, datefmt])
1962 This method should be called from :meth:`format` by a formatter which wants to
1963 make use of a formatted time. This method can be overridden in formatters to
1964 provide for any specific requirement, but the basic behavior is as follows: if
1965 *datefmt* (a string) is specified, it is used with :func:`time.strftime` to
1966 format the creation time of the record. Otherwise, the ISO8601 format is used.
1967 The resulting string is returned.
1970 .. method:: Formatter.formatException(exc_info)
1972 Formats the specified exception information (a standard exception tuple as
1973 returned by :func:`sys.exc_info`) as a string. This default implementation just
1974 uses :func:`traceback.print_exception`. The resulting string is returned.
1980 :class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
1981 more sophisticated filtering than is provided by levels. The base filter class
1982 only allows events which are below a certain point in the logger hierarchy. For
1983 example, a filter initialized with "A.B" will allow events logged by loggers
1984 "A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
1985 initialized with the empty string, all events are passed.
1988 .. class:: Filter([name])
1990 Returns an instance of the :class:`Filter` class. If *name* is specified, it
1991 names a logger which, together with its children, will have its events allowed
1992 through the filter. If no name is specified, allows every event.
1995 .. method:: Filter.filter(record)
1997 Is the specified record to be logged? Returns zero for no, nonzero for yes. If
1998 deemed appropriate, the record may be modified in-place by this method.
2004 :class:`LogRecord` instances are created every time something is logged. They
2005 contain all the information pertinent to the event being logged. The main
2006 information passed in is in msg and args, which are combined using msg % args to
2007 create the message field of the record. The record also includes information
2008 such as when the record was created, the source line where the logging call was
2009 made, and any exception information to be logged.
2012 .. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2014 Returns an instance of :class:`LogRecord` initialized with interesting
2015 information. The *name* is the logger name; *lvl* is the numeric level;
2016 *pathname* is the absolute pathname of the source file in which the logging
2017 call was made; *lineno* is the line number in that file where the logging
2018 call is found; *msg* is the user-supplied message (a format string); *args*
2019 is the tuple which, together with *msg*, makes up the user message; and
2020 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2021 (or :const:`None`, if no exception information is available). The *func* is
2022 the name of the function from which the logging call was made. If not
2023 specified, it defaults to ``None``.
2025 .. versionchanged:: 2.5
2029 .. method:: LogRecord.getMessage()
2031 Returns the message for this :class:`LogRecord` instance after merging any
2032 user-supplied arguments with the message.
2038 The logging module is intended to be thread-safe without any special work
2039 needing to be done by its clients. It achieves this though using threading
2040 locks; there is one lock to serialize access to the module's shared data, and
2041 each handler also creates a lock to serialize access to its underlying I/O.
2048 .. _logging-config-api:
2050 Configuration functions
2051 ^^^^^^^^^^^^^^^^^^^^^^^
2053 The following functions configure the logging module. They are located in the
2054 :mod:`logging.config` module. Their use is optional --- you can configure the
2055 logging module using these functions or by making calls to the main API (defined
2056 in :mod:`logging` itself) and defining handlers which are declared either in
2057 :mod:`logging` or :mod:`logging.handlers`.
2060 .. function:: fileConfig(fname[, defaults])
2062 Reads the logging configuration from a ConfigParser-format file named *fname*.
2063 This function can be called several times from an application, allowing an end
2064 user the ability to select from various pre-canned configurations (if the
2065 developer provides a mechanism to present the choices and load the chosen
2066 configuration). Defaults to be passed to ConfigParser can be specified in the
2067 *defaults* argument.
2070 .. function:: listen([port])
2072 Starts up a socket server on the specified port, and listens for new
2073 configurations. If no port is specified, the module's default
2074 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2075 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2076 :class:`Thread` instance on which you can call :meth:`start` to start the
2077 server, and which you can :meth:`join` when appropriate. To stop the server,
2078 call :func:`stopListening`.
2080 To send a configuration to the socket, read in the configuration file and
2081 send it to the socket as a string of bytes preceded by a four-byte length
2082 string packed in binary using ``struct.pack('>L', n)``.
2085 .. function:: stopListening()
2087 Stops the listening server which was created with a call to :func:`listen`.
2088 This is typically called before calling :meth:`join` on the return value from
2092 .. _logging-config-fileformat:
2094 Configuration file format
2095 ^^^^^^^^^^^^^^^^^^^^^^^^^
2097 The configuration file format understood by :func:`fileConfig` is based on
2098 ConfigParser functionality. The file must contain sections called ``[loggers]``,
2099 ``[handlers]`` and ``[formatters]`` which identify by name the entities of each
2100 type which are defined in the file. For each such entity, there is a separate
2101 section which identified how that entity is configured. Thus, for a logger named
2102 ``log01`` in the ``[loggers]`` section, the relevant configuration details are
2103 held in a section ``[logger_log01]``. Similarly, a handler called ``hand01`` in
2104 the ``[handlers]`` section will have its configuration held in a section called
2105 ``[handler_hand01]``, while a formatter called ``form01`` in the
2106 ``[formatters]`` section will have its configuration specified in a section
2107 called ``[formatter_form01]``. The root logger configuration must be specified
2108 in a section called ``[logger_root]``.
2110 Examples of these sections in the file are given below. ::
2113 keys=root,log02,log03,log04,log05,log06,log07
2116 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2119 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2121 The root logger must specify a level and a list of handlers. An example of a
2122 root logger section is given below. ::
2128 The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2129 ``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2130 logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2131 package's namespace.
2133 The ``handlers`` entry is a comma-separated list of handler names, which must
2134 appear in the ``[handlers]`` section. These names must appear in the
2135 ``[handlers]`` section and have corresponding sections in the configuration
2138 For loggers other than the root logger, some additional information is required.
2139 This is illustrated by the following example. ::
2145 qualname=compiler.parser
2147 The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2148 except that if a non-root logger's level is specified as ``NOTSET``, the system
2149 consults loggers higher up the hierarchy to determine the effective level of the
2150 logger. The ``propagate`` entry is set to 1 to indicate that messages must
2151 propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2152 indicate that messages are **not** propagated to handlers up the hierarchy. The
2153 ``qualname`` entry is the hierarchical channel name of the logger, that is to
2154 say the name used by the application to get the logger.
2156 Sections which specify handler configuration are exemplified by the following.
2165 The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2166 in the ``logging`` package's namespace). The ``level`` is interpreted as for
2167 loggers, and ``NOTSET`` is taken to mean "log everything".
2169 The ``formatter`` entry indicates the key name of the formatter for this
2170 handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2171 If a name is specified, it must appear in the ``[formatters]`` section and have
2172 a corresponding section in the configuration file.
2174 The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2175 package's namespace, is the list of arguments to the constructor for the handler
2176 class. Refer to the constructors for the relevant handlers, or to the examples
2177 below, to see how typical entries are constructed. ::
2183 args=('python.log', 'w')
2186 class=handlers.SocketHandler
2189 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2192 class=handlers.DatagramHandler
2195 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2198 class=handlers.SysLogHandler
2201 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2204 class=handlers.NTEventLogHandler
2207 args=('Python Application', '', 'Application')
2210 class=handlers.SMTPHandler
2213 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2216 class=handlers.MemoryHandler
2223 class=handlers.HTTPHandler
2226 args=('localhost:9022', '/log', 'GET')
2228 Sections which specify formatter configuration are typified by the following. ::
2231 format=F1 %(asctime)s %(levelname)s %(message)s
2233 class=logging.Formatter
2235 The ``format`` entry is the overall format string, and the ``datefmt`` entry is
2236 the :func:`strftime`\ -compatible date/time format string. If empty, the
2237 package substitutes ISO8601 format date/times, which is almost equivalent to
2238 specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2239 also specifies milliseconds, which are appended to the result of using the above
2240 format string, with a comma separator. An example time in ISO8601 format is
2241 ``2003-01-23 00:29:50,411``.
2243 The ``class`` entry is optional. It indicates the name of the formatter's class
2244 (as a dotted module and class name.) This option is useful for instantiating a
2245 :class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2246 exception tracebacks in an expanded or condensed format.
2249 Configuration server example
2250 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2252 Here is an example of a module using the logging configuration server::
2255 import logging.config
2259 # read initial config file
2260 logging.config.fileConfig("logging.conf")
2262 # create and start listener on port 9999
2263 t = logging.config.listen(9999)
2266 logger = logging.getLogger("simpleExample")
2269 # loop through logging calls to see the difference
2270 # new configurations make, until Ctrl+C is pressed
2272 logger.debug("debug message")
2273 logger.info("info message")
2274 logger.warn("warn message")
2275 logger.error("error message")
2276 logger.critical("critical message")
2278 except KeyboardInterrupt:
2280 logging.config.stopListening()
2283 And here is a script that takes a filename and sends that file to the server,
2284 properly preceded with the binary-encoded length, as the new logging
2287 #!/usr/bin/env python
2288 import socket, sys, struct
2290 data_to_send = open(sys.argv[1], "r").read()
2294 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2295 print "connecting..."
2296 s.connect((HOST, PORT))
2297 print "sending config..."
2298 s.send(struct.pack(">L", len(data_to_send)))
2299 s.send(data_to_send)
2307 Multiple handlers and formatters
2308 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2310 Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2311 or maximum quota for the number of handlers you may add. Sometimes it will be
2312 beneficial for an application to log all messages of all severities to a text
2313 file while simultaneously logging errors or above to the console. To set this
2314 up, simply configure the appropriate handlers. The logging calls in the
2315 application code will remain unchanged. Here is a slight modification to the
2316 previous simple module-based configuration example::
2320 logger = logging.getLogger("simple_example")
2321 logger.setLevel(logging.DEBUG)
2322 # create file handler which logs even debug messages
2323 fh = logging.FileHandler("spam.log")
2324 fh.setLevel(logging.DEBUG)
2325 # create console handler with a higher log level
2326 ch = logging.StreamHandler()
2327 ch.setLevel(logging.ERROR)
2328 # create formatter and add it to the handlers
2329 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2330 ch.setFormatter(formatter)
2331 fh.setFormatter(formatter)
2332 # add the handlers to logger
2333 logger.addHandler(ch)
2334 logger.addHandler(fh)
2336 # "application" code
2337 logger.debug("debug message")
2338 logger.info("info message")
2339 logger.warn("warn message")
2340 logger.error("error message")
2341 logger.critical("critical message")
2343 Notice that the "application" code does not care about multiple handlers. All
2344 that changed was the addition and configuration of a new handler named *fh*.
2346 The ability to create new handlers with higher- or lower-severity filters can be
2347 very helpful when writing and testing an application. Instead of using many
2348 ``print`` statements for debugging, use ``logger.debug``: Unlike the print
2349 statements, which you will have to delete or comment out later, the logger.debug
2350 statements can remain intact in the source code and remain dormant until you
2351 need them again. At that time, the only change that needs to happen is to
2352 modify the severity level of the logger and/or handler to debug.
2355 Using logging in multiple modules
2356 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2358 It was mentioned above that multiple calls to
2359 ``logging.getLogger('someLogger')`` return a reference to the same logger
2360 object. This is true not only within the same module, but also across modules
2361 as long as it is in the same Python interpreter process. It is true for
2362 references to the same object; additionally, application code can define and
2363 configure a parent logger in one module and create (but not configure) a child
2364 logger in a separate module, and all logger calls to the child will pass up to
2365 the parent. Here is a main module::
2368 import auxiliary_module
2370 # create logger with "spam_application"
2371 logger = logging.getLogger("spam_application")
2372 logger.setLevel(logging.DEBUG)
2373 # create file handler which logs even debug messages
2374 fh = logging.FileHandler("spam.log")
2375 fh.setLevel(logging.DEBUG)
2376 # create console handler with a higher log level
2377 ch = logging.StreamHandler()
2378 ch.setLevel(logging.ERROR)
2379 # create formatter and add it to the handlers
2380 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2381 fh.setFormatter(formatter)
2382 ch.setFormatter(formatter)
2383 # add the handlers to the logger
2384 logger.addHandler(fh)
2385 logger.addHandler(ch)
2387 logger.info("creating an instance of auxiliary_module.Auxiliary")
2388 a = auxiliary_module.Auxiliary()
2389 logger.info("created an instance of auxiliary_module.Auxiliary")
2390 logger.info("calling auxiliary_module.Auxiliary.do_something")
2392 logger.info("finished auxiliary_module.Auxiliary.do_something")
2393 logger.info("calling auxiliary_module.some_function()")
2394 auxiliary_module.some_function()
2395 logger.info("done with auxiliary_module.some_function()")
2397 Here is the auxiliary module::
2402 module_logger = logging.getLogger("spam_application.auxiliary")
2406 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2407 self.logger.info("creating an instance of Auxiliary")
2408 def do_something(self):
2409 self.logger.info("doing something")
2411 self.logger.info("done doing something")
2413 def some_function():
2414 module_logger.info("received a call to \"some_function\"")
2416 The output looks like this::
2418 2005-03-23 23:47:11,663 - spam_application - INFO -
2419 creating an instance of auxiliary_module.Auxiliary
2420 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
2421 creating an instance of Auxiliary
2422 2005-03-23 23:47:11,665 - spam_application - INFO -
2423 created an instance of auxiliary_module.Auxiliary
2424 2005-03-23 23:47:11,668 - spam_application - INFO -
2425 calling auxiliary_module.Auxiliary.do_something
2426 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
2428 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
2429 done doing something
2430 2005-03-23 23:47:11,670 - spam_application - INFO -
2431 finished auxiliary_module.Auxiliary.do_something
2432 2005-03-23 23:47:11,671 - spam_application - INFO -
2433 calling auxiliary_module.some_function()
2434 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
2435 received a call to "some_function"
2436 2005-03-23 23:47:11,673 - spam_application - INFO -
2437 done with auxiliary_module.some_function()