1 :mod:`logging` --- Logging facility for Python
2 ==============================================
5 :synopsis: Flexible error logging system for applications.
8 .. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
9 .. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
12 .. index:: pair: Errors; logging
16 This module defines functions and classes which implement a flexible error
17 logging system for applications.
19 Logging is performed by calling methods on instances of the :class:`Logger`
20 class (hereafter called :dfn:`loggers`). Each instance has a name, and they are
21 conceptually arranged in a namespace hierarchy using dots (periods) as
22 separators. For example, a logger named "scan" is the parent of loggers
23 "scan.text", "scan.html" and "scan.pdf". Logger names can be anything you want,
24 and indicate the area of an application in which a logged message originates.
26 Logged messages also have levels of importance associated with them. The default
27 levels provided are :const:`DEBUG`, :const:`INFO`, :const:`WARNING`,
28 :const:`ERROR` and :const:`CRITICAL`. As a convenience, you indicate the
29 importance of a logged message by calling an appropriate method of
30 :class:`Logger`. The methods are :meth:`debug`, :meth:`info`, :meth:`warning`,
31 :meth:`error` and :meth:`critical`, which mirror the default levels. You are not
32 constrained to use these levels: you can specify your own and use a more general
33 :class:`Logger` method, :meth:`log`, which takes an explicit level argument.
39 The key benefit of having the logging API provided by a standard library module
40 is that all Python modules can participate in logging, so your application log
41 can include messages from third-party modules.
43 It is, of course, possible to log messages with different verbosity levels or to
44 different destinations. Support for writing log messages to files, HTTP
45 GET/POST locations, email via SMTP, generic sockets, or OS-specific logging
46 mechanisms are all supported by the standard module. You can also create your
47 own log destination class if you have special requirements not met by any of the
53 .. sectionauthor:: Doug Hellmann
54 .. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>)
56 Most applications are probably going to want to log to a file, so let's start
57 with that case. Using the :func:`basicConfig` function, we can set up the
58 default handler so that debug messages are written to a file::
61 LOG_FILENAME = '/tmp/logging_example.out'
62 logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,)
64 logging.debug('This message should go to the log file')
66 And now if we open the file and look at what we have, we should find the log
69 DEBUG:root:This message should go to the log file
71 If you run the script repeatedly, the additional log messages are appended to
72 the file. To create a new file each time, you can pass a filemode argument to
73 :func:`basicConfig` with a value of ``'w'``. Rather than managing the file size
74 yourself, though, it is simpler to use a :class:`RotatingFileHandler`::
78 import logging.handlers
80 LOG_FILENAME = '/tmp/logging_rotatingfile_example.out'
82 # Set up a specific logger with our desired output level
83 my_logger = logging.getLogger('MyLogger')
84 my_logger.setLevel(logging.DEBUG)
86 # Add the log message handler to the logger
87 handler = logging.handlers.RotatingFileHandler(
88 LOG_FILENAME, maxBytes=20, backupCount=5)
90 my_logger.addHandler(handler)
94 my_logger.debug('i = %d' % i)
96 # See what files are created
97 logfiles = glob.glob('%s*' % LOG_FILENAME)
99 for filename in logfiles:
102 The result should be 6 separate files, each with part of the log history for the
105 /tmp/logging_rotatingfile_example.out
106 /tmp/logging_rotatingfile_example.out.1
107 /tmp/logging_rotatingfile_example.out.2
108 /tmp/logging_rotatingfile_example.out.3
109 /tmp/logging_rotatingfile_example.out.4
110 /tmp/logging_rotatingfile_example.out.5
112 The most current file is always :file:`/tmp/logging_rotatingfile_example.out`,
113 and each time it reaches the size limit it is renamed with the suffix
114 ``.1``. Each of the existing backup files is renamed to increment the suffix
115 (``.1`` becomes ``.2``, etc.) and the ``.5`` file is erased.
117 Obviously this example sets the log length much much too small as an extreme
118 example. You would want to set *maxBytes* to an appropriate value.
120 Another useful feature of the logging API is the ability to produce different
121 messages at different log levels. This allows you to instrument your code with
122 debug messages, for example, but turning the log level down so that those debug
123 messages are not written for your production system. The default levels are
124 ``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO``, ``DEBUG`` and ``NOTSET``.
126 The logger, handler, and log message call each specify a level. The log message
127 is only emitted if the handler and logger are configured to emit messages of
128 that level or lower. For example, if a message is ``CRITICAL``, and the logger
129 is set to ``ERROR``, the message is emitted. If a message is a ``WARNING``, and
130 the logger is set to produce only ``ERROR``\s, the message is not emitted::
135 LEVELS = {'debug': logging.DEBUG,
136 'info': logging.INFO,
137 'warning': logging.WARNING,
138 'error': logging.ERROR,
139 'critical': logging.CRITICAL}
141 if len(sys.argv) > 1:
142 level_name = sys.argv[1]
143 level = LEVELS.get(level_name, logging.NOTSET)
144 logging.basicConfig(level=level)
146 logging.debug('This is a debug message')
147 logging.info('This is an info message')
148 logging.warning('This is a warning message')
149 logging.error('This is an error message')
150 logging.critical('This is a critical error message')
152 Run the script with an argument like 'debug' or 'warning' to see which messages
153 show up at different levels::
155 $ python logging_level_example.py debug
156 DEBUG:root:This is a debug message
157 INFO:root:This is an info message
158 WARNING:root:This is a warning message
159 ERROR:root:This is an error message
160 CRITICAL:root:This is a critical error message
162 $ python logging_level_example.py info
163 INFO:root:This is an info message
164 WARNING:root:This is a warning message
165 ERROR:root:This is an error message
166 CRITICAL:root:This is a critical error message
168 You will notice that these log messages all have ``root`` embedded in them. The
169 logging module supports a hierarchy of loggers with different names. An easy
170 way to tell where a specific log message comes from is to use a separate logger
171 object for each of your modules. Each new logger "inherits" the configuration
172 of its parent, and log messages sent to a logger include the name of that
173 logger. Optionally, each logger can be configured differently, so that messages
174 from different modules are handled in different ways. Let's look at a simple
175 example of how to log from different modules so it is easy to trace the source
180 logging.basicConfig(level=logging.WARNING)
182 logger1 = logging.getLogger('package1.module1')
183 logger2 = logging.getLogger('package2.module2')
185 logger1.warning('This message comes from one module')
186 logger2.warning('And this message comes from another module')
190 $ python logging_modules_example.py
191 WARNING:package1.module1:This message comes from one module
192 WARNING:package2.module2:And this message comes from another module
194 There are many more options for configuring logging, including different log
195 message formatting options, having messages delivered to multiple destinations,
196 and changing the configuration of a long-running application on the fly using a
197 socket interface. All of these options are covered in depth in the library
198 module documentation.
203 The logging library takes a modular approach and offers the several categories
204 of components: loggers, handlers, filters, and formatters. Loggers expose the
205 interface that application code directly uses. Handlers send the log records to
206 the appropriate destination. Filters provide a finer grained facility for
207 determining which log records to send on to a handler. Formatters specify the
208 layout of the resultant log record.
210 :class:`Logger` objects have a threefold job. First, they expose several
211 methods to application code so that applications can log messages at runtime.
212 Second, logger objects determine which log messages to act upon based upon
213 severity (the default filtering facility) or filter objects. Third, logger
214 objects pass along relevant log messages to all interested log handlers.
216 The most widely used methods on logger objects fall into two categories:
217 configuration and message sending.
219 * :meth:`Logger.setLevel` specifies the lowest-severity log message a logger
220 will handle, where debug is the lowest built-in severity level and critical is
221 the highest built-in severity. For example, if the severity level is info,
222 the logger will handle only info, warning, error, and critical messages and
223 will ignore debug messages.
225 * :meth:`Logger.addFilter` and :meth:`Logger.removeFilter` add and remove filter
226 objects from the logger object. This tutorial does not address filters.
228 With the logger object configured, the following methods create log messages:
230 * :meth:`Logger.debug`, :meth:`Logger.info`, :meth:`Logger.warning`,
231 :meth:`Logger.error`, and :meth:`Logger.critical` all create log records with
232 a message and a level that corresponds to their respective method names. The
233 message is actually a format string, which may contain the standard string
234 substitution syntax of :const:`%s`, :const:`%d`, :const:`%f`, and so on. The
235 rest of their arguments is a list of objects that correspond with the
236 substitution fields in the message. With regard to :const:`**kwargs`, the
237 logging methods care only about a keyword of :const:`exc_info` and use it to
238 determine whether to log exception information.
240 * :meth:`Logger.exception` creates a log message similar to
241 :meth:`Logger.error`. The difference is that :meth:`Logger.exception` dumps a
242 stack trace along with it. Call this method only from an exception handler.
244 * :meth:`Logger.log` takes a log level as an explicit argument. This is a
245 little more verbose for logging messages than using the log level convenience
246 methods listed above, but this is how to log at custom log levels.
248 :func:`getLogger` returns a reference to a logger instance with the specified
249 if it it is provided, or ``root`` if not. The names are period-separated
250 hierarchical structures. Multiple calls to :func:`getLogger` with the same name
251 will return a reference to the same logger object. Loggers that are further
252 down in the hierarchical list are children of loggers higher up in the list.
253 For example, given a logger with a name of ``foo``, loggers with names of
254 ``foo.bar``, ``foo.bar.baz``, and ``foo.bam`` are all children of ``foo``.
255 Child loggers propagate messages up to their parent loggers. Because of this,
256 it is unnecessary to define and configure all the loggers an application uses.
257 It is sufficient to configure a top-level logger and create child loggers as
264 :class:`Handler` objects are responsible for dispatching the appropriate log
265 messages (based on the log messages' severity) to the handler's specified
266 destination. Logger objects can add zero or more handler objects to themselves
267 with an :func:`addHandler` method. As an example scenario, an application may
268 want to send all log messages to a log file, all log messages of error or higher
269 to stdout, and all messages of critical to an email address. This scenario
270 requires three individual handlers where each handler is responsible for sending
271 messages of a specific severity to a specific location.
273 The standard library includes quite a few handler types; this tutorial uses only
274 :class:`StreamHandler` and :class:`FileHandler` in its examples.
276 There are very few methods in a handler for application developers to concern
277 themselves with. The only handler methods that seem relevant for application
278 developers who are using the built-in handler objects (that is, not creating
279 custom handlers) are the following configuration methods:
281 * The :meth:`Handler.setLevel` method, just as in logger objects, specifies the
282 lowest severity that will be dispatched to the appropriate destination. Why
283 are there two :func:`setLevel` methods? The level set in the logger
284 determines which severity of messages it will pass to its handlers. The level
285 set in each handler determines which messages that handler will send on.
286 :func:`setFormatter` selects a Formatter object for this handler to use.
288 * :func:`addFilter` and :func:`removeFilter` respectively configure and
289 deconfigure filter objects on handlers.
291 Application code should not directly instantiate and use handlers. Instead, the
292 :class:`Handler` class is a base class that defines the interface that all
293 Handlers should have and establishes some default behavior that child classes
294 can use (or override).
300 Formatter objects configure the final order, structure, and contents of the log
301 message. Unlike the base :class:`logging.Handler` class, application code may
302 instantiate formatter classes, although you could likely subclass the formatter
303 if your application needs special behavior. The constructor takes two optional
304 arguments: a message format string and a date format string. If there is no
305 message format string, the default is to use the raw message. If there is no
306 date format string, the default date format is::
310 with the milliseconds tacked on at the end.
312 The message format string uses ``%(<dictionary key>)s`` styled string
313 substitution; the possible keys are documented in :ref:`formatter-objects`.
315 The following message format string will log the time in a human-readable
316 format, the severity of the message, and the contents of the message, in that
319 "%(asctime)s - %(levelname)s - %(message)s"
325 Programmers can configure logging either by creating loggers, handlers, and
326 formatters explicitly in a main module with the configuration methods listed
327 above (using Python code), or by creating a logging config file. The following
328 code is an example of configuring a very simple logger, a console handler, and a
329 simple formatter in a Python module::
334 logger = logging.getLogger("simple_example")
335 logger.setLevel(logging.DEBUG)
336 # create console handler and set level to debug
337 ch = logging.StreamHandler()
338 ch.setLevel(logging.DEBUG)
340 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
341 # add formatter to ch
342 ch.setFormatter(formatter)
344 logger.addHandler(ch)
347 logger.debug("debug message")
348 logger.info("info message")
349 logger.warn("warn message")
350 logger.error("error message")
351 logger.critical("critical message")
353 Running this module from the command line produces the following output::
355 $ python simple_logging_module.py
356 2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message
357 2005-03-19 15:10:26,620 - simple_example - INFO - info message
358 2005-03-19 15:10:26,695 - simple_example - WARNING - warn message
359 2005-03-19 15:10:26,697 - simple_example - ERROR - error message
360 2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message
362 The following Python module creates a logger, handler, and formatter nearly
363 identical to those in the example listed above, with the only difference being
364 the names of the objects::
367 import logging.config
369 logging.config.fileConfig("logging.conf")
372 logger = logging.getLogger("simpleExample")
375 logger.debug("debug message")
376 logger.info("info message")
377 logger.warn("warn message")
378 logger.error("error message")
379 logger.critical("critical message")
381 Here is the logging.conf file::
384 keys=root,simpleExample
394 handlers=consoleHandler
396 [logger_simpleExample]
398 handlers=consoleHandler
399 qualname=simpleExample
402 [handler_consoleHandler]
405 formatter=simpleFormatter
408 [formatter_simpleFormatter]
409 format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
412 The output is nearly identical to that of the non-config-file-based example::
414 $ python simple_logging_config.py
415 2005-03-19 15:38:55,977 - simpleExample - DEBUG - debug message
416 2005-03-19 15:38:55,979 - simpleExample - INFO - info message
417 2005-03-19 15:38:56,054 - simpleExample - WARNING - warn message
418 2005-03-19 15:38:56,055 - simpleExample - ERROR - error message
419 2005-03-19 15:38:56,130 - simpleExample - CRITICAL - critical message
421 You can see that the config file approach has a few advantages over the Python
422 code approach, mainly separation of configuration and code and the ability of
423 noncoders to easily modify the logging properties.
427 Configuring Logging for a Library
428 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
430 When developing a library which uses logging, some consideration needs to be
431 given to its configuration. If the using application does not use logging, and
432 library code makes logging calls, then a one-off message "No handlers could be
433 found for logger X.Y.Z" is printed to the console. This message is intended
434 to catch mistakes in logging configuration, but will confuse an application
435 developer who is not aware of logging by the library.
437 In addition to documenting how a library uses logging, a good way to configure
438 library logging so that it does not cause a spurious message is to add a
439 handler which does nothing. This avoids the message being printed, since a
440 handler will be found: it just doesn't produce any output. If the library user
441 configures logging for application use, presumably that configuration will add
442 some handlers, and if levels are suitably configured then logging calls made
443 in library code will send output to those handlers, as normal.
445 A do-nothing handler can be simply defined as follows::
449 class NullHandler(logging.Handler):
450 def emit(self, record):
453 An instance of this handler should be added to the top-level logger of the
454 logging namespace used by the library. If all logging by a library *foo* is
455 done using loggers with names matching "foo.x.y", then the code::
460 logging.getLogger("foo").addHandler(h)
462 should have the desired effect. If an organisation produces a number of
463 libraries, then the logger name specified can be "orgname.foo" rather than
466 .. versionadded:: 2.7
468 The :class:`NullHandler` class was not present in previous versions, but is now
469 included, so that it need not be defined in library code.
476 The numeric values of logging levels are given in the following table. These are
477 primarily of interest if you want to define your own levels, and need them to
478 have specific values relative to the predefined levels. If you define a level
479 with the same numeric value, it overwrites the predefined value; the predefined
482 +--------------+---------------+
483 | Level | Numeric value |
484 +==============+===============+
485 | ``CRITICAL`` | 50 |
486 +--------------+---------------+
488 +--------------+---------------+
490 +--------------+---------------+
492 +--------------+---------------+
494 +--------------+---------------+
496 +--------------+---------------+
498 Levels can also be associated with loggers, being set either by the developer or
499 through loading a saved logging configuration. When a logging method is called
500 on a logger, the logger compares its own level with the level associated with
501 the method call. If the logger's level is higher than the method call's, no
502 logging message is actually generated. This is the basic mechanism controlling
503 the verbosity of logging output.
505 Logging messages are encoded as instances of the :class:`LogRecord` class. When
506 a logger decides to actually log an event, a :class:`LogRecord` instance is
507 created from the logging message.
509 Logging messages are subjected to a dispatch mechanism through the use of
510 :dfn:`handlers`, which are instances of subclasses of the :class:`Handler`
511 class. Handlers are responsible for ensuring that a logged message (in the form
512 of a :class:`LogRecord`) ends up in a particular location (or set of locations)
513 which is useful for the target audience for that message (such as end users,
514 support desk staff, system administrators, developers). Handlers are passed
515 :class:`LogRecord` instances intended for particular destinations. Each logger
516 can have zero, one or more handlers associated with it (via the
517 :meth:`addHandler` method of :class:`Logger`). In addition to any handlers
518 directly associated with a logger, *all handlers associated with all ancestors
519 of the logger* are called to dispatch the message.
521 Just as for loggers, handlers can have levels associated with them. A handler's
522 level acts as a filter in the same way as a logger's level does. If a handler
523 decides to actually dispatch an event, the :meth:`emit` method is used to send
524 the message to its destination. Most user-defined subclasses of :class:`Handler`
525 will need to override this :meth:`emit`.
530 In addition to the base :class:`Handler` class, many useful subclasses are
533 #. :class:`StreamHandler` instances send error messages to streams (file-like
536 #. :class:`FileHandler` instances send error messages to disk files.
538 .. module:: logging.handlers
540 #. :class:`BaseRotatingHandler` is the base class for handlers that
541 rotate log files at a certain point. It is not meant to be instantiated
542 directly. Instead, use :class:`RotatingFileHandler` or
543 :class:`TimedRotatingFileHandler`.
545 #. :class:`RotatingFileHandler` instances send error messages to disk
546 files, with support for maximum log file sizes and log file rotation.
548 #. :class:`TimedRotatingFileHandler` instances send error messages to
549 disk files, rotating the log file at certain timed intervals.
551 #. :class:`SocketHandler` instances send error messages to TCP/IP
554 #. :class:`DatagramHandler` instances send error messages to UDP
557 #. :class:`SMTPHandler` instances send error messages to a designated
560 #. :class:`SysLogHandler` instances send error messages to a Unix
561 syslog daemon, possibly on a remote machine.
563 #. :class:`NTEventLogHandler` instances send error messages to a
564 Windows NT/2000/XP event log.
566 #. :class:`MemoryHandler` instances send error messages to a buffer
567 in memory, which is flushed whenever specific criteria are met.
569 #. :class:`HTTPHandler` instances send error messages to an HTTP
570 server using either ``GET`` or ``POST`` semantics.
572 #. :class:`WatchedFileHandler` instances watch the file they are
573 logging to. If the file changes, it is closed and reopened using the file
574 name. This handler is only useful on Unix-like systems; Windows does not
575 support the underlying mechanism used.
577 .. currentmodule:: logging
579 #. :class:`NullHandler` instances do nothing with error messages. They are used
580 by library developers who want to use logging, but want to avoid the "No
581 handlers could be found for logger XXX" message which can be displayed if
582 the library user has not configured logging. See :ref:`library-config` for
585 .. versionadded:: 2.7
587 The :class:`NullHandler` class was not present in previous versions.
589 The :class:`NullHandler`, :class:`StreamHandler` and :class:`FileHandler`
590 classes are defined in the core logging package. The other handlers are
591 defined in a sub- module, :mod:`logging.handlers`. (There is also another
592 sub-module, :mod:`logging.config`, for configuration functionality.)
594 Logged messages are formatted for presentation through instances of the
595 :class:`Formatter` class. They are initialized with a format string suitable for
596 use with the % operator and a dictionary.
598 For formatting multiple messages in a batch, instances of
599 :class:`BufferingFormatter` can be used. In addition to the format string (which
600 is applied to each message in the batch), there is provision for header and
601 trailer format strings.
603 When filtering based on logger level and/or handler level is not enough,
604 instances of :class:`Filter` can be added to both :class:`Logger` and
605 :class:`Handler` instances (through their :meth:`addFilter` method). Before
606 deciding to process a message further, both loggers and handlers consult all
607 their filters for permission. If any filter returns a false value, the message
608 is not processed further.
610 The basic :class:`Filter` functionality allows filtering by specific logger
611 name. If this feature is used, messages sent to the named logger and its
612 children are allowed through the filter, and all others dropped.
614 Module-Level Functions
615 ----------------------
617 In addition to the classes described above, there are a number of module- level
621 .. function:: getLogger([name])
623 Return a logger with the specified name or, if no name is specified, return a
624 logger which is the root logger of the hierarchy. If specified, the name is
625 typically a dot-separated hierarchical name like *"a"*, *"a.b"* or *"a.b.c.d"*.
626 Choice of these names is entirely up to the developer who is using logging.
628 All calls to this function with a given name return the same logger instance.
629 This means that logger instances never need to be passed between different parts
633 .. function:: getLoggerClass()
635 Return either the standard :class:`Logger` class, or the last class passed to
636 :func:`setLoggerClass`. This function may be called from within a new class
637 definition, to ensure that installing a customised :class:`Logger` class will
638 not undo customisations already applied by other code. For example::
640 class MyLogger(logging.getLoggerClass()):
641 # ... override behaviour here
644 .. function:: debug(msg[, *args[, **kwargs]])
646 Logs a message with level :const:`DEBUG` on the root logger. The *msg* is the
647 message format string, and the *args* are the arguments which are merged into
648 *msg* using the string formatting operator. (Note that this means that you can
649 use keywords in the format string, together with a single dictionary argument.)
651 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
652 which, if it does not evaluate as false, causes exception information to be
653 added to the logging message. If an exception tuple (in the format returned by
654 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
655 is called to get the exception information.
657 The other optional keyword argument is *extra* which can be used to pass a
658 dictionary which is used to populate the __dict__ of the LogRecord created for
659 the logging event with user-defined attributes. These custom attributes can then
660 be used as you like. For example, they could be incorporated into logged
661 messages. For example::
663 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
664 logging.basicConfig(format=FORMAT)
665 d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
666 logging.warning("Protocol problem: %s", "connection reset", extra=d)
668 would print something like ::
670 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
672 The keys in the dictionary passed in *extra* should not clash with the keys used
673 by the logging system. (See the :class:`Formatter` documentation for more
674 information on which keys are used by the logging system.)
676 If you choose to use these attributes in logged messages, you need to exercise
677 some care. In the above example, for instance, the :class:`Formatter` has been
678 set up with a format string which expects 'clientip' and 'user' in the attribute
679 dictionary of the LogRecord. If these are missing, the message will not be
680 logged because a string formatting exception will occur. So in this case, you
681 always need to pass the *extra* dictionary with these keys.
683 While this might be annoying, this feature is intended for use in specialized
684 circumstances, such as multi-threaded servers where the same code executes in
685 many contexts, and interesting conditions which arise are dependent on this
686 context (such as remote client IP address and authenticated user name, in the
687 above example). In such circumstances, it is likely that specialized
688 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
690 .. versionchanged:: 2.5
694 .. function:: info(msg[, *args[, **kwargs]])
696 Logs a message with level :const:`INFO` on the root logger. The arguments are
697 interpreted as for :func:`debug`.
700 .. function:: warning(msg[, *args[, **kwargs]])
702 Logs a message with level :const:`WARNING` on the root logger. The arguments are
703 interpreted as for :func:`debug`.
706 .. function:: error(msg[, *args[, **kwargs]])
708 Logs a message with level :const:`ERROR` on the root logger. The arguments are
709 interpreted as for :func:`debug`.
712 .. function:: critical(msg[, *args[, **kwargs]])
714 Logs a message with level :const:`CRITICAL` on the root logger. The arguments
715 are interpreted as for :func:`debug`.
718 .. function:: exception(msg[, *args])
720 Logs a message with level :const:`ERROR` on the root logger. The arguments are
721 interpreted as for :func:`debug`. Exception info is added to the logging
722 message. This function should only be called from an exception handler.
725 .. function:: log(level, msg[, *args[, **kwargs]])
727 Logs a message with level *level* on the root logger. The other arguments are
728 interpreted as for :func:`debug`.
731 .. function:: disable(lvl)
733 Provides an overriding level *lvl* for all loggers which takes precedence over
734 the logger's own level. When the need arises to temporarily throttle logging
735 output down across the whole application, this function can be useful.
738 .. function:: addLevelName(lvl, levelName)
740 Associates level *lvl* with text *levelName* in an internal dictionary, which is
741 used to map numeric levels to a textual representation, for example when a
742 :class:`Formatter` formats a message. This function can also be used to define
743 your own levels. The only constraints are that all levels used must be
744 registered using this function, levels should be positive integers and they
745 should increase in increasing order of severity.
748 .. function:: getLevelName(lvl)
750 Returns the textual representation of logging level *lvl*. If the level is one
751 of the predefined levels :const:`CRITICAL`, :const:`ERROR`, :const:`WARNING`,
752 :const:`INFO` or :const:`DEBUG` then you get the corresponding string. If you
753 have associated levels with names using :func:`addLevelName` then the name you
754 have associated with *lvl* is returned. If a numeric value corresponding to one
755 of the defined levels is passed in, the corresponding string representation is
756 returned. Otherwise, the string "Level %s" % lvl is returned.
759 .. function:: makeLogRecord(attrdict)
761 Creates and returns a new :class:`LogRecord` instance whose attributes are
762 defined by *attrdict*. This function is useful for taking a pickled
763 :class:`LogRecord` attribute dictionary, sent over a socket, and reconstituting
764 it as a :class:`LogRecord` instance at the receiving end.
767 .. function:: basicConfig([**kwargs])
769 Does basic configuration for the logging system by creating a
770 :class:`StreamHandler` with a default :class:`Formatter` and adding it to the
771 root logger. The function does nothing if any handlers have been defined for
772 the root logger. The functions :func:`debug`, :func:`info`, :func:`warning`,
773 :func:`error` and :func:`critical` will call :func:`basicConfig` automatically
774 if no handlers are defined for the root logger.
776 This function does nothing if the root logger already has handlers configured.
778 .. versionchanged:: 2.4
779 Formerly, :func:`basicConfig` did not take any keyword arguments.
781 The following keyword arguments are supported.
783 +--------------+---------------------------------------------+
784 | Format | Description |
785 +==============+=============================================+
786 | ``filename`` | Specifies that a FileHandler be created, |
787 | | using the specified filename, rather than a |
789 +--------------+---------------------------------------------+
790 | ``filemode`` | Specifies the mode to open the file, if |
791 | | filename is specified (if filemode is |
792 | | unspecified, it defaults to 'a'). |
793 +--------------+---------------------------------------------+
794 | ``format`` | Use the specified format string for the |
796 +--------------+---------------------------------------------+
797 | ``datefmt`` | Use the specified date/time format. |
798 +--------------+---------------------------------------------+
799 | ``level`` | Set the root logger level to the specified |
801 +--------------+---------------------------------------------+
802 | ``stream`` | Use the specified stream to initialize the |
803 | | StreamHandler. Note that this argument is |
804 | | incompatible with 'filename' - if both are |
805 | | present, 'stream' is ignored. |
806 +--------------+---------------------------------------------+
809 .. function:: shutdown()
811 Informs the logging system to perform an orderly shutdown by flushing and
812 closing all handlers. This should be called at application exit and no
813 further use of the logging system should be made after this call.
816 .. function:: setLoggerClass(klass)
818 Tells the logging system to use the class *klass* when instantiating a logger.
819 The class should define :meth:`__init__` such that only a name argument is
820 required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
821 function is typically called before any loggers are instantiated by applications
822 which need to use custom logger behavior.
827 :pep:`282` - A Logging System
828 The proposal which described this feature for inclusion in the Python standard
831 `Original Python logging package <http://www.red-dove.com/python_logging.html>`_
832 This is the original source for the :mod:`logging` package. The version of the
833 package available from this site is suitable for use with Python 1.5.2, 2.1.x
834 and 2.2.x, which do not include the :mod:`logging` package in the standard
841 Loggers have the following attributes and methods. Note that Loggers are never
842 instantiated directly, but always through the module-level function
843 ``logging.getLogger(name)``.
846 .. attribute:: Logger.propagate
848 If this evaluates to false, logging messages are not passed by this logger or by
849 child loggers to higher level (ancestor) loggers. The constructor sets this
853 .. method:: Logger.setLevel(lvl)
855 Sets the threshold for this logger to *lvl*. Logging messages which are less
856 severe than *lvl* will be ignored. When a logger is created, the level is set to
857 :const:`NOTSET` (which causes all messages to be processed when the logger is
858 the root logger, or delegation to the parent when the logger is a non-root
859 logger). Note that the root logger is created with level :const:`WARNING`.
861 The term "delegation to the parent" means that if a logger has a level of
862 NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
863 a level other than NOTSET is found, or the root is reached.
865 If an ancestor is found with a level other than NOTSET, then that ancestor's
866 level is treated as the effective level of the logger where the ancestor search
867 began, and is used to determine how a logging event is handled.
869 If the root is reached, and it has a level of NOTSET, then all messages will be
870 processed. Otherwise, the root's level will be used as the effective level.
873 .. method:: Logger.isEnabledFor(lvl)
875 Indicates if a message of severity *lvl* would be processed by this logger.
876 This method checks first the module-level level set by
877 ``logging.disable(lvl)`` and then the logger's effective level as determined
878 by :meth:`getEffectiveLevel`.
881 .. method:: Logger.getEffectiveLevel()
883 Indicates the effective level for this logger. If a value other than
884 :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
885 the hierarchy is traversed towards the root until a value other than
886 :const:`NOTSET` is found, and that value is returned.
889 .. method:: Logger.debug(msg[, *args[, **kwargs]])
891 Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
892 message format string, and the *args* are the arguments which are merged into
893 *msg* using the string formatting operator. (Note that this means that you can
894 use keywords in the format string, together with a single dictionary argument.)
896 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
897 which, if it does not evaluate as false, causes exception information to be
898 added to the logging message. If an exception tuple (in the format returned by
899 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
900 is called to get the exception information.
902 The other optional keyword argument is *extra* which can be used to pass a
903 dictionary which is used to populate the __dict__ of the LogRecord created for
904 the logging event with user-defined attributes. These custom attributes can then
905 be used as you like. For example, they could be incorporated into logged
906 messages. For example::
908 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
909 logging.basicConfig(format=FORMAT)
910 d = { 'clientip' : '192.168.0.1', 'user' : 'fbloggs' }
911 logger = logging.getLogger("tcpserver")
912 logger.warning("Protocol problem: %s", "connection reset", extra=d)
914 would print something like ::
916 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
918 The keys in the dictionary passed in *extra* should not clash with the keys used
919 by the logging system. (See the :class:`Formatter` documentation for more
920 information on which keys are used by the logging system.)
922 If you choose to use these attributes in logged messages, you need to exercise
923 some care. In the above example, for instance, the :class:`Formatter` has been
924 set up with a format string which expects 'clientip' and 'user' in the attribute
925 dictionary of the LogRecord. If these are missing, the message will not be
926 logged because a string formatting exception will occur. So in this case, you
927 always need to pass the *extra* dictionary with these keys.
929 While this might be annoying, this feature is intended for use in specialized
930 circumstances, such as multi-threaded servers where the same code executes in
931 many contexts, and interesting conditions which arise are dependent on this
932 context (such as remote client IP address and authenticated user name, in the
933 above example). In such circumstances, it is likely that specialized
934 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
936 .. versionchanged:: 2.5
940 .. method:: Logger.info(msg[, *args[, **kwargs]])
942 Logs a message with level :const:`INFO` on this logger. The arguments are
943 interpreted as for :meth:`debug`.
946 .. method:: Logger.warning(msg[, *args[, **kwargs]])
948 Logs a message with level :const:`WARNING` on this logger. The arguments are
949 interpreted as for :meth:`debug`.
952 .. method:: Logger.error(msg[, *args[, **kwargs]])
954 Logs a message with level :const:`ERROR` on this logger. The arguments are
955 interpreted as for :meth:`debug`.
958 .. method:: Logger.critical(msg[, *args[, **kwargs]])
960 Logs a message with level :const:`CRITICAL` on this logger. The arguments are
961 interpreted as for :meth:`debug`.
964 .. method:: Logger.log(lvl, msg[, *args[, **kwargs]])
966 Logs a message with integer level *lvl* on this logger. The other arguments are
967 interpreted as for :meth:`debug`.
970 .. method:: Logger.exception(msg[, *args])
972 Logs a message with level :const:`ERROR` on this logger. The arguments are
973 interpreted as for :meth:`debug`. Exception info is added to the logging
974 message. This method should only be called from an exception handler.
977 .. method:: Logger.addFilter(filt)
979 Adds the specified filter *filt* to this logger.
982 .. method:: Logger.removeFilter(filt)
984 Removes the specified filter *filt* from this logger.
987 .. method:: Logger.filter(record)
989 Applies this logger's filters to the record and returns a true value if the
990 record is to be processed.
993 .. method:: Logger.addHandler(hdlr)
995 Adds the specified handler *hdlr* to this logger.
998 .. method:: Logger.removeHandler(hdlr)
1000 Removes the specified handler *hdlr* from this logger.
1003 .. method:: Logger.findCaller()
1005 Finds the caller's source filename and line number. Returns the filename, line
1006 number and function name as a 3-element tuple.
1008 .. versionchanged:: 2.4
1009 The function name was added. In earlier versions, the filename and line number
1010 were returned as a 2-element tuple..
1013 .. method:: Logger.handle(record)
1015 Handles a record by passing it to all handlers associated with this logger and
1016 its ancestors (until a false value of *propagate* is found). This method is used
1017 for unpickled records received from a socket, as well as those created locally.
1018 Logger-level filtering is applied using :meth:`filter`.
1021 .. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info [, func, extra])
1023 This is a factory method which can be overridden in subclasses to create
1024 specialized :class:`LogRecord` instances.
1026 .. versionchanged:: 2.5
1027 *func* and *extra* were added.
1030 .. _minimal-example:
1035 .. versionchanged:: 2.4
1036 formerly :func:`basicConfig` did not take any keyword arguments.
1038 The :mod:`logging` package provides a lot of flexibility, and its configuration
1039 can appear daunting. This section demonstrates that simple use of the logging
1040 package is possible.
1042 The simplest example shows logging to the console::
1046 logging.debug('A debug message')
1047 logging.info('Some information')
1048 logging.warning('A shot across the bows')
1050 If you run the above script, you'll see this::
1052 WARNING:root:A shot across the bows
1054 Because no particular logger was specified, the system used the root logger. The
1055 debug and info messages didn't appear because by default, the root logger is
1056 configured to only handle messages with a severity of WARNING or above. The
1057 message format is also a configuration default, as is the output destination of
1058 the messages - ``sys.stderr``. The severity level, the message format and
1059 destination can be easily changed, as shown in the example below::
1063 logging.basicConfig(level=logging.DEBUG,
1064 format='%(asctime)s %(levelname)s %(message)s',
1065 filename='/tmp/myapp.log',
1067 logging.debug('A debug message')
1068 logging.info('Some information')
1069 logging.warning('A shot across the bows')
1071 The :meth:`basicConfig` method is used to change the configuration defaults,
1072 which results in output (written to ``/tmp/myapp.log``) which should look
1073 something like the following::
1075 2004-07-02 13:00:08,743 DEBUG A debug message
1076 2004-07-02 13:00:08,743 INFO Some information
1077 2004-07-02 13:00:08,743 WARNING A shot across the bows
1079 This time, all messages with a severity of DEBUG or above were handled, and the
1080 format of the messages was also changed, and output went to the specified file
1081 rather than the console.
1083 Formatting uses standard Python string formatting - see section
1084 :ref:`string-formatting`. The format string takes the following common
1085 specifiers. For a complete list of specifiers, consult the :class:`Formatter`
1088 +-------------------+-----------------------------------------------+
1089 | Format | Description |
1090 +===================+===============================================+
1091 | ``%(name)s`` | Name of the logger (logging channel). |
1092 +-------------------+-----------------------------------------------+
1093 | ``%(levelname)s`` | Text logging level for the message |
1094 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1095 | | ``'ERROR'``, ``'CRITICAL'``). |
1096 +-------------------+-----------------------------------------------+
1097 | ``%(asctime)s`` | Human-readable time when the |
1098 | | :class:`LogRecord` was created. By default |
1099 | | this is of the form "2003-07-08 16:49:45,896" |
1100 | | (the numbers after the comma are millisecond |
1101 | | portion of the time). |
1102 +-------------------+-----------------------------------------------+
1103 | ``%(message)s`` | The logged message. |
1104 +-------------------+-----------------------------------------------+
1106 To change the date/time format, you can pass an additional keyword parameter,
1107 *datefmt*, as in the following::
1111 logging.basicConfig(level=logging.DEBUG,
1112 format='%(asctime)s %(levelname)-8s %(message)s',
1113 datefmt='%a, %d %b %Y %H:%M:%S',
1114 filename='/temp/myapp.log',
1116 logging.debug('A debug message')
1117 logging.info('Some information')
1118 logging.warning('A shot across the bows')
1120 which would result in output like ::
1122 Fri, 02 Jul 2004 13:06:18 DEBUG A debug message
1123 Fri, 02 Jul 2004 13:06:18 INFO Some information
1124 Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows
1126 The date format string follows the requirements of :func:`strftime` - see the
1127 documentation for the :mod:`time` module.
1129 If, instead of sending logging output to the console or a file, you'd rather use
1130 a file-like object which you have created separately, you can pass it to
1131 :func:`basicConfig` using the *stream* keyword argument. Note that if both
1132 *stream* and *filename* keyword arguments are passed, the *stream* argument is
1135 Of course, you can put variable information in your output. To do this, simply
1136 have the message be a format string and pass in additional arguments containing
1137 the variable information, as in the following example::
1141 logging.basicConfig(level=logging.DEBUG,
1142 format='%(asctime)s %(levelname)-8s %(message)s',
1143 datefmt='%a, %d %b %Y %H:%M:%S',
1144 filename='/temp/myapp.log',
1146 logging.error('Pack my box with %d dozen %s', 5, 'liquor jugs')
1148 which would result in ::
1150 Wed, 21 Jul 2004 15:35:16 ERROR Pack my box with 5 dozen liquor jugs
1153 .. _multiple-destinations:
1155 Logging to multiple destinations
1156 --------------------------------
1158 Let's say you want to log to console and file with different message formats and
1159 in differing circumstances. Say you want to log messages with levels of DEBUG
1160 and higher to file, and those messages at level INFO and higher to the console.
1161 Let's also assume that the file should contain timestamps, but the console
1162 messages should not. Here's how you can achieve this::
1166 # set up logging to file - see previous section for more details
1167 logging.basicConfig(level=logging.DEBUG,
1168 format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
1169 datefmt='%m-%d %H:%M',
1170 filename='/temp/myapp.log',
1172 # define a Handler which writes INFO messages or higher to the sys.stderr
1173 console = logging.StreamHandler()
1174 console.setLevel(logging.INFO)
1175 # set a format which is simpler for console use
1176 formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
1177 # tell the handler to use this format
1178 console.setFormatter(formatter)
1179 # add the handler to the root logger
1180 logging.getLogger('').addHandler(console)
1182 # Now, we can log to the root logger, or any other logger. First the root...
1183 logging.info('Jackdaws love my big sphinx of quartz.')
1185 # Now, define a couple of other loggers which might represent areas in your
1188 logger1 = logging.getLogger('myapp.area1')
1189 logger2 = logging.getLogger('myapp.area2')
1191 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1192 logger1.info('How quickly daft jumping zebras vex.')
1193 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1194 logger2.error('The five boxing wizards jump quickly.')
1196 When you run this, on the console you will see ::
1198 root : INFO Jackdaws love my big sphinx of quartz.
1199 myapp.area1 : INFO How quickly daft jumping zebras vex.
1200 myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
1201 myapp.area2 : ERROR The five boxing wizards jump quickly.
1203 and in the file you will see something like ::
1205 10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
1206 10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1207 10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
1208 10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1209 10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
1211 As you can see, the DEBUG message only shows up in the file. The other messages
1212 are sent to both destinations.
1214 This example uses console and file handlers, but you can use any number and
1215 combination of handlers you choose.
1220 Adding contextual information to your logging output
1221 ----------------------------------------------------
1223 Sometimes you want logging output to contain contextual information in
1224 addition to the parameters passed to the logging call. For example, in a
1225 networked application, it may be desirable to log client-specific information
1226 in the log (e.g. remote client's username, or IP address). Although you could
1227 use the *extra* parameter to achieve this, it's not always convenient to pass
1228 the information in this way. While it might be tempting to create
1229 :class:`Logger` instances on a per-connection basis, this is not a good idea
1230 because these instances are not garbage collected. While this is not a problem
1231 in practice, when the number of :class:`Logger` instances is dependent on the
1232 level of granularity you want to use in logging an application, it could
1233 be hard to manage if the number of :class:`Logger` instances becomes
1234 effectively unbounded.
1236 An easy way in which you can pass contextual information to be output along
1237 with logging event information is to use the :class:`LoggerAdapter` class.
1238 This class is designed to look like a :class:`Logger`, so that you can call
1239 :meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
1240 :meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
1241 same signatures as their counterparts in :class:`Logger`, so you can use the
1242 two types of instances interchangeably.
1244 When you create an instance of :class:`LoggerAdapter`, you pass it a
1245 :class:`Logger` instance and a dict-like object which contains your contextual
1246 information. When you call one of the logging methods on an instance of
1247 :class:`LoggerAdapter`, it delegates the call to the underlying instance of
1248 :class:`Logger` passed to its constructor, and arranges to pass the contextual
1249 information in the delegated call. Here's a snippet from the code of
1250 :class:`LoggerAdapter`::
1252 def debug(self, msg, *args, **kwargs):
1254 Delegate a debug call to the underlying logger, after adding
1255 contextual information from this adapter instance.
1257 msg, kwargs = self.process(msg, kwargs)
1258 self.logger.debug(msg, *args, **kwargs)
1260 The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
1261 information is added to the logging output. It's passed the message and
1262 keyword arguments of the logging call, and it passes back (potentially)
1263 modified versions of these to use in the call to the underlying logger. The
1264 default implementation of this method leaves the message alone, but inserts
1265 an "extra" key in the keyword argument whose value is the dict-like object
1266 passed to the constructor. Of course, if you had passed an "extra" keyword
1267 argument in the call to the adapter, it will be silently overwritten.
1269 The advantage of using "extra" is that the values in the dict-like object are
1270 merged into the :class:`LogRecord` instance's __dict__, allowing you to use
1271 customized strings with your :class:`Formatter` instances which know about
1272 the keys of the dict-like object. If you need a different method, e.g. if you
1273 want to prepend or append the contextual information to the message string,
1274 you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
1275 to do what you need. Here's an example script which uses this class, which
1276 also illustrates what dict-like behaviour is needed from an arbitrary
1277 "dict-like" object for use in the constructor::
1283 An example class which shows how an arbitrary class can be used as
1284 the 'extra' context information repository passed to a LoggerAdapter.
1287 def __getitem__(self, name):
1289 To allow this instance to look like a dict.
1291 from random import choice
1293 result = choice(["127.0.0.1", "192.168.0.1"])
1294 elif name == "user":
1295 result = choice(["jim", "fred", "sheila"])
1297 result = self.__dict__.get(name, "?")
1302 To allow iteration over keys, which will be merged into
1303 the LogRecord dict before formatting and output.
1305 keys = ["ip", "user"]
1306 keys.extend(self.__dict__.keys())
1307 return keys.__iter__()
1309 if __name__ == "__main__":
1310 from random import choice
1311 levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
1312 a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"),
1313 { "ip" : "123.231.231.123", "user" : "sheila" })
1314 logging.basicConfig(level=logging.DEBUG,
1315 format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s")
1316 a1.debug("A debug message")
1317 a1.info("An info message with %s", "some parameters")
1318 a2 = logging.LoggerAdapter(logging.getLogger("d.e.f"), ConnInfo())
1320 lvl = choice(levels)
1321 lvlname = logging.getLevelName(lvl)
1322 a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters")
1324 When this script is run, the output should look something like this::
1326 2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
1327 2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
1328 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
1329 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
1330 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
1331 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
1332 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
1333 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
1334 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
1335 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
1336 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
1337 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
1339 .. versionadded:: 2.6
1341 The :class:`LoggerAdapter` class was not present in previous versions.
1344 .. _network-logging:
1346 Sending and receiving logging events across a network
1347 -----------------------------------------------------
1349 Let's say you want to send logging events across a network, and handle them at
1350 the receiving end. A simple way of doing this is attaching a
1351 :class:`SocketHandler` instance to the root logger at the sending end::
1353 import logging, logging.handlers
1355 rootLogger = logging.getLogger('')
1356 rootLogger.setLevel(logging.DEBUG)
1357 socketHandler = logging.handlers.SocketHandler('localhost',
1358 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1359 # don't bother with a formatter, since a socket handler sends the event as
1360 # an unformatted pickle
1361 rootLogger.addHandler(socketHandler)
1363 # Now, we can log to the root logger, or any other logger. First the root...
1364 logging.info('Jackdaws love my big sphinx of quartz.')
1366 # Now, define a couple of other loggers which might represent areas in your
1369 logger1 = logging.getLogger('myapp.area1')
1370 logger2 = logging.getLogger('myapp.area2')
1372 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1373 logger1.info('How quickly daft jumping zebras vex.')
1374 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1375 logger2.error('The five boxing wizards jump quickly.')
1377 At the receiving end, you can set up a receiver using the :mod:`SocketServer`
1378 module. Here is a basic working example::
1382 import logging.handlers
1387 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
1388 """Handler for a streaming logging request.
1390 This basically logs the record using whatever logging policy is
1396 Handle multiple requests - each expected to be a 4-byte length,
1397 followed by the LogRecord in pickle format. Logs the record
1398 according to whatever policy is configured locally.
1401 chunk = self.connection.recv(4)
1404 slen = struct.unpack(">L", chunk)[0]
1405 chunk = self.connection.recv(slen)
1406 while len(chunk) < slen:
1407 chunk = chunk + self.connection.recv(slen - len(chunk))
1408 obj = self.unPickle(chunk)
1409 record = logging.makeLogRecord(obj)
1410 self.handleLogRecord(record)
1412 def unPickle(self, data):
1413 return cPickle.loads(data)
1415 def handleLogRecord(self, record):
1416 # if a name is specified, we use the named logger rather than the one
1417 # implied by the record.
1418 if self.server.logname is not None:
1419 name = self.server.logname
1422 logger = logging.getLogger(name)
1423 # N.B. EVERY record gets logged. This is because Logger.handle
1424 # is normally called AFTER logger-level filtering. If you want
1425 # to do filtering, do it at the client end to save wasting
1426 # cycles and network bandwidth!
1427 logger.handle(record)
1429 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
1430 """simple TCP socket-based logging receiver suitable for testing.
1433 allow_reuse_address = 1
1435 def __init__(self, host='localhost',
1436 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1437 handler=LogRecordStreamHandler):
1438 SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
1443 def serve_until_stopped(self):
1447 rd, wr, ex = select.select([self.socket.fileno()],
1451 self.handle_request()
1455 logging.basicConfig(
1456 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1457 tcpserver = LogRecordSocketReceiver()
1458 print "About to start TCP server..."
1459 tcpserver.serve_until_stopped()
1461 if __name__ == "__main__":
1464 First run the server, and then the client. On the client side, nothing is
1465 printed on the console; on the server side, you should see something like::
1467 About to start TCP server...
1468 59 root INFO Jackdaws love my big sphinx of quartz.
1469 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1470 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1471 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1472 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1478 Handlers have the following attributes and methods. Note that :class:`Handler`
1479 is never instantiated directly; this class acts as a base for more useful
1480 subclasses. However, the :meth:`__init__` method in subclasses needs to call
1481 :meth:`Handler.__init__`.
1484 .. method:: Handler.__init__(level=NOTSET)
1486 Initializes the :class:`Handler` instance by setting its level, setting the list
1487 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1488 serializing access to an I/O mechanism.
1491 .. method:: Handler.createLock()
1493 Initializes a thread lock which can be used to serialize access to underlying
1494 I/O functionality which may not be threadsafe.
1497 .. method:: Handler.acquire()
1499 Acquires the thread lock created with :meth:`createLock`.
1502 .. method:: Handler.release()
1504 Releases the thread lock acquired with :meth:`acquire`.
1507 .. method:: Handler.setLevel(lvl)
1509 Sets the threshold for this handler to *lvl*. Logging messages which are less
1510 severe than *lvl* will be ignored. When a handler is created, the level is set
1511 to :const:`NOTSET` (which causes all messages to be processed).
1514 .. method:: Handler.setFormatter(form)
1516 Sets the :class:`Formatter` for this handler to *form*.
1519 .. method:: Handler.addFilter(filt)
1521 Adds the specified filter *filt* to this handler.
1524 .. method:: Handler.removeFilter(filt)
1526 Removes the specified filter *filt* from this handler.
1529 .. method:: Handler.filter(record)
1531 Applies this handler's filters to the record and returns a true value if the
1532 record is to be processed.
1535 .. method:: Handler.flush()
1537 Ensure all logging output has been flushed. This version does nothing and is
1538 intended to be implemented by subclasses.
1541 .. method:: Handler.close()
1543 Tidy up any resources used by the handler. This version does no output but
1544 removes the handler from an internal list of handlers which is closed when
1545 :func:`shutdown` is called. Subclasses should ensure that this gets called
1546 from overridden :meth:`close` methods.
1549 .. method:: Handler.handle(record)
1551 Conditionally emits the specified logging record, depending on filters which may
1552 have been added to the handler. Wraps the actual emission of the record with
1553 acquisition/release of the I/O thread lock.
1556 .. method:: Handler.handleError(record)
1558 This method should be called from handlers when an exception is encountered
1559 during an :meth:`emit` call. By default it does nothing, which means that
1560 exceptions get silently ignored. This is what is mostly wanted for a logging
1561 system - most users will not care about errors in the logging system, they are
1562 more interested in application errors. You could, however, replace this with a
1563 custom handler if you wish. The specified record is the one which was being
1564 processed when the exception occurred.
1567 .. method:: Handler.format(record)
1569 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1570 default formatter for the module.
1573 .. method:: Handler.emit(record)
1575 Do whatever it takes to actually log the specified logging record. This version
1576 is intended to be implemented by subclasses and so raises a
1577 :exc:`NotImplementedError`.
1583 The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1584 sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1585 file-like object (or, more precisely, any object which supports :meth:`write`
1586 and :meth:`flush` methods).
1589 .. class:: StreamHandler([strm])
1591 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1592 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1596 .. method:: emit(record)
1598 If a formatter is specified, it is used to format the record. The record
1599 is then written to the stream with a trailing newline. If exception
1600 information is present, it is formatted using
1601 :func:`traceback.print_exception` and appended to the stream.
1606 Flushes the stream by calling its :meth:`flush` method. Note that the
1607 :meth:`close` method is inherited from :class:`Handler` and so does
1608 no output, so an explicit :meth:`flush` call may be needed at times.
1614 The :class:`FileHandler` class, located in the core :mod:`logging` package,
1615 sends logging output to a disk file. It inherits the output functionality from
1616 :class:`StreamHandler`.
1619 .. class:: FileHandler(filename[, mode[, encoding[, delay]]])
1621 Returns a new instance of the :class:`FileHandler` class. The specified file is
1622 opened and used as the stream for logging. If *mode* is not specified,
1623 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1624 with that encoding. If *delay* is true, then file opening is deferred until the
1625 first call to :meth:`emit`. By default, the file grows indefinitely.
1633 .. method:: emit(record)
1635 Outputs the record to the file.
1641 .. versionadded:: 2.7
1643 The :class:`NullHandler` class, located in the core :mod:`logging` package,
1644 does not do any formatting or output. It is essentially a "no-op" handler
1645 for use by library developers.
1648 .. class:: NullHandler()
1650 Returns a new instance of the :class:`NullHandler` class.
1653 .. method:: emit(record)
1655 This method does nothing.
1657 See :ref:`library-config` for more information on how to use
1658 :class:`NullHandler`.
1663 .. versionadded:: 2.6
1665 .. currentmodule:: logging.handlers
1667 The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1668 module, is a :class:`FileHandler` which watches the file it is logging to. If
1669 the file changes, it is closed and reopened using the file name.
1671 A file change can happen because of usage of programs such as *newsyslog* and
1672 *logrotate* which perform log file rotation. This handler, intended for use
1673 under Unix/Linux, watches the file to see if it has changed since the last emit.
1674 (A file is deemed to have changed if its device or inode have changed.) If the
1675 file has changed, the old file stream is closed, and the file opened to get a
1678 This handler is not appropriate for use under Windows, because under Windows
1679 open log files cannot be moved or renamed - logging opens the files with
1680 exclusive locks - and so there is no need for such a handler. Furthermore,
1681 *ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1685 .. class:: WatchedFileHandler(filename[,mode[, encoding[, delay]]])
1687 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1688 file is opened and used as the stream for logging. If *mode* is not specified,
1689 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
1690 with that encoding. If *delay* is true, then file opening is deferred until the
1691 first call to :meth:`emit`. By default, the file grows indefinitely.
1694 .. method:: emit(record)
1696 Outputs the record to the file, but first checks to see if the file has
1697 changed. If it has, the existing stream is flushed and closed and the
1698 file opened again, before outputting the record to the file.
1704 The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1705 module, supports rotation of disk log files.
1708 .. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount[, encoding[, delay]]]]])
1710 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1711 file is opened and used as the stream for logging. If *mode* is not specified,
1712 ``'a'`` is used. If *encoding* is not *None*, it is used to open the file
1713 with that encoding. If *delay* is true, then file opening is deferred until the
1714 first call to :meth:`emit`. By default, the file grows indefinitely.
1716 You can use the *maxBytes* and *backupCount* values to allow the file to
1717 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1718 the file is closed and a new file is silently opened for output. Rollover occurs
1719 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1720 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1721 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1722 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1723 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1724 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1725 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1726 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1727 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1730 .. method:: doRollover()
1732 Does a rollover, as described above.
1735 .. method:: emit(record)
1737 Outputs the record to the file, catering for rollover as described
1741 TimedRotatingFileHandler
1742 ^^^^^^^^^^^^^^^^^^^^^^^^
1744 The :class:`TimedRotatingFileHandler` class, located in the
1745 :mod:`logging.handlers` module, supports rotation of disk log files at certain
1749 .. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount[, encoding[, delay[, utc]]]]]])
1751 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1752 specified file is opened and used as the stream for logging. On rotating it also
1753 sets the filename suffix. Rotating happens based on the product of *when* and
1756 You can use the *when* to specify the type of *interval*. The list of possible
1757 values is below. Note that they are not case sensitive.
1759 +----------------+-----------------------+
1760 | Value | Type of interval |
1761 +================+=======================+
1762 | ``'S'`` | Seconds |
1763 +----------------+-----------------------+
1764 | ``'M'`` | Minutes |
1765 +----------------+-----------------------+
1767 +----------------+-----------------------+
1769 +----------------+-----------------------+
1770 | ``'W'`` | Week day (0=Monday) |
1771 +----------------+-----------------------+
1772 | ``'midnight'`` | Roll over at midnight |
1773 +----------------+-----------------------+
1775 The system will save old log files by appending extensions to the filename.
1776 The extensions are date-and-time based, using the strftime format
1777 ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on the
1779 If the *utc* argument is true, times in UTC will be used; otherwise
1782 If *backupCount* is nonzero, at most *backupCount* files
1783 will be kept, and if more would be created when rollover occurs, the oldest
1784 one is deleted. The deletion logic uses the interval to determine which
1785 files to delete, so changing the interval may leave old files lying around.
1788 .. method:: doRollover()
1790 Does a rollover, as described above.
1793 .. method:: emit(record)
1795 Outputs the record to the file, catering for rollover as described above.
1801 The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1802 sends logging output to a network socket. The base class uses a TCP socket.
1805 .. class:: SocketHandler(host, port)
1807 Returns a new instance of the :class:`SocketHandler` class intended to
1808 communicate with a remote machine whose address is given by *host* and *port*.
1818 Pickles the record's attribute dictionary and writes it to the socket in
1819 binary format. If there is an error with the socket, silently drops the
1820 packet. If the connection was previously lost, re-establishes the
1821 connection. To unpickle the record at the receiving end into a
1822 :class:`LogRecord`, use the :func:`makeLogRecord` function.
1825 .. method:: handleError()
1827 Handles an error which has occurred during :meth:`emit`. The most likely
1828 cause is a lost connection. Closes the socket so that we can retry on the
1832 .. method:: makeSocket()
1834 This is a factory method which allows subclasses to define the precise
1835 type of socket they want. The default implementation creates a TCP socket
1836 (:const:`socket.SOCK_STREAM`).
1839 .. method:: makePickle(record)
1841 Pickles the record's attribute dictionary in binary format with a length
1842 prefix, and returns it ready for transmission across the socket.
1845 .. method:: send(packet)
1847 Send a pickled string *packet* to the socket. This function allows for
1848 partial sends which can happen when the network is busy.
1854 The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1855 module, inherits from :class:`SocketHandler` to support sending logging messages
1859 .. class:: DatagramHandler(host, port)
1861 Returns a new instance of the :class:`DatagramHandler` class intended to
1862 communicate with a remote machine whose address is given by *host* and *port*.
1867 Pickles the record's attribute dictionary and writes it to the socket in
1868 binary format. If there is an error with the socket, silently drops the
1869 packet. To unpickle the record at the receiving end into a
1870 :class:`LogRecord`, use the :func:`makeLogRecord` function.
1873 .. method:: makeSocket()
1875 The factory method of :class:`SocketHandler` is here overridden to create
1876 a UDP socket (:const:`socket.SOCK_DGRAM`).
1881 Send a pickled string to a socket.
1887 The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1888 supports sending logging messages to a remote or local Unix syslog.
1891 .. class:: SysLogHandler([address[, facility]])
1893 Returns a new instance of the :class:`SysLogHandler` class intended to
1894 communicate with a remote Unix machine whose address is given by *address* in
1895 the form of a ``(host, port)`` tuple. If *address* is not specified,
1896 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1897 alternative to providing a ``(host, port)`` tuple is providing an address as a
1898 string, for example "/dev/log". In this case, a Unix domain socket is used to
1899 send the message to the syslog. If *facility* is not specified,
1900 :const:`LOG_USER` is used.
1905 Closes the socket to the remote host.
1908 .. method:: emit(record)
1910 The record is formatted, and then sent to the syslog server. If exception
1911 information is present, it is *not* sent to the server.
1914 .. method:: encodePriority(facility, priority)
1916 Encodes the facility and priority into an integer. You can pass in strings
1917 or integers - if strings are passed, internal mapping dictionaries are
1918 used to convert them to integers.
1924 The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1925 module, supports sending logging messages to a local Windows NT, Windows 2000 or
1926 Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1927 extensions for Python installed.
1930 .. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1932 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1933 used to define the application name as it appears in the event log. An
1934 appropriate registry entry is created using this name. The *dllname* should give
1935 the fully qualified pathname of a .dll or .exe which contains message
1936 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1937 - this is installed with the Win32 extensions and contains some basic
1938 placeholder message definitions. Note that use of these placeholders will make
1939 your event logs big, as the entire message source is held in the log. If you
1940 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1941 contains the message definitions you want to use in the event log). The
1942 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1943 defaults to ``'Application'``.
1948 At this point, you can remove the application name from the registry as a
1949 source of event log entries. However, if you do this, you will not be able
1950 to see the events as you intended in the Event Log Viewer - it needs to be
1951 able to access the registry to get the .dll name. The current version does
1955 .. method:: emit(record)
1957 Determines the message ID, event category and event type, and then logs
1958 the message in the NT event log.
1961 .. method:: getEventCategory(record)
1963 Returns the event category for the record. Override this if you want to
1964 specify your own categories. This version returns 0.
1967 .. method:: getEventType(record)
1969 Returns the event type for the record. Override this if you want to
1970 specify your own types. This version does a mapping using the handler's
1971 typemap attribute, which is set up in :meth:`__init__` to a dictionary
1972 which contains mappings for :const:`DEBUG`, :const:`INFO`,
1973 :const:`WARNING`, :const:`ERROR` and :const:`CRITICAL`. If you are using
1974 your own levels, you will either need to override this method or place a
1975 suitable dictionary in the handler's *typemap* attribute.
1978 .. method:: getMessageID(record)
1980 Returns the message ID for the record. If you are using your own messages,
1981 you could do this by having the *msg* passed to the logger being an ID
1982 rather than a format string. Then, in here, you could use a dictionary
1983 lookup to get the message ID. This version returns 1, which is the base
1984 message ID in :file:`win32service.pyd`.
1990 The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1991 supports sending logging messages to an email address via SMTP.
1994 .. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1996 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1997 initialized with the from and to addresses and subject line of the email. The
1998 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1999 the (host, port) tuple format for the *mailhost* argument. If you use a string,
2000 the standard SMTP port is used. If your SMTP server requires authentication, you
2001 can specify a (username, password) tuple for the *credentials* argument.
2003 .. versionchanged:: 2.6
2004 *credentials* was added.
2007 .. method:: emit(record)
2009 Formats the record and sends it to the specified addressees.
2012 .. method:: getSubject(record)
2014 If you want to specify a subject line which is record-dependent, override
2021 The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
2022 supports buffering of logging records in memory, periodically flushing them to a
2023 :dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
2024 event of a certain severity or greater is seen.
2026 :class:`MemoryHandler` is a subclass of the more general
2027 :class:`BufferingHandler`, which is an abstract class. This buffers logging
2028 records in memory. Whenever each record is added to the buffer, a check is made
2029 by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
2030 should, then :meth:`flush` is expected to do the needful.
2033 .. class:: BufferingHandler(capacity)
2035 Initializes the handler with a buffer of the specified capacity.
2038 .. method:: emit(record)
2040 Appends the record to the buffer. If :meth:`shouldFlush` returns true,
2041 calls :meth:`flush` to process the buffer.
2046 You can override this to implement custom flushing behavior. This version
2047 just zaps the buffer to empty.
2050 .. method:: shouldFlush(record)
2052 Returns true if the buffer is up to capacity. This method can be
2053 overridden to implement custom flushing strategies.
2056 .. class:: MemoryHandler(capacity[, flushLevel [, target]])
2058 Returns a new instance of the :class:`MemoryHandler` class. The instance is
2059 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
2060 :const:`ERROR` is used. If no *target* is specified, the target will need to be
2061 set using :meth:`setTarget` before this handler does anything useful.
2066 Calls :meth:`flush`, sets the target to :const:`None` and clears the
2072 For a :class:`MemoryHandler`, flushing means just sending the buffered
2073 records to the target, if there is one. Override if you want different
2077 .. method:: setTarget(target)
2079 Sets the target handler for this handler.
2082 .. method:: shouldFlush(record)
2084 Checks for buffer full or a record at the *flushLevel* or higher.
2090 The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
2091 supports sending logging messages to a Web server, using either ``GET`` or
2095 .. class:: HTTPHandler(host, url[, method])
2097 Returns a new instance of the :class:`HTTPHandler` class. The instance is
2098 initialized with a host address, url and HTTP method. The *host* can be of the
2099 form ``host:port``, should you need to use a specific port number. If no
2100 *method* is specified, ``GET`` is used.
2103 .. method:: emit(record)
2105 Sends the record to the Web server as an URL-encoded dictionary.
2108 .. _formatter-objects:
2113 .. currentmodule:: logging
2115 :class:`Formatter`\ s have the following attributes and methods. They are
2116 responsible for converting a :class:`LogRecord` to (usually) a string which can
2117 be interpreted by either a human or an external system. The base
2118 :class:`Formatter` allows a formatting string to be specified. If none is
2119 supplied, the default value of ``'%(message)s'`` is used.
2121 A Formatter can be initialized with a format string which makes use of knowledge
2122 of the :class:`LogRecord` attributes - such as the default value mentioned above
2123 making use of the fact that the user's message and arguments are pre-formatted
2124 into a :class:`LogRecord`'s *message* attribute. This format string contains
2125 standard python %-style mapping keys. See section :ref:`string-formatting`
2126 for more information on string formatting.
2128 Currently, the useful mapping keys in a :class:`LogRecord` are:
2130 +-------------------------+-----------------------------------------------+
2131 | Format | Description |
2132 +=========================+===============================================+
2133 | ``%(name)s`` | Name of the logger (logging channel). |
2134 +-------------------------+-----------------------------------------------+
2135 | ``%(levelno)s`` | Numeric logging level for the message |
2136 | | (:const:`DEBUG`, :const:`INFO`, |
2137 | | :const:`WARNING`, :const:`ERROR`, |
2138 | | :const:`CRITICAL`). |
2139 +-------------------------+-----------------------------------------------+
2140 | ``%(levelname)s`` | Text logging level for the message |
2141 | | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
2142 | | ``'ERROR'``, ``'CRITICAL'``). |
2143 +-------------------------+-----------------------------------------------+
2144 | ``%(pathname)s`` | Full pathname of the source file where the |
2145 | | logging call was issued (if available). |
2146 +-------------------------+-----------------------------------------------+
2147 | ``%(filename)s`` | Filename portion of pathname. |
2148 +-------------------------+-----------------------------------------------+
2149 | ``%(module)s`` | Module (name portion of filename). |
2150 +-------------------------+-----------------------------------------------+
2151 | ``%(funcName)s`` | Name of function containing the logging call. |
2152 +-------------------------+-----------------------------------------------+
2153 | ``%(lineno)d`` | Source line number where the logging call was |
2154 | | issued (if available). |
2155 +-------------------------+-----------------------------------------------+
2156 | ``%(created)f`` | Time when the :class:`LogRecord` was created |
2157 | | (as returned by :func:`time.time`). |
2158 +-------------------------+-----------------------------------------------+
2159 | ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
2160 | | created, relative to the time the logging |
2161 | | module was loaded. |
2162 +-------------------------+-----------------------------------------------+
2163 | ``%(asctime)s`` | Human-readable time when the |
2164 | | :class:`LogRecord` was created. By default |
2165 | | this is of the form "2003-07-08 16:49:45,896" |
2166 | | (the numbers after the comma are millisecond |
2167 | | portion of the time). |
2168 +-------------------------+-----------------------------------------------+
2169 | ``%(msecs)d`` | Millisecond portion of the time when the |
2170 | | :class:`LogRecord` was created. |
2171 +-------------------------+-----------------------------------------------+
2172 | ``%(thread)d`` | Thread ID (if available). |
2173 +-------------------------+-----------------------------------------------+
2174 | ``%(threadName)s`` | Thread name (if available). |
2175 +-------------------------+-----------------------------------------------+
2176 | ``%(process)d`` | Process ID (if available). |
2177 +-------------------------+-----------------------------------------------+
2178 | ``%(message)s`` | The logged message, computed as ``msg % |
2180 +-------------------------+-----------------------------------------------+
2182 .. versionchanged:: 2.5
2183 *funcName* was added.
2186 .. class:: Formatter([fmt[, datefmt]])
2188 Returns a new instance of the :class:`Formatter` class. The instance is
2189 initialized with a format string for the message as a whole, as well as a format
2190 string for the date/time portion of a message. If no *fmt* is specified,
2191 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
2195 .. method:: format(record)
2197 The record's attribute dictionary is used as the operand to a string
2198 formatting operation. Returns the resulting string. Before formatting the
2199 dictionary, a couple of preparatory steps are carried out. The *message*
2200 attribute of the record is computed using *msg* % *args*. If the
2201 formatting string contains ``'(asctime)'``, :meth:`formatTime` is called
2202 to format the event time. If there is exception information, it is
2203 formatted using :meth:`formatException` and appended to the message. Note
2204 that the formatted exception information is cached in attribute
2205 *exc_text*. This is useful because the exception information can be
2206 pickled and sent across the wire, but you should be careful if you have
2207 more than one :class:`Formatter` subclass which customizes the formatting
2208 of exception information. In this case, you will have to clear the cached
2209 value after a formatter has done its formatting, so that the next
2210 formatter to handle the event doesn't use the cached value but
2211 recalculates it afresh.
2214 .. method:: formatTime(record[, datefmt])
2216 This method should be called from :meth:`format` by a formatter which
2217 wants to make use of a formatted time. This method can be overridden in
2218 formatters to provide for any specific requirement, but the basic behavior
2219 is as follows: if *datefmt* (a string) is specified, it is used with
2220 :func:`time.strftime` to format the creation time of the
2221 record. Otherwise, the ISO8601 format is used. The resulting string is
2225 .. method:: formatException(exc_info)
2227 Formats the specified exception information (a standard exception tuple as
2228 returned by :func:`sys.exc_info`) as a string. This default implementation
2229 just uses :func:`traceback.print_exception`. The resulting string is
2236 :class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
2237 more sophisticated filtering than is provided by levels. The base filter class
2238 only allows events which are below a certain point in the logger hierarchy. For
2239 example, a filter initialized with "A.B" will allow events logged by loggers
2240 "A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
2241 initialized with the empty string, all events are passed.
2244 .. class:: Filter([name])
2246 Returns an instance of the :class:`Filter` class. If *name* is specified, it
2247 names a logger which, together with its children, will have its events allowed
2248 through the filter. If no name is specified, allows every event.
2251 .. method:: filter(record)
2253 Is the specified record to be logged? Returns zero for no, nonzero for
2254 yes. If deemed appropriate, the record may be modified in-place by this
2261 :class:`LogRecord` instances are created every time something is logged. They
2262 contain all the information pertinent to the event being logged. The main
2263 information passed in is in msg and args, which are combined using msg % args to
2264 create the message field of the record. The record also includes information
2265 such as when the record was created, the source line where the logging call was
2266 made, and any exception information to be logged.
2269 .. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2271 Returns an instance of :class:`LogRecord` initialized with interesting
2272 information. The *name* is the logger name; *lvl* is the numeric level;
2273 *pathname* is the absolute pathname of the source file in which the logging
2274 call was made; *lineno* is the line number in that file where the logging
2275 call is found; *msg* is the user-supplied message (a format string); *args*
2276 is the tuple which, together with *msg*, makes up the user message; and
2277 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2278 (or :const:`None`, if no exception information is available). The *func* is
2279 the name of the function from which the logging call was made. If not
2280 specified, it defaults to ``None``.
2282 .. versionchanged:: 2.5
2286 .. method:: getMessage()
2288 Returns the message for this :class:`LogRecord` instance after merging any
2289 user-supplied arguments with the message.
2292 LoggerAdapter Objects
2293 ---------------------
2295 .. versionadded:: 2.6
2297 :class:`LoggerAdapter` instances are used to conveniently pass contextual
2298 information into logging calls. For a usage example , see the section on
2299 `adding contextual information to your logging output`__.
2303 .. class:: LoggerAdapter(logger, extra)
2305 Returns an instance of :class:`LoggerAdapter` initialized with an
2306 underlying :class:`Logger` instance and a dict-like object.
2308 .. method:: process(msg, kwargs)
2310 Modifies the message and/or keyword arguments passed to a logging call in
2311 order to insert contextual information. This implementation takes the object
2312 passed as *extra* to the constructor and adds it to *kwargs* using key
2313 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
2314 (possibly modified) versions of the arguments passed in.
2316 In addition to the above, :class:`LoggerAdapter` supports all the logging
2317 methods of :class:`Logger`, i.e. :meth:`debug`, :meth:`info`, :meth:`warning`,
2318 :meth:`error`, :meth:`exception`, :meth:`critical` and :meth:`log`. These
2319 methods have the same signatures as their counterparts in :class:`Logger`, so
2320 you can use the two types of instances interchangeably.
2326 The logging module is intended to be thread-safe without any special work
2327 needing to be done by its clients. It achieves this though using threading
2328 locks; there is one lock to serialize access to the module's shared data, and
2329 each handler also creates a lock to serialize access to its underlying I/O.
2336 .. _logging-config-api:
2338 Configuration functions
2339 ^^^^^^^^^^^^^^^^^^^^^^^
2341 The following functions configure the logging module. They are located in the
2342 :mod:`logging.config` module. Their use is optional --- you can configure the
2343 logging module using these functions or by making calls to the main API (defined
2344 in :mod:`logging` itself) and defining handlers which are declared either in
2345 :mod:`logging` or :mod:`logging.handlers`.
2348 .. function:: fileConfig(fname[, defaults])
2350 Reads the logging configuration from a :mod:`ConfigParser`\-format file named
2351 *fname*. This function can be called several times from an application,
2352 allowing an end user the ability to select from various pre-canned
2353 configurations (if the developer provides a mechanism to present the choices
2354 and load the chosen configuration). Defaults to be passed to the ConfigParser
2355 can be specified in the *defaults* argument.
2358 .. function:: listen([port])
2360 Starts up a socket server on the specified port, and listens for new
2361 configurations. If no port is specified, the module's default
2362 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2363 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2364 :class:`Thread` instance on which you can call :meth:`start` to start the
2365 server, and which you can :meth:`join` when appropriate. To stop the server,
2366 call :func:`stopListening`.
2368 To send a configuration to the socket, read in the configuration file and
2369 send it to the socket as a string of bytes preceded by a four-byte length
2370 string packed in binary using ``struct.pack('>L', n)``.
2373 .. function:: stopListening()
2375 Stops the listening server which was created with a call to :func:`listen`.
2376 This is typically called before calling :meth:`join` on the return value from
2380 .. _logging-config-fileformat:
2382 Configuration file format
2383 ^^^^^^^^^^^^^^^^^^^^^^^^^
2385 The configuration file format understood by :func:`fileConfig` is based on
2386 :mod:`ConfigParser` functionality. The file must contain sections called
2387 ``[loggers]``, ``[handlers]`` and ``[formatters]`` which identify by name the
2388 entities of each type which are defined in the file. For each such entity,
2389 there is a separate section which identifies how that entity is configured.
2390 Thus, for a logger named ``log01`` in the ``[loggers]`` section, the relevant
2391 configuration details are held in a section ``[logger_log01]``. Similarly, a
2392 handler called ``hand01`` in the ``[handlers]`` section will have its
2393 configuration held in a section called ``[handler_hand01]``, while a formatter
2394 called ``form01`` in the ``[formatters]`` section will have its configuration
2395 specified in a section called ``[formatter_form01]``. The root logger
2396 configuration must be specified in a section called ``[logger_root]``.
2398 Examples of these sections in the file are given below. ::
2401 keys=root,log02,log03,log04,log05,log06,log07
2404 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2407 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2409 The root logger must specify a level and a list of handlers. An example of a
2410 root logger section is given below. ::
2416 The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2417 ``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2418 logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2419 package's namespace.
2421 The ``handlers`` entry is a comma-separated list of handler names, which must
2422 appear in the ``[handlers]`` section. These names must appear in the
2423 ``[handlers]`` section and have corresponding sections in the configuration
2426 For loggers other than the root logger, some additional information is required.
2427 This is illustrated by the following example. ::
2433 qualname=compiler.parser
2435 The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2436 except that if a non-root logger's level is specified as ``NOTSET``, the system
2437 consults loggers higher up the hierarchy to determine the effective level of the
2438 logger. The ``propagate`` entry is set to 1 to indicate that messages must
2439 propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2440 indicate that messages are **not** propagated to handlers up the hierarchy. The
2441 ``qualname`` entry is the hierarchical channel name of the logger, that is to
2442 say the name used by the application to get the logger.
2444 Sections which specify handler configuration are exemplified by the following.
2453 The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2454 in the ``logging`` package's namespace). The ``level`` is interpreted as for
2455 loggers, and ``NOTSET`` is taken to mean "log everything".
2457 .. versionchanged:: 2.6
2458 Added support for resolving the handler's class as a dotted module and class
2461 The ``formatter`` entry indicates the key name of the formatter for this
2462 handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2463 If a name is specified, it must appear in the ``[formatters]`` section and have
2464 a corresponding section in the configuration file.
2466 The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2467 package's namespace, is the list of arguments to the constructor for the handler
2468 class. Refer to the constructors for the relevant handlers, or to the examples
2469 below, to see how typical entries are constructed. ::
2475 args=('python.log', 'w')
2478 class=handlers.SocketHandler
2481 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2484 class=handlers.DatagramHandler
2487 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2490 class=handlers.SysLogHandler
2493 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2496 class=handlers.NTEventLogHandler
2499 args=('Python Application', '', 'Application')
2502 class=handlers.SMTPHandler
2505 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2508 class=handlers.MemoryHandler
2515 class=handlers.HTTPHandler
2518 args=('localhost:9022', '/log', 'GET')
2520 Sections which specify formatter configuration are typified by the following. ::
2523 format=F1 %(asctime)s %(levelname)s %(message)s
2525 class=logging.Formatter
2527 The ``format`` entry is the overall format string, and the ``datefmt`` entry is
2528 the :func:`strftime`\ -compatible date/time format string. If empty, the
2529 package substitutes ISO8601 format date/times, which is almost equivalent to
2530 specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2531 also specifies milliseconds, which are appended to the result of using the above
2532 format string, with a comma separator. An example time in ISO8601 format is
2533 ``2003-01-23 00:29:50,411``.
2535 The ``class`` entry is optional. It indicates the name of the formatter's class
2536 (as a dotted module and class name.) This option is useful for instantiating a
2537 :class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2538 exception tracebacks in an expanded or condensed format.
2541 Configuration server example
2542 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2544 Here is an example of a module using the logging configuration server::
2547 import logging.config
2551 # read initial config file
2552 logging.config.fileConfig("logging.conf")
2554 # create and start listener on port 9999
2555 t = logging.config.listen(9999)
2558 logger = logging.getLogger("simpleExample")
2561 # loop through logging calls to see the difference
2562 # new configurations make, until Ctrl+C is pressed
2564 logger.debug("debug message")
2565 logger.info("info message")
2566 logger.warn("warn message")
2567 logger.error("error message")
2568 logger.critical("critical message")
2570 except KeyboardInterrupt:
2572 logging.config.stopListening()
2575 And here is a script that takes a filename and sends that file to the server,
2576 properly preceded with the binary-encoded length, as the new logging
2579 #!/usr/bin/env python
2580 import socket, sys, struct
2582 data_to_send = open(sys.argv[1], "r").read()
2586 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2587 print "connecting..."
2588 s.connect((HOST, PORT))
2589 print "sending config..."
2590 s.send(struct.pack(">L", len(data_to_send)))
2591 s.send(data_to_send)
2599 Multiple handlers and formatters
2600 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2602 Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2603 or maximum quota for the number of handlers you may add. Sometimes it will be
2604 beneficial for an application to log all messages of all severities to a text
2605 file while simultaneously logging errors or above to the console. To set this
2606 up, simply configure the appropriate handlers. The logging calls in the
2607 application code will remain unchanged. Here is a slight modification to the
2608 previous simple module-based configuration example::
2612 logger = logging.getLogger("simple_example")
2613 logger.setLevel(logging.DEBUG)
2614 # create file handler which logs even debug messages
2615 fh = logging.FileHandler("spam.log")
2616 fh.setLevel(logging.DEBUG)
2617 # create console handler with a higher log level
2618 ch = logging.StreamHandler()
2619 ch.setLevel(logging.ERROR)
2620 # create formatter and add it to the handlers
2621 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2622 ch.setFormatter(formatter)
2623 fh.setFormatter(formatter)
2624 # add the handlers to logger
2625 logger.addHandler(ch)
2626 logger.addHandler(fh)
2628 # "application" code
2629 logger.debug("debug message")
2630 logger.info("info message")
2631 logger.warn("warn message")
2632 logger.error("error message")
2633 logger.critical("critical message")
2635 Notice that the "application" code does not care about multiple handlers. All
2636 that changed was the addition and configuration of a new handler named *fh*.
2638 The ability to create new handlers with higher- or lower-severity filters can be
2639 very helpful when writing and testing an application. Instead of using many
2640 ``print`` statements for debugging, use ``logger.debug``: Unlike the print
2641 statements, which you will have to delete or comment out later, the logger.debug
2642 statements can remain intact in the source code and remain dormant until you
2643 need them again. At that time, the only change that needs to happen is to
2644 modify the severity level of the logger and/or handler to debug.
2647 Using logging in multiple modules
2648 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2650 It was mentioned above that multiple calls to
2651 ``logging.getLogger('someLogger')`` return a reference to the same logger
2652 object. This is true not only within the same module, but also across modules
2653 as long as it is in the same Python interpreter process. It is true for
2654 references to the same object; additionally, application code can define and
2655 configure a parent logger in one module and create (but not configure) a child
2656 logger in a separate module, and all logger calls to the child will pass up to
2657 the parent. Here is a main module::
2660 import auxiliary_module
2662 # create logger with "spam_application"
2663 logger = logging.getLogger("spam_application")
2664 logger.setLevel(logging.DEBUG)
2665 # create file handler which logs even debug messages
2666 fh = logging.FileHandler("spam.log")
2667 fh.setLevel(logging.DEBUG)
2668 # create console handler with a higher log level
2669 ch = logging.StreamHandler()
2670 ch.setLevel(logging.ERROR)
2671 # create formatter and add it to the handlers
2672 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2673 fh.setFormatter(formatter)
2674 ch.setFormatter(formatter)
2675 # add the handlers to the logger
2676 logger.addHandler(fh)
2677 logger.addHandler(ch)
2679 logger.info("creating an instance of auxiliary_module.Auxiliary")
2680 a = auxiliary_module.Auxiliary()
2681 logger.info("created an instance of auxiliary_module.Auxiliary")
2682 logger.info("calling auxiliary_module.Auxiliary.do_something")
2684 logger.info("finished auxiliary_module.Auxiliary.do_something")
2685 logger.info("calling auxiliary_module.some_function()")
2686 auxiliary_module.some_function()
2687 logger.info("done with auxiliary_module.some_function()")
2689 Here is the auxiliary module::
2694 module_logger = logging.getLogger("spam_application.auxiliary")
2698 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2699 self.logger.info("creating an instance of Auxiliary")
2700 def do_something(self):
2701 self.logger.info("doing something")
2703 self.logger.info("done doing something")
2705 def some_function():
2706 module_logger.info("received a call to \"some_function\"")
2708 The output looks like this::
2710 2005-03-23 23:47:11,663 - spam_application - INFO -
2711 creating an instance of auxiliary_module.Auxiliary
2712 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
2713 creating an instance of Auxiliary
2714 2005-03-23 23:47:11,665 - spam_application - INFO -
2715 created an instance of auxiliary_module.Auxiliary
2716 2005-03-23 23:47:11,668 - spam_application - INFO -
2717 calling auxiliary_module.Auxiliary.do_something
2718 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
2720 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
2721 done doing something
2722 2005-03-23 23:47:11,670 - spam_application - INFO -
2723 finished auxiliary_module.Auxiliary.do_something
2724 2005-03-23 23:47:11,671 - spam_application - INFO -
2725 calling auxiliary_module.some_function()
2726 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
2727 received a call to "some_function"
2728 2005-03-23 23:47:11,673 - spam_application - INFO -
2729 done with auxiliary_module.some_function()