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.
1142 Adding contextual information to your logging output
1143 ----------------------------------------------------
1145 Sometimes you want logging output to contain contextual information in
1146 addition to the parameters passed to the logging call. For example, in a
1147 networked application, it may be desirable to log client-specific information
1148 in the log (e.g. remote client's username, or IP address). Although you could
1149 use the *extra* parameter to achieve this, it's not always convenient to pass
1150 the information in this way. While it might be tempting to create
1151 :class:`Logger` instances on a per-connection basis, this is not a good idea
1152 because these instances are not garbage collected. While this is not a problem
1153 in practice, when the number of :class:`Logger` instances is dependent on the
1154 level of granularity you want to use in logging an application, it could
1155 be hard to manage if the number of :class:`Logger` instances becomes
1156 effectively unbounded.
1158 An easy way in which you can pass contextual information to be output along
1159 with logging event information is to use the :class:`LoggerAdapter` class.
1160 This class is designed to look like a :class:`Logger`, so that you can call
1161 :meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
1162 :meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
1163 same signatures as their counterparts in :class:`Logger`, so you can use the
1164 two types of instances interchangeably.
1166 When you create an instance of :class:`LoggerAdapter`, you pass it a
1167 :class:`Logger` instance and a dict-like object which contains your contextual
1168 information. When you call one of the logging methods on an instance of
1169 :class:`LoggerAdapter`, it delegates the call to the underlying instance of
1170 :class:`Logger` passed to its constructor, and arranges to pass the contextual
1171 information in the delegated call. Here's a snippet from the code of
1172 :class:`LoggerAdapter`::
1174 def debug(self, msg, *args, **kwargs):
1176 Delegate a debug call to the underlying logger, after adding
1177 contextual information from this adapter instance.
1179 msg, kwargs = self.process(msg, kwargs)
1180 self.logger.debug(msg, *args, **kwargs)
1182 The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
1183 information is added to the logging output. It's passed the message and
1184 keyword arguments of the logging call, and it passes back (potentially)
1185 modified versions of these to use in the call to the underlying logger. The
1186 default implementation of this method leaves the message alone, but inserts
1187 an "extra" key in the keyword argument whose value is the dict-like object
1188 passed to the constructor. Of course, if you had passed an "extra" keyword
1189 argument in the call to the adapter, it will be silently overwritten.
1191 The advantage of using "extra" is that the values in the dict-like object are
1192 merged into the :class:`LogRecord` instance's __dict__, allowing you to use
1193 customized strings with your :class:`Formatter` instances which know about
1194 the keys of the dict-like object. If you need a different method, e.g. if you
1195 want to prepend or append the contextual information to the message string,
1196 you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
1197 to do what you need. Here's an example script which uses this class, which
1198 also illustrates what dict-like behaviour is needed from an arbitrary
1199 "dict-like" object for use in the constructor::
1205 An example class which shows how an arbitrary class can be used as
1206 the 'extra' context information repository passed to a LoggerAdapter.
1209 def __getitem__(self, name):
1211 To allow this instance to look like a dict.
1213 from random import choice
1215 result = choice(["127.0.0.1", "192.168.0.1"])
1216 elif name == "user":
1217 result = choice(["jim", "fred", "sheila"])
1219 result = self.__dict__.get(name, "?")
1224 To allow iteration over keys, which will be merged into
1225 the LogRecord dict before formatting and output.
1227 keys = ["ip", "user"]
1228 keys.extend(self.__dict__.keys())
1229 return keys.__iter__()
1231 if __name__ == "__main__":
1232 from random import choice
1233 levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
1234 a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"),
1235 { "ip" : "123.231.231.123", "user" : "sheila" })
1236 logging.basicConfig(level=logging.DEBUG,
1237 format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s")
1238 a1.debug("A debug message")
1239 a1.info("An info message with %s", "some parameters")
1240 a2 = logging.LoggerAdapter(logging.getLogger("d.e.f"), ConnInfo())
1242 lvl = choice(levels)
1243 lvlname = logging.getLevelName(lvl)
1244 a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters")
1246 When this script is run, the output should look something like this::
1248 2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
1249 2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
1250 2008-01-18 14:49:54,023 d.e.f CRITICAL IP: 192.168.0.1 User: jim A message at CRITICAL level with 2 parameters
1251 2008-01-18 14:49:54,033 d.e.f INFO IP: 192.168.0.1 User: jim A message at INFO level with 2 parameters
1252 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1253 2008-01-18 14:49:54,033 d.e.f ERROR IP: 127.0.0.1 User: fred A message at ERROR level with 2 parameters
1254 2008-01-18 14:49:54,033 d.e.f ERROR IP: 127.0.0.1 User: sheila A message at ERROR level with 2 parameters
1255 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1256 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: jim A message at WARNING level with 2 parameters
1257 2008-01-18 14:49:54,033 d.e.f INFO IP: 192.168.0.1 User: fred A message at INFO level with 2 parameters
1258 2008-01-18 14:49:54,033 d.e.f WARNING IP: 192.168.0.1 User: sheila A message at WARNING level with 2 parameters
1259 2008-01-18 14:49:54,033 d.e.f WARNING IP: 127.0.0.1 User: jim A message at WARNING level with 2 parameters
1261 .. versionadded:: 2.6
1263 The :class:`LoggerAdapter` class was not present in previous versions.
1266 .. _network-logging:
1268 Sending and receiving logging events across a network
1269 -----------------------------------------------------
1271 Let's say you want to send logging events across a network, and handle them at
1272 the receiving end. A simple way of doing this is attaching a
1273 :class:`SocketHandler` instance to the root logger at the sending end::
1275 import logging, logging.handlers
1277 rootLogger = logging.getLogger('')
1278 rootLogger.setLevel(logging.DEBUG)
1279 socketHandler = logging.handlers.SocketHandler('localhost',
1280 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1281 # don't bother with a formatter, since a socket handler sends the event as
1282 # an unformatted pickle
1283 rootLogger.addHandler(socketHandler)
1285 # Now, we can log to the root logger, or any other logger. First the root...
1286 logging.info('Jackdaws love my big sphinx of quartz.')
1288 # Now, define a couple of other loggers which might represent areas in your
1291 logger1 = logging.getLogger('myapp.area1')
1292 logger2 = logging.getLogger('myapp.area2')
1294 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1295 logger1.info('How quickly daft jumping zebras vex.')
1296 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1297 logger2.error('The five boxing wizards jump quickly.')
1299 At the receiving end, you can set up a receiver using the :mod:`SocketServer`
1300 module. Here is a basic working example::
1304 import logging.handlers
1309 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
1310 """Handler for a streaming logging request.
1312 This basically logs the record using whatever logging policy is
1318 Handle multiple requests - each expected to be a 4-byte length,
1319 followed by the LogRecord in pickle format. Logs the record
1320 according to whatever policy is configured locally.
1323 chunk = self.connection.recv(4)
1326 slen = struct.unpack(">L", chunk)[0]
1327 chunk = self.connection.recv(slen)
1328 while len(chunk) < slen:
1329 chunk = chunk + self.connection.recv(slen - len(chunk))
1330 obj = self.unPickle(chunk)
1331 record = logging.makeLogRecord(obj)
1332 self.handleLogRecord(record)
1334 def unPickle(self, data):
1335 return cPickle.loads(data)
1337 def handleLogRecord(self, record):
1338 # if a name is specified, we use the named logger rather than the one
1339 # implied by the record.
1340 if self.server.logname is not None:
1341 name = self.server.logname
1344 logger = logging.getLogger(name)
1345 # N.B. EVERY record gets logged. This is because Logger.handle
1346 # is normally called AFTER logger-level filtering. If you want
1347 # to do filtering, do it at the client end to save wasting
1348 # cycles and network bandwidth!
1349 logger.handle(record)
1351 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
1352 """simple TCP socket-based logging receiver suitable for testing.
1355 allow_reuse_address = 1
1357 def __init__(self, host='localhost',
1358 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1359 handler=LogRecordStreamHandler):
1360 SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
1365 def serve_until_stopped(self):
1369 rd, wr, ex = select.select([self.socket.fileno()],
1373 self.handle_request()
1377 logging.basicConfig(
1378 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1379 tcpserver = LogRecordSocketReceiver()
1380 print "About to start TCP server..."
1381 tcpserver.serve_until_stopped()
1383 if __name__ == "__main__":
1386 First run the server, and then the client. On the client side, nothing is
1387 printed on the console; on the server side, you should see something like::
1389 About to start TCP server...
1390 59 root INFO Jackdaws love my big sphinx of quartz.
1391 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1392 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1393 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1394 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1400 Handlers have the following attributes and methods. Note that :class:`Handler`
1401 is never instantiated directly; this class acts as a base for more useful
1402 subclasses. However, the :meth:`__init__` method in subclasses needs to call
1403 :meth:`Handler.__init__`.
1406 .. method:: Handler.__init__(level=NOTSET)
1408 Initializes the :class:`Handler` instance by setting its level, setting the list
1409 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1410 serializing access to an I/O mechanism.
1413 .. method:: Handler.createLock()
1415 Initializes a thread lock which can be used to serialize access to underlying
1416 I/O functionality which may not be threadsafe.
1419 .. method:: Handler.acquire()
1421 Acquires the thread lock created with :meth:`createLock`.
1424 .. method:: Handler.release()
1426 Releases the thread lock acquired with :meth:`acquire`.
1429 .. method:: Handler.setLevel(lvl)
1431 Sets the threshold for this handler to *lvl*. Logging messages which are less
1432 severe than *lvl* will be ignored. When a handler is created, the level is set
1433 to :const:`NOTSET` (which causes all messages to be processed).
1436 .. method:: Handler.setFormatter(form)
1438 Sets the :class:`Formatter` for this handler to *form*.
1441 .. method:: Handler.addFilter(filt)
1443 Adds the specified filter *filt* to this handler.
1446 .. method:: Handler.removeFilter(filt)
1448 Removes the specified filter *filt* from this handler.
1451 .. method:: Handler.filter(record)
1453 Applies this handler's filters to the record and returns a true value if the
1454 record is to be processed.
1457 .. method:: Handler.flush()
1459 Ensure all logging output has been flushed. This version does nothing and is
1460 intended to be implemented by subclasses.
1463 .. method:: Handler.close()
1465 Tidy up any resources used by the handler. This version does nothing and is
1466 intended to be implemented by subclasses.
1469 .. method:: Handler.handle(record)
1471 Conditionally emits the specified logging record, depending on filters which may
1472 have been added to the handler. Wraps the actual emission of the record with
1473 acquisition/release of the I/O thread lock.
1476 .. method:: Handler.handleError(record)
1478 This method should be called from handlers when an exception is encountered
1479 during an :meth:`emit` call. By default it does nothing, which means that
1480 exceptions get silently ignored. This is what is mostly wanted for a logging
1481 system - most users will not care about errors in the logging system, they are
1482 more interested in application errors. You could, however, replace this with a
1483 custom handler if you wish. The specified record is the one which was being
1484 processed when the exception occurred.
1487 .. method:: Handler.format(record)
1489 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1490 default formatter for the module.
1493 .. method:: Handler.emit(record)
1495 Do whatever it takes to actually log the specified logging record. This version
1496 is intended to be implemented by subclasses and so raises a
1497 :exc:`NotImplementedError`.
1503 The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1504 sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1505 file-like object (or, more precisely, any object which supports :meth:`write`
1506 and :meth:`flush` methods).
1509 .. class:: StreamHandler([strm])
1511 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1512 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1516 .. method:: StreamHandler.emit(record)
1518 If a formatter is specified, it is used to format the record. The record is then
1519 written to the stream with a trailing newline. If exception information is
1520 present, it is formatted using :func:`traceback.print_exception` and appended to
1524 .. method:: StreamHandler.flush()
1526 Flushes the stream by calling its :meth:`flush` method. Note that the
1527 :meth:`close` method is inherited from :class:`Handler` and so does nothing, so
1528 an explicit :meth:`flush` call may be needed at times.
1534 The :class:`FileHandler` class, located in the core :mod:`logging` package,
1535 sends logging output to a disk file. It inherits the output functionality from
1536 :class:`StreamHandler`.
1539 .. class:: FileHandler(filename[, mode[, encoding]])
1541 Returns a new instance of the :class:`FileHandler` class. The specified file is
1542 opened and used as the stream for logging. If *mode* is not specified,
1543 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1544 with that encoding. By default, the file grows indefinitely.
1547 .. method:: FileHandler.close()
1552 .. method:: FileHandler.emit(record)
1554 Outputs the record to the file.
1560 .. versionadded:: 2.6
1562 The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1563 module, is a :class:`FileHandler` which watches the file it is logging to. If
1564 the file changes, it is closed and reopened using the file name.
1566 A file change can happen because of usage of programs such as *newsyslog* and
1567 *logrotate* which perform log file rotation. This handler, intended for use
1568 under Unix/Linux, watches the file to see if it has changed since the last emit.
1569 (A file is deemed to have changed if its device or inode have changed.) If the
1570 file has changed, the old file stream is closed, and the file opened to get a
1573 This handler is not appropriate for use under Windows, because under Windows
1574 open log files cannot be moved or renamed - logging opens the files with
1575 exclusive locks - and so there is no need for such a handler. Furthermore,
1576 *ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1580 .. class:: WatchedFileHandler(filename[,mode[, encoding]])
1582 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1583 file is opened and used as the stream for logging. If *mode* is not specified,
1584 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1585 with that encoding. By default, the file grows indefinitely.
1588 .. method:: WatchedFileHandler.emit(record)
1590 Outputs the record to the file, but first checks to see if the file has changed.
1591 If it has, the existing stream is flushed and closed and the file opened again,
1592 before outputting the record to the file.
1598 The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1599 module, supports rotation of disk log files.
1602 .. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount]]])
1604 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1605 file is opened and used as the stream for logging. If *mode* is not specified,
1606 ``'a'`` is used. By default, the file grows indefinitely.
1608 You can use the *maxBytes* and *backupCount* values to allow the file to
1609 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1610 the file is closed and a new file is silently opened for output. Rollover occurs
1611 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1612 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1613 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1614 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1615 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1616 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1617 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1618 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1619 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1622 .. method:: RotatingFileHandler.doRollover()
1624 Does a rollover, as described above.
1627 .. method:: RotatingFileHandler.emit(record)
1629 Outputs the record to the file, catering for rollover as described previously.
1632 TimedRotatingFileHandler
1633 ^^^^^^^^^^^^^^^^^^^^^^^^
1635 The :class:`TimedRotatingFileHandler` class, located in the
1636 :mod:`logging.handlers` module, supports rotation of disk log files at certain
1640 .. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount]]])
1642 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1643 specified file is opened and used as the stream for logging. On rotating it also
1644 sets the filename suffix. Rotating happens based on the product of *when* and
1647 You can use the *when* to specify the type of *interval*. The list of possible
1648 values is, note that they are not case sensitive:
1650 +----------+-----------------------+
1651 | Value | Type of interval |
1652 +==========+=======================+
1654 +----------+-----------------------+
1656 +----------+-----------------------+
1658 +----------+-----------------------+
1660 +----------+-----------------------+
1661 | W | Week day (0=Monday) |
1662 +----------+-----------------------+
1663 | midnight | Roll over at midnight |
1664 +----------+-----------------------+
1666 If *backupCount* is non-zero, the system will save old log files by appending
1667 extensions to the filename. The extensions are date-and-time based, using the
1668 strftime format ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on
1669 the rollover interval. At most *backupCount* files will be kept, and if more
1670 would be created when rollover occurs, the oldest one is deleted.
1673 .. method:: TimedRotatingFileHandler.doRollover()
1675 Does a rollover, as described above.
1678 .. method:: TimedRotatingFileHandler.emit(record)
1680 Outputs the record to the file, catering for rollover as described above.
1686 The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1687 sends logging output to a network socket. The base class uses a TCP socket.
1690 .. class:: SocketHandler(host, port)
1692 Returns a new instance of the :class:`SocketHandler` class intended to
1693 communicate with a remote machine whose address is given by *host* and *port*.
1696 .. method:: SocketHandler.close()
1701 .. method:: SocketHandler.emit()
1703 Pickles the record's attribute dictionary and writes it to the socket in binary
1704 format. If there is an error with the socket, silently drops the packet. If the
1705 connection was previously lost, re-establishes the connection. To unpickle the
1706 record at the receiving end into a :class:`LogRecord`, use the
1707 :func:`makeLogRecord` function.
1710 .. method:: SocketHandler.handleError()
1712 Handles an error which has occurred during :meth:`emit`. The most likely cause
1713 is a lost connection. Closes the socket so that we can retry on the next event.
1716 .. method:: SocketHandler.makeSocket()
1718 This is a factory method which allows subclasses to define the precise type of
1719 socket they want. The default implementation creates a TCP socket
1720 (:const:`socket.SOCK_STREAM`).
1723 .. method:: SocketHandler.makePickle(record)
1725 Pickles the record's attribute dictionary in binary format with a length prefix,
1726 and returns it ready for transmission across the socket.
1729 .. method:: SocketHandler.send(packet)
1731 Send a pickled string *packet* to the socket. This function allows for partial
1732 sends which can happen when the network is busy.
1738 The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1739 module, inherits from :class:`SocketHandler` to support sending logging messages
1743 .. class:: DatagramHandler(host, port)
1745 Returns a new instance of the :class:`DatagramHandler` class intended to
1746 communicate with a remote machine whose address is given by *host* and *port*.
1749 .. method:: DatagramHandler.emit()
1751 Pickles the record's attribute dictionary and writes it to the socket in binary
1752 format. If there is an error with the socket, silently drops the packet. To
1753 unpickle the record at the receiving end into a :class:`LogRecord`, use the
1754 :func:`makeLogRecord` function.
1757 .. method:: DatagramHandler.makeSocket()
1759 The factory method of :class:`SocketHandler` is here overridden to create a UDP
1760 socket (:const:`socket.SOCK_DGRAM`).
1763 .. method:: DatagramHandler.send(s)
1765 Send a pickled string to a socket.
1771 The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1772 supports sending logging messages to a remote or local Unix syslog.
1775 .. class:: SysLogHandler([address[, facility]])
1777 Returns a new instance of the :class:`SysLogHandler` class intended to
1778 communicate with a remote Unix machine whose address is given by *address* in
1779 the form of a ``(host, port)`` tuple. If *address* is not specified,
1780 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1781 alternative to providing a ``(host, port)`` tuple is providing an address as a
1782 string, for example "/dev/log". In this case, a Unix domain socket is used to
1783 send the message to the syslog. If *facility* is not specified,
1784 :const:`LOG_USER` is used.
1787 .. method:: SysLogHandler.close()
1789 Closes the socket to the remote host.
1792 .. method:: SysLogHandler.emit(record)
1794 The record is formatted, and then sent to the syslog server. If exception
1795 information is present, it is *not* sent to the server.
1798 .. method:: SysLogHandler.encodePriority(facility, priority)
1800 Encodes the facility and priority into an integer. You can pass in strings or
1801 integers - if strings are passed, internal mapping dictionaries are used to
1802 convert them to integers.
1808 The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1809 module, supports sending logging messages to a local Windows NT, Windows 2000 or
1810 Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1811 extensions for Python installed.
1814 .. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1816 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1817 used to define the application name as it appears in the event log. An
1818 appropriate registry entry is created using this name. The *dllname* should give
1819 the fully qualified pathname of a .dll or .exe which contains message
1820 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1821 - this is installed with the Win32 extensions and contains some basic
1822 placeholder message definitions. Note that use of these placeholders will make
1823 your event logs big, as the entire message source is held in the log. If you
1824 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1825 contains the message definitions you want to use in the event log). The
1826 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1827 defaults to ``'Application'``.
1830 .. method:: NTEventLogHandler.close()
1832 At this point, you can remove the application name from the registry as a source
1833 of event log entries. However, if you do this, you will not be able to see the
1834 events as you intended in the Event Log Viewer - it needs to be able to access
1835 the registry to get the .dll name. The current version does not do this (in fact
1836 it doesn't do anything).
1839 .. method:: NTEventLogHandler.emit(record)
1841 Determines the message ID, event category and event type, and then logs the
1842 message in the NT event log.
1845 .. method:: NTEventLogHandler.getEventCategory(record)
1847 Returns the event category for the record. Override this if you want to specify
1848 your own categories. This version returns 0.
1851 .. method:: NTEventLogHandler.getEventType(record)
1853 Returns the event type for the record. Override this if you want to specify your
1854 own types. This version does a mapping using the handler's typemap attribute,
1855 which is set up in :meth:`__init__` to a dictionary which contains mappings for
1856 :const:`DEBUG`, :const:`INFO`, :const:`WARNING`, :const:`ERROR` and
1857 :const:`CRITICAL`. If you are using your own levels, you will either need to
1858 override this method or place a suitable dictionary in the handler's *typemap*
1862 .. method:: NTEventLogHandler.getMessageID(record)
1864 Returns the message ID for the record. If you are using your own messages, you
1865 could do this by having the *msg* passed to the logger being an ID rather than a
1866 format string. Then, in here, you could use a dictionary lookup to get the
1867 message ID. This version returns 1, which is the base message ID in
1868 :file:`win32service.pyd`.
1874 The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1875 supports sending logging messages to an email address via SMTP.
1878 .. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1880 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1881 initialized with the from and to addresses and subject line of the email. The
1882 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1883 the (host, port) tuple format for the *mailhost* argument. If you use a string,
1884 the standard SMTP port is used. If your SMTP server requires authentication, you
1885 can specify a (username, password) tuple for the *credentials* argument.
1887 .. versionchanged:: 2.6
1888 *credentials* was added.
1891 .. method:: SMTPHandler.emit(record)
1893 Formats the record and sends it to the specified addressees.
1896 .. method:: SMTPHandler.getSubject(record)
1898 If you want to specify a subject line which is record-dependent, override this
1905 The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
1906 supports buffering of logging records in memory, periodically flushing them to a
1907 :dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
1908 event of a certain severity or greater is seen.
1910 :class:`MemoryHandler` is a subclass of the more general
1911 :class:`BufferingHandler`, which is an abstract class. This buffers logging
1912 records in memory. Whenever each record is added to the buffer, a check is made
1913 by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
1914 should, then :meth:`flush` is expected to do the needful.
1917 .. class:: BufferingHandler(capacity)
1919 Initializes the handler with a buffer of the specified capacity.
1922 .. method:: BufferingHandler.emit(record)
1924 Appends the record to the buffer. If :meth:`shouldFlush` returns true, calls
1925 :meth:`flush` to process the buffer.
1928 .. method:: BufferingHandler.flush()
1930 You can override this to implement custom flushing behavior. This version just
1931 zaps the buffer to empty.
1934 .. method:: BufferingHandler.shouldFlush(record)
1936 Returns true if the buffer is up to capacity. This method can be overridden to
1937 implement custom flushing strategies.
1940 .. class:: MemoryHandler(capacity[, flushLevel [, target]])
1942 Returns a new instance of the :class:`MemoryHandler` class. The instance is
1943 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
1944 :const:`ERROR` is used. If no *target* is specified, the target will need to be
1945 set using :meth:`setTarget` before this handler does anything useful.
1948 .. method:: MemoryHandler.close()
1950 Calls :meth:`flush`, sets the target to :const:`None` and clears the buffer.
1953 .. method:: MemoryHandler.flush()
1955 For a :class:`MemoryHandler`, flushing means just sending the buffered records
1956 to the target, if there is one. Override if you want different behavior.
1959 .. method:: MemoryHandler.setTarget(target)
1961 Sets the target handler for this handler.
1964 .. method:: MemoryHandler.shouldFlush(record)
1966 Checks for buffer full or a record at the *flushLevel* or higher.
1972 The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
1973 supports sending logging messages to a Web server, using either ``GET`` or
1977 .. class:: HTTPHandler(host, url[, method])
1979 Returns a new instance of the :class:`HTTPHandler` class. The instance is
1980 initialized with a host address, url and HTTP method. The *host* can be of the
1981 form ``host:port``, should you need to use a specific port number. If no
1982 *method* is specified, ``GET`` is used.
1985 .. method:: HTTPHandler.emit(record)
1987 Sends the record to the Web server as an URL-encoded dictionary.
1990 .. _formatter-objects:
1995 :class:`Formatter`\ s have the following attributes and methods. They are
1996 responsible for converting a :class:`LogRecord` to (usually) a string which can
1997 be interpreted by either a human or an external system. The base
1998 :class:`Formatter` allows a formatting string to be specified. If none is
1999 supplied, the default value of ``'%(message)s'`` is used.
2001 A Formatter can be initialized with a format string which makes use of knowledge
2002 of the :class:`LogRecord` attributes - such as the default value mentioned above
2003 making use of the fact that the user's message and arguments are pre-formatted
2004 into a :class:`LogRecord`'s *message* attribute. This format string contains
2005 standard python %-style mapping keys. See section :ref:`string-formatting`
2006 for more information on string formatting.
2008 Currently, the useful mapping keys in a :class:`LogRecord` are:
2010 +-------------------------+-----------------------------------------------+
2011 | Format | Description |
2012 +=========================+===============================================+
2013 | ``%(name)s`` | Name of the logger (logging channel). |
2014 +-------------------------+-----------------------------------------------+
2015 | ``%(levelno)s`` | Numeric logging level for the message |
2016 | | (:const:`DEBUG`, :const:`INFO`, |
2017 | | :const:`WARNING`, :const:`ERROR`, |
2018 | | :const:`CRITICAL`). |
2019 +-------------------------+-----------------------------------------------+
2020 | ``%(levelname)s`` | Text logging level for the message |
2021 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
2022 | | ``'ERROR'``, ``'CRITICAL'``). |
2023 +-------------------------+-----------------------------------------------+
2024 | ``%(pathname)s`` | Full pathname of the source file where the |
2025 | | logging call was issued (if available). |
2026 +-------------------------+-----------------------------------------------+
2027 | ``%(filename)s`` | Filename portion of pathname. |
2028 +-------------------------+-----------------------------------------------+
2029 | ``%(module)s`` | Module (name portion of filename). |
2030 +-------------------------+-----------------------------------------------+
2031 | ``%(funcName)s`` | Name of function containing the logging call. |
2032 +-------------------------+-----------------------------------------------+
2033 | ``%(lineno)d`` | Source line number where the logging call was |
2034 | | issued (if available). |
2035 +-------------------------+-----------------------------------------------+
2036 | ``%(created)f`` | Time when the :class:`LogRecord` was created |
2037 | | (as returned by :func:`time.time`). |
2038 +-------------------------+-----------------------------------------------+
2039 | ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
2040 | | created, relative to the time the logging |
2041 | | module was loaded. |
2042 +-------------------------+-----------------------------------------------+
2043 | ``%(asctime)s`` | Human-readable time when the |
2044 | | :class:`LogRecord` was created. By default |
2045 | | this is of the form "2003-07-08 16:49:45,896" |
2046 | | (the numbers after the comma are millisecond |
2047 | | portion of the time). |
2048 +-------------------------+-----------------------------------------------+
2049 | ``%(msecs)d`` | Millisecond portion of the time when the |
2050 | | :class:`LogRecord` was created. |
2051 +-------------------------+-----------------------------------------------+
2052 | ``%(thread)d`` | Thread ID (if available). |
2053 +-------------------------+-----------------------------------------------+
2054 | ``%(threadName)s`` | Thread name (if available). |
2055 +-------------------------+-----------------------------------------------+
2056 | ``%(process)d`` | Process ID (if available). |
2057 +-------------------------+-----------------------------------------------+
2058 | ``%(message)s`` | The logged message, computed as ``msg % |
2060 +-------------------------+-----------------------------------------------+
2062 .. versionchanged:: 2.5
2063 *funcName* was added.
2066 .. class:: Formatter([fmt[, datefmt]])
2068 Returns a new instance of the :class:`Formatter` class. The instance is
2069 initialized with a format string for the message as a whole, as well as a format
2070 string for the date/time portion of a message. If no *fmt* is specified,
2071 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
2075 .. method:: Formatter.format(record)
2077 The record's attribute dictionary is used as the operand to a string formatting
2078 operation. Returns the resulting string. Before formatting the dictionary, a
2079 couple of preparatory steps are carried out. The *message* attribute of the
2080 record is computed using *msg* % *args*. If the formatting string contains
2081 ``'(asctime)'``, :meth:`formatTime` is called to format the event time. If there
2082 is exception information, it is formatted using :meth:`formatException` and
2083 appended to the message.
2086 .. method:: Formatter.formatTime(record[, datefmt])
2088 This method should be called from :meth:`format` by a formatter which wants to
2089 make use of a formatted time. This method can be overridden in formatters to
2090 provide for any specific requirement, but the basic behavior is as follows: if
2091 *datefmt* (a string) is specified, it is used with :func:`time.strftime` to
2092 format the creation time of the record. Otherwise, the ISO8601 format is used.
2093 The resulting string is returned.
2096 .. method:: Formatter.formatException(exc_info)
2098 Formats the specified exception information (a standard exception tuple as
2099 returned by :func:`sys.exc_info`) as a string. This default implementation just
2100 uses :func:`traceback.print_exception`. The resulting string is returned.
2106 :class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
2107 more sophisticated filtering than is provided by levels. The base filter class
2108 only allows events which are below a certain point in the logger hierarchy. For
2109 example, a filter initialized with "A.B" will allow events logged by loggers
2110 "A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
2111 initialized with the empty string, all events are passed.
2114 .. class:: Filter([name])
2116 Returns an instance of the :class:`Filter` class. If *name* is specified, it
2117 names a logger which, together with its children, will have its events allowed
2118 through the filter. If no name is specified, allows every event.
2121 .. method:: Filter.filter(record)
2123 Is the specified record to be logged? Returns zero for no, nonzero for yes. If
2124 deemed appropriate, the record may be modified in-place by this method.
2130 :class:`LogRecord` instances are created every time something is logged. They
2131 contain all the information pertinent to the event being logged. The main
2132 information passed in is in msg and args, which are combined using msg % args to
2133 create the message field of the record. The record also includes information
2134 such as when the record was created, the source line where the logging call was
2135 made, and any exception information to be logged.
2138 .. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2140 Returns an instance of :class:`LogRecord` initialized with interesting
2141 information. The *name* is the logger name; *lvl* is the numeric level;
2142 *pathname* is the absolute pathname of the source file in which the logging
2143 call was made; *lineno* is the line number in that file where the logging
2144 call is found; *msg* is the user-supplied message (a format string); *args*
2145 is the tuple which, together with *msg*, makes up the user message; and
2146 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2147 (or :const:`None`, if no exception information is available). The *func* is
2148 the name of the function from which the logging call was made. If not
2149 specified, it defaults to ``None``.
2151 .. versionchanged:: 2.5
2155 .. method:: LogRecord.getMessage()
2157 Returns the message for this :class:`LogRecord` instance after merging any
2158 user-supplied arguments with the message.
2160 LoggerAdapter Objects
2161 ---------------------
2163 .. versionadded:: 2.6
2165 :class:`LoggerAdapter` instances are used to conveniently pass contextual
2166 information into logging calls. For a usage example , see context-info_.
2168 .. class:: LoggerAdapter(logger, extra)
2170 Returns an instance of :class:`LoggerAdapter` initialized with an
2171 underlying :class:`Logger` instance and a dict-like object.
2173 .. method:: LoggerAdapter.process(msg, kwargs)
2175 Modifies the message and/or keyword arguments passed to a logging call in
2176 order to insert contextual information. This implementation takes the
2177 object passed as *extra* to the constructor and adds it to *kwargs* using
2178 key 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
2179 (possibly modified) versions of the arguments passed in.
2181 In addition to the above, :class:`LoggerAdapter` supports all the logging
2182 methods of :class:`Logger`, i.e. :meth:`debug`, :meth:`info`, :meth:`warning`,
2183 :meth:`error`, :meth:`exception`, :meth:`critical` and :meth:`log`. These
2184 methods have the same signatures as their counterparts in :class:`Logger`, so
2185 you can use the two types of instances interchangeably.
2191 The logging module is intended to be thread-safe without any special work
2192 needing to be done by its clients. It achieves this though using threading
2193 locks; there is one lock to serialize access to the module's shared data, and
2194 each handler also creates a lock to serialize access to its underlying I/O.
2201 .. _logging-config-api:
2203 Configuration functions
2204 ^^^^^^^^^^^^^^^^^^^^^^^
2206 The following functions configure the logging module. They are located in the
2207 :mod:`logging.config` module. Their use is optional --- you can configure the
2208 logging module using these functions or by making calls to the main API (defined
2209 in :mod:`logging` itself) and defining handlers which are declared either in
2210 :mod:`logging` or :mod:`logging.handlers`.
2213 .. function:: fileConfig(fname[, defaults])
2215 Reads the logging configuration from a ConfigParser-format file named *fname*.
2216 This function can be called several times from an application, allowing an end
2217 user the ability to select from various pre-canned configurations (if the
2218 developer provides a mechanism to present the choices and load the chosen
2219 configuration). Defaults to be passed to ConfigParser can be specified in the
2220 *defaults* argument.
2223 .. function:: listen([port])
2225 Starts up a socket server on the specified port, and listens for new
2226 configurations. If no port is specified, the module's default
2227 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2228 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2229 :class:`Thread` instance on which you can call :meth:`start` to start the
2230 server, and which you can :meth:`join` when appropriate. To stop the server,
2231 call :func:`stopListening`.
2233 To send a configuration to the socket, read in the configuration file and
2234 send it to the socket as a string of bytes preceded by a four-byte length
2235 string packed in binary using ``struct.pack('>L', n)``.
2238 .. function:: stopListening()
2240 Stops the listening server which was created with a call to :func:`listen`.
2241 This is typically called before calling :meth:`join` on the return value from
2245 .. _logging-config-fileformat:
2247 Configuration file format
2248 ^^^^^^^^^^^^^^^^^^^^^^^^^
2250 The configuration file format understood by :func:`fileConfig` is based on
2251 ConfigParser functionality. The file must contain sections called ``[loggers]``,
2252 ``[handlers]`` and ``[formatters]`` which identify by name the entities of each
2253 type which are defined in the file. For each such entity, there is a separate
2254 section which identified how that entity is configured. Thus, for a logger named
2255 ``log01`` in the ``[loggers]`` section, the relevant configuration details are
2256 held in a section ``[logger_log01]``. Similarly, a handler called ``hand01`` in
2257 the ``[handlers]`` section will have its configuration held in a section called
2258 ``[handler_hand01]``, while a formatter called ``form01`` in the
2259 ``[formatters]`` section will have its configuration specified in a section
2260 called ``[formatter_form01]``. The root logger configuration must be specified
2261 in a section called ``[logger_root]``.
2263 Examples of these sections in the file are given below. ::
2266 keys=root,log02,log03,log04,log05,log06,log07
2269 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2272 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2274 The root logger must specify a level and a list of handlers. An example of a
2275 root logger section is given below. ::
2281 The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2282 ``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2283 logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2284 package's namespace.
2286 The ``handlers`` entry is a comma-separated list of handler names, which must
2287 appear in the ``[handlers]`` section. These names must appear in the
2288 ``[handlers]`` section and have corresponding sections in the configuration
2291 For loggers other than the root logger, some additional information is required.
2292 This is illustrated by the following example. ::
2298 qualname=compiler.parser
2300 The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2301 except that if a non-root logger's level is specified as ``NOTSET``, the system
2302 consults loggers higher up the hierarchy to determine the effective level of the
2303 logger. The ``propagate`` entry is set to 1 to indicate that messages must
2304 propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2305 indicate that messages are **not** propagated to handlers up the hierarchy. The
2306 ``qualname`` entry is the hierarchical channel name of the logger, that is to
2307 say the name used by the application to get the logger.
2309 Sections which specify handler configuration are exemplified by the following.
2318 The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2319 in the ``logging`` package's namespace). The ``level`` is interpreted as for
2320 loggers, and ``NOTSET`` is taken to mean "log everything".
2322 The ``formatter`` entry indicates the key name of the formatter for this
2323 handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2324 If a name is specified, it must appear in the ``[formatters]`` section and have
2325 a corresponding section in the configuration file.
2327 The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2328 package's namespace, is the list of arguments to the constructor for the handler
2329 class. Refer to the constructors for the relevant handlers, or to the examples
2330 below, to see how typical entries are constructed. ::
2336 args=('python.log', 'w')
2339 class=handlers.SocketHandler
2342 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2345 class=handlers.DatagramHandler
2348 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2351 class=handlers.SysLogHandler
2354 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2357 class=handlers.NTEventLogHandler
2360 args=('Python Application', '', 'Application')
2363 class=handlers.SMTPHandler
2366 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2369 class=handlers.MemoryHandler
2376 class=handlers.HTTPHandler
2379 args=('localhost:9022', '/log', 'GET')
2381 Sections which specify formatter configuration are typified by the following. ::
2384 format=F1 %(asctime)s %(levelname)s %(message)s
2386 class=logging.Formatter
2388 The ``format`` entry is the overall format string, and the ``datefmt`` entry is
2389 the :func:`strftime`\ -compatible date/time format string. If empty, the
2390 package substitutes ISO8601 format date/times, which is almost equivalent to
2391 specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2392 also specifies milliseconds, which are appended to the result of using the above
2393 format string, with a comma separator. An example time in ISO8601 format is
2394 ``2003-01-23 00:29:50,411``.
2396 The ``class`` entry is optional. It indicates the name of the formatter's class
2397 (as a dotted module and class name.) This option is useful for instantiating a
2398 :class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2399 exception tracebacks in an expanded or condensed format.
2402 Configuration server example
2403 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2405 Here is an example of a module using the logging configuration server::
2408 import logging.config
2412 # read initial config file
2413 logging.config.fileConfig("logging.conf")
2415 # create and start listener on port 9999
2416 t = logging.config.listen(9999)
2419 logger = logging.getLogger("simpleExample")
2422 # loop through logging calls to see the difference
2423 # new configurations make, until Ctrl+C is pressed
2425 logger.debug("debug message")
2426 logger.info("info message")
2427 logger.warn("warn message")
2428 logger.error("error message")
2429 logger.critical("critical message")
2431 except KeyboardInterrupt:
2433 logging.config.stopListening()
2436 And here is a script that takes a filename and sends that file to the server,
2437 properly preceded with the binary-encoded length, as the new logging
2440 #!/usr/bin/env python
2441 import socket, sys, struct
2443 data_to_send = open(sys.argv[1], "r").read()
2447 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2448 print "connecting..."
2449 s.connect((HOST, PORT))
2450 print "sending config..."
2451 s.send(struct.pack(">L", len(data_to_send)))
2452 s.send(data_to_send)
2460 Multiple handlers and formatters
2461 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2463 Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2464 or maximum quota for the number of handlers you may add. Sometimes it will be
2465 beneficial for an application to log all messages of all severities to a text
2466 file while simultaneously logging errors or above to the console. To set this
2467 up, simply configure the appropriate handlers. The logging calls in the
2468 application code will remain unchanged. Here is a slight modification to the
2469 previous simple module-based configuration example::
2473 logger = logging.getLogger("simple_example")
2474 logger.setLevel(logging.DEBUG)
2475 # create file handler which logs even debug messages
2476 fh = logging.FileHandler("spam.log")
2477 fh.setLevel(logging.DEBUG)
2478 # create console handler with a higher log level
2479 ch = logging.StreamHandler()
2480 ch.setLevel(logging.ERROR)
2481 # create formatter and add it to the handlers
2482 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2483 ch.setFormatter(formatter)
2484 fh.setFormatter(formatter)
2485 # add the handlers to logger
2486 logger.addHandler(ch)
2487 logger.addHandler(fh)
2489 # "application" code
2490 logger.debug("debug message")
2491 logger.info("info message")
2492 logger.warn("warn message")
2493 logger.error("error message")
2494 logger.critical("critical message")
2496 Notice that the "application" code does not care about multiple handlers. All
2497 that changed was the addition and configuration of a new handler named *fh*.
2499 The ability to create new handlers with higher- or lower-severity filters can be
2500 very helpful when writing and testing an application. Instead of using many
2501 ``print`` statements for debugging, use ``logger.debug``: Unlike the print
2502 statements, which you will have to delete or comment out later, the logger.debug
2503 statements can remain intact in the source code and remain dormant until you
2504 need them again. At that time, the only change that needs to happen is to
2505 modify the severity level of the logger and/or handler to debug.
2508 Using logging in multiple modules
2509 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2511 It was mentioned above that multiple calls to
2512 ``logging.getLogger('someLogger')`` return a reference to the same logger
2513 object. This is true not only within the same module, but also across modules
2514 as long as it is in the same Python interpreter process. It is true for
2515 references to the same object; additionally, application code can define and
2516 configure a parent logger in one module and create (but not configure) a child
2517 logger in a separate module, and all logger calls to the child will pass up to
2518 the parent. Here is a main module::
2521 import auxiliary_module
2523 # create logger with "spam_application"
2524 logger = logging.getLogger("spam_application")
2525 logger.setLevel(logging.DEBUG)
2526 # create file handler which logs even debug messages
2527 fh = logging.FileHandler("spam.log")
2528 fh.setLevel(logging.DEBUG)
2529 # create console handler with a higher log level
2530 ch = logging.StreamHandler()
2531 ch.setLevel(logging.ERROR)
2532 # create formatter and add it to the handlers
2533 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2534 fh.setFormatter(formatter)
2535 ch.setFormatter(formatter)
2536 # add the handlers to the logger
2537 logger.addHandler(fh)
2538 logger.addHandler(ch)
2540 logger.info("creating an instance of auxiliary_module.Auxiliary")
2541 a = auxiliary_module.Auxiliary()
2542 logger.info("created an instance of auxiliary_module.Auxiliary")
2543 logger.info("calling auxiliary_module.Auxiliary.do_something")
2545 logger.info("finished auxiliary_module.Auxiliary.do_something")
2546 logger.info("calling auxiliary_module.some_function()")
2547 auxiliary_module.some_function()
2548 logger.info("done with auxiliary_module.some_function()")
2550 Here is the auxiliary module::
2555 module_logger = logging.getLogger("spam_application.auxiliary")
2559 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2560 self.logger.info("creating an instance of Auxiliary")
2561 def do_something(self):
2562 self.logger.info("doing something")
2564 self.logger.info("done doing something")
2566 def some_function():
2567 module_logger.info("received a call to \"some_function\"")
2569 The output looks like this::
2571 2005-03-23 23:47:11,663 - spam_application - INFO -
2572 creating an instance of auxiliary_module.Auxiliary
2573 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
2574 creating an instance of Auxiliary
2575 2005-03-23 23:47:11,665 - spam_application - INFO -
2576 created an instance of auxiliary_module.Auxiliary
2577 2005-03-23 23:47:11,668 - spam_application - INFO -
2578 calling auxiliary_module.Auxiliary.do_something
2579 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
2581 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
2582 done doing something
2583 2005-03-23 23:47:11,670 - spam_application - INFO -
2584 finished auxiliary_module.Auxiliary.do_something
2585 2005-03-23 23:47:11,671 - spam_application - INFO -
2586 calling auxiliary_module.some_function()
2587 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
2588 received a call to "some_function"
2589 2005-03-23 23:47:11,673 - spam_application - INFO -
2590 done with auxiliary_module.some_function()