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Georg Brandl8ec7f652007-08-15 14:28:01 +00001:mod:`logging` --- Logging facility for Python
2==============================================
3
4.. module:: logging
5 :synopsis: Flexible error logging system for applications.
6
7
8.. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
9.. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com>
10
11
Georg Brandl8ec7f652007-08-15 14:28:01 +000012.. index:: pair: Errors; logging
13
14.. versionadded:: 2.3
15
16This module defines functions and classes which implement a flexible error
17logging system for applications.
18
19Logging is performed by calling methods on instances of the :class:`Logger`
20class (hereafter called :dfn:`loggers`). Each instance has a name, and they are
Georg Brandla7395032007-10-21 12:15:05 +000021conceptually arranged in a namespace hierarchy using dots (periods) as
Georg Brandl8ec7f652007-08-15 14:28:01 +000022separators. For example, a logger named "scan" is the parent of loggers
23"scan.text", "scan.html" and "scan.pdf". Logger names can be anything you want,
24and indicate the area of an application in which a logged message originates.
25
26Logged messages also have levels of importance associated with them. The default
27levels provided are :const:`DEBUG`, :const:`INFO`, :const:`WARNING`,
28:const:`ERROR` and :const:`CRITICAL`. As a convenience, you indicate the
29importance of a logged message by calling an appropriate method of
30:class:`Logger`. The methods are :meth:`debug`, :meth:`info`, :meth:`warning`,
31:meth:`error` and :meth:`critical`, which mirror the default levels. You are not
32constrained to use these levels: you can specify your own and use a more general
33:class:`Logger` method, :meth:`log`, which takes an explicit level argument.
34
Georg Brandlc37f2882007-12-04 17:46:27 +000035
36Logging tutorial
37----------------
38
39The key benefit of having the logging API provided by a standard library module
40is that all Python modules can participate in logging, so your application log
41can include messages from third-party modules.
42
43It is, of course, possible to log messages with different verbosity levels or to
44different destinations. Support for writing log messages to files, HTTP
45GET/POST locations, email via SMTP, generic sockets, or OS-specific logging
Georg Brandl907a7202008-02-22 12:31:45 +000046mechanisms are all supported by the standard module. You can also create your
Georg Brandlc37f2882007-12-04 17:46:27 +000047own log destination class if you have special requirements not met by any of the
48built-in classes.
49
50Simple examples
51^^^^^^^^^^^^^^^
52
53.. sectionauthor:: Doug Hellmann
54.. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>)
55
56Most applications are probably going to want to log to a file, so let's start
57with that case. Using the :func:`basicConfig` function, we can set up the
58default handler so that debug messages are written to a file::
59
60 import logging
61 LOG_FILENAME = '/tmp/logging_example.out'
62 logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,)
63
64 logging.debug('This message should go to the log file')
65
66And now if we open the file and look at what we have, we should find the log
67message::
68
69 DEBUG:root:This message should go to the log file
70
71If you run the script repeatedly, the additional log messages are appended to
72the file. To create a new file each time, you can pass a filemode argument to
73:func:`basicConfig` with a value of ``'w'``. Rather than managing the file size
74yourself, though, it is simpler to use a :class:`RotatingFileHandler`::
75
76 import glob
77 import logging
78 import logging.handlers
79
80 LOG_FILENAME = '/tmp/logging_rotatingfile_example.out'
81
82 # Set up a specific logger with our desired output level
83 my_logger = logging.getLogger('MyLogger')
84 my_logger.setLevel(logging.DEBUG)
85
86 # Add the log message handler to the logger
87 handler = logging.handlers.RotatingFileHandler(
88 LOG_FILENAME, maxBytes=20, backupCount=5)
89
90 my_logger.addHandler(handler)
91
92 # Log some messages
93 for i in range(20):
94 my_logger.debug('i = %d' % i)
95
96 # See what files are created
97 logfiles = glob.glob('%s*' % LOG_FILENAME)
98
99 for filename in logfiles:
100 print filename
101
102The result should be 6 separate files, each with part of the log history for the
103application::
104
105 /tmp/logging_rotatingfile_example.out
106 /tmp/logging_rotatingfile_example.out.1
107 /tmp/logging_rotatingfile_example.out.2
108 /tmp/logging_rotatingfile_example.out.3
109 /tmp/logging_rotatingfile_example.out.4
110 /tmp/logging_rotatingfile_example.out.5
111
112The most current file is always :file:`/tmp/logging_rotatingfile_example.out`,
113and each time it reaches the size limit it is renamed with the suffix
114``.1``. Each of the existing backup files is renamed to increment the suffix
115(``.1`` becomes ``.2``, etc.) and the ``.5`` file is erased.
116
117Obviously this example sets the log length much much too small as an extreme
118example. You would want to set *maxBytes* to an appropriate value.
119
120Another useful feature of the logging API is the ability to produce different
121messages at different log levels. This allows you to instrument your code with
122debug messages, for example, but turning the log level down so that those debug
123messages are not written for your production system. The default levels are
Vinay Sajipc2211ad2009-01-10 19:22:57 +0000124``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO``, ``DEBUG`` and ``NOTSET``.
Georg Brandlc37f2882007-12-04 17:46:27 +0000125
126The logger, handler, and log message call each specify a level. The log message
127is only emitted if the handler and logger are configured to emit messages of
128that level or lower. For example, if a message is ``CRITICAL``, and the logger
129is set to ``ERROR``, the message is emitted. If a message is a ``WARNING``, and
130the logger is set to produce only ``ERROR``\s, the message is not emitted::
131
132 import logging
133 import sys
134
135 LEVELS = {'debug': logging.DEBUG,
136 'info': logging.INFO,
137 'warning': logging.WARNING,
138 'error': logging.ERROR,
139 'critical': logging.CRITICAL}
140
141 if len(sys.argv) > 1:
142 level_name = sys.argv[1]
143 level = LEVELS.get(level_name, logging.NOTSET)
144 logging.basicConfig(level=level)
145
146 logging.debug('This is a debug message')
147 logging.info('This is an info message')
148 logging.warning('This is a warning message')
149 logging.error('This is an error message')
150 logging.critical('This is a critical error message')
151
152Run the script with an argument like 'debug' or 'warning' to see which messages
153show up at different levels::
154
155 $ python logging_level_example.py debug
156 DEBUG:root:This is a debug message
157 INFO:root:This is an info message
158 WARNING:root:This is a warning message
159 ERROR:root:This is an error message
160 CRITICAL:root:This is a critical error message
161
162 $ python logging_level_example.py info
163 INFO:root:This is an info message
164 WARNING:root:This is a warning message
165 ERROR:root:This is an error message
166 CRITICAL:root:This is a critical error message
167
168You will notice that these log messages all have ``root`` embedded in them. The
169logging module supports a hierarchy of loggers with different names. An easy
170way to tell where a specific log message comes from is to use a separate logger
171object for each of your modules. Each new logger "inherits" the configuration
172of its parent, and log messages sent to a logger include the name of that
173logger. Optionally, each logger can be configured differently, so that messages
174from different modules are handled in different ways. Let's look at a simple
175example of how to log from different modules so it is easy to trace the source
176of the message::
177
178 import logging
179
180 logging.basicConfig(level=logging.WARNING)
181
182 logger1 = logging.getLogger('package1.module1')
183 logger2 = logging.getLogger('package2.module2')
184
185 logger1.warning('This message comes from one module')
186 logger2.warning('And this message comes from another module')
187
188And the output::
189
190 $ python logging_modules_example.py
191 WARNING:package1.module1:This message comes from one module
192 WARNING:package2.module2:And this message comes from another module
193
194There are many more options for configuring logging, including different log
195message formatting options, having messages delivered to multiple destinations,
196and changing the configuration of a long-running application on the fly using a
197socket interface. All of these options are covered in depth in the library
198module documentation.
199
200Loggers
201^^^^^^^
202
203The logging library takes a modular approach and offers the several categories
204of components: loggers, handlers, filters, and formatters. Loggers expose the
205interface that application code directly uses. Handlers send the log records to
206the appropriate destination. Filters provide a finer grained facility for
207determining which log records to send on to a handler. Formatters specify the
208layout of the resultant log record.
209
210:class:`Logger` objects have a threefold job. First, they expose several
211methods to application code so that applications can log messages at runtime.
212Second, logger objects determine which log messages to act upon based upon
213severity (the default filtering facility) or filter objects. Third, logger
214objects pass along relevant log messages to all interested log handlers.
215
216The most widely used methods on logger objects fall into two categories:
217configuration and message sending.
218
219* :meth:`Logger.setLevel` specifies the lowest-severity log message a logger
220 will handle, where debug is the lowest built-in severity level and critical is
221 the highest built-in severity. For example, if the severity level is info,
222 the logger will handle only info, warning, error, and critical messages and
223 will ignore debug messages.
224
225* :meth:`Logger.addFilter` and :meth:`Logger.removeFilter` add and remove filter
226 objects from the logger object. This tutorial does not address filters.
227
228With the logger object configured, the following methods create log messages:
229
230* :meth:`Logger.debug`, :meth:`Logger.info`, :meth:`Logger.warning`,
231 :meth:`Logger.error`, and :meth:`Logger.critical` all create log records with
232 a message and a level that corresponds to their respective method names. The
233 message is actually a format string, which may contain the standard string
234 substitution syntax of :const:`%s`, :const:`%d`, :const:`%f`, and so on. The
235 rest of their arguments is a list of objects that correspond with the
236 substitution fields in the message. With regard to :const:`**kwargs`, the
237 logging methods care only about a keyword of :const:`exc_info` and use it to
238 determine whether to log exception information.
239
240* :meth:`Logger.exception` creates a log message similar to
241 :meth:`Logger.error`. The difference is that :meth:`Logger.exception` dumps a
242 stack trace along with it. Call this method only from an exception handler.
243
244* :meth:`Logger.log` takes a log level as an explicit argument. This is a
245 little more verbose for logging messages than using the log level convenience
246 methods listed above, but this is how to log at custom log levels.
247
Brett Cannon499969a2008-02-25 05:33:07 +0000248:func:`getLogger` returns a reference to a logger instance with the specified
249if it it is provided, or ``root`` if not. The names are period-separated
Georg Brandlc37f2882007-12-04 17:46:27 +0000250hierarchical structures. Multiple calls to :func:`getLogger` with the same name
251will return a reference to the same logger object. Loggers that are further
252down in the hierarchical list are children of loggers higher up in the list.
253For example, given a logger with a name of ``foo``, loggers with names of
254``foo.bar``, ``foo.bar.baz``, and ``foo.bam`` are all children of ``foo``.
255Child loggers propagate messages up to their parent loggers. Because of this,
256it is unnecessary to define and configure all the loggers an application uses.
257It is sufficient to configure a top-level logger and create child loggers as
258needed.
259
260
261Handlers
262^^^^^^^^
263
264:class:`Handler` objects are responsible for dispatching the appropriate log
265messages (based on the log messages' severity) to the handler's specified
266destination. Logger objects can add zero or more handler objects to themselves
267with an :func:`addHandler` method. As an example scenario, an application may
268want to send all log messages to a log file, all log messages of error or higher
269to stdout, and all messages of critical to an email address. This scenario
Georg Brandl907a7202008-02-22 12:31:45 +0000270requires three individual handlers where each handler is responsible for sending
Georg Brandlc37f2882007-12-04 17:46:27 +0000271messages of a specific severity to a specific location.
272
273The standard library includes quite a few handler types; this tutorial uses only
274:class:`StreamHandler` and :class:`FileHandler` in its examples.
275
276There are very few methods in a handler for application developers to concern
277themselves with. The only handler methods that seem relevant for application
278developers who are using the built-in handler objects (that is, not creating
279custom handlers) are the following configuration methods:
280
281* The :meth:`Handler.setLevel` method, just as in logger objects, specifies the
282 lowest severity that will be dispatched to the appropriate destination. Why
283 are there two :func:`setLevel` methods? The level set in the logger
284 determines which severity of messages it will pass to its handlers. The level
285 set in each handler determines which messages that handler will send on.
286 :func:`setFormatter` selects a Formatter object for this handler to use.
287
288* :func:`addFilter` and :func:`removeFilter` respectively configure and
289 deconfigure filter objects on handlers.
290
291Application code should not directly instantiate and use handlers. Instead, the
292:class:`Handler` class is a base class that defines the interface that all
293Handlers should have and establishes some default behavior that child classes
294can use (or override).
295
296
297Formatters
298^^^^^^^^^^
299
300Formatter objects configure the final order, structure, and contents of the log
Brett Cannon499969a2008-02-25 05:33:07 +0000301message. Unlike the base :class:`logging.Handler` class, application code may
Georg Brandlc37f2882007-12-04 17:46:27 +0000302instantiate formatter classes, although you could likely subclass the formatter
303if your application needs special behavior. The constructor takes two optional
304arguments: a message format string and a date format string. If there is no
305message format string, the default is to use the raw message. If there is no
306date format string, the default date format is::
307
308 %Y-%m-%d %H:%M:%S
309
310with the milliseconds tacked on at the end.
311
312The message format string uses ``%(<dictionary key>)s`` styled string
313substitution; the possible keys are documented in :ref:`formatter-objects`.
314
315The following message format string will log the time in a human-readable
316format, the severity of the message, and the contents of the message, in that
317order::
318
319 "%(asctime)s - %(levelname)s - %(message)s"
320
321
322Configuring Logging
323^^^^^^^^^^^^^^^^^^^
324
325Programmers can configure logging either by creating loggers, handlers, and
326formatters explicitly in a main module with the configuration methods listed
327above (using Python code), or by creating a logging config file. The following
328code is an example of configuring a very simple logger, a console handler, and a
329simple formatter in a Python module::
330
331 import logging
332
333 # create logger
334 logger = logging.getLogger("simple_example")
335 logger.setLevel(logging.DEBUG)
336 # create console handler and set level to debug
337 ch = logging.StreamHandler()
338 ch.setLevel(logging.DEBUG)
339 # create formatter
340 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
341 # add formatter to ch
342 ch.setFormatter(formatter)
343 # add ch to logger
344 logger.addHandler(ch)
345
346 # "application" code
347 logger.debug("debug message")
348 logger.info("info message")
349 logger.warn("warn message")
350 logger.error("error message")
351 logger.critical("critical message")
352
353Running this module from the command line produces the following output::
354
355 $ python simple_logging_module.py
356 2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message
357 2005-03-19 15:10:26,620 - simple_example - INFO - info message
358 2005-03-19 15:10:26,695 - simple_example - WARNING - warn message
359 2005-03-19 15:10:26,697 - simple_example - ERROR - error message
360 2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message
361
362The following Python module creates a logger, handler, and formatter nearly
363identical to those in the example listed above, with the only difference being
364the names of the objects::
365
366 import logging
367 import logging.config
368
369 logging.config.fileConfig("logging.conf")
370
371 # create logger
372 logger = logging.getLogger("simpleExample")
373
374 # "application" code
375 logger.debug("debug message")
376 logger.info("info message")
377 logger.warn("warn message")
378 logger.error("error message")
379 logger.critical("critical message")
380
381Here is the logging.conf file::
382
383 [loggers]
384 keys=root,simpleExample
385
386 [handlers]
387 keys=consoleHandler
388
389 [formatters]
390 keys=simpleFormatter
391
392 [logger_root]
393 level=DEBUG
394 handlers=consoleHandler
395
396 [logger_simpleExample]
397 level=DEBUG
398 handlers=consoleHandler
399 qualname=simpleExample
400 propagate=0
401
402 [handler_consoleHandler]
403 class=StreamHandler
404 level=DEBUG
405 formatter=simpleFormatter
406 args=(sys.stdout,)
407
408 [formatter_simpleFormatter]
409 format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
410 datefmt=
411
412The output is nearly identical to that of the non-config-file-based example::
413
414 $ python simple_logging_config.py
415 2005-03-19 15:38:55,977 - simpleExample - DEBUG - debug message
416 2005-03-19 15:38:55,979 - simpleExample - INFO - info message
417 2005-03-19 15:38:56,054 - simpleExample - WARNING - warn message
418 2005-03-19 15:38:56,055 - simpleExample - ERROR - error message
419 2005-03-19 15:38:56,130 - simpleExample - CRITICAL - critical message
420
421You can see that the config file approach has a few advantages over the Python
422code approach, mainly separation of configuration and code and the ability of
423noncoders to easily modify the logging properties.
424
Vinay Sajip99505c82009-01-10 13:38:04 +0000425.. _library-config:
426
Vinay Sajip34bfda52008-09-01 15:08:07 +0000427Configuring Logging for a Library
428^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
429
430When developing a library which uses logging, some consideration needs to be
431given to its configuration. If the using application does not use logging, and
432library code makes logging calls, then a one-off message "No handlers could be
433found for logger X.Y.Z" is printed to the console. This message is intended
434to catch mistakes in logging configuration, but will confuse an application
435developer who is not aware of logging by the library.
436
437In addition to documenting how a library uses logging, a good way to configure
438library logging so that it does not cause a spurious message is to add a
439handler which does nothing. This avoids the message being printed, since a
440handler will be found: it just doesn't produce any output. If the library user
441configures logging for application use, presumably that configuration will add
442some handlers, and if levels are suitably configured then logging calls made
443in library code will send output to those handlers, as normal.
444
445A do-nothing handler can be simply defined as follows::
446
447 import logging
448
449 class NullHandler(logging.Handler):
450 def emit(self, record):
451 pass
452
453An instance of this handler should be added to the top-level logger of the
454logging namespace used by the library. If all logging by a library *foo* is
455done using loggers with names matching "foo.x.y", then the code::
456
457 import logging
458
459 h = NullHandler()
460 logging.getLogger("foo").addHandler(h)
461
462should have the desired effect. If an organisation produces a number of
463libraries, then the logger name specified can be "orgname.foo" rather than
464just "foo".
465
Vinay Sajip213faca2008-12-03 23:22:58 +0000466.. versionadded:: 2.7
467
468The :class:`NullHandler` class was not present in previous versions, but is now
469included, so that it need not be defined in library code.
470
471
Georg Brandlc37f2882007-12-04 17:46:27 +0000472
473Logging Levels
474--------------
475
Georg Brandl8ec7f652007-08-15 14:28:01 +0000476The numeric values of logging levels are given in the following table. These are
477primarily of interest if you want to define your own levels, and need them to
478have specific values relative to the predefined levels. If you define a level
479with the same numeric value, it overwrites the predefined value; the predefined
480name is lost.
481
482+--------------+---------------+
483| Level | Numeric value |
484+==============+===============+
485| ``CRITICAL`` | 50 |
486+--------------+---------------+
487| ``ERROR`` | 40 |
488+--------------+---------------+
489| ``WARNING`` | 30 |
490+--------------+---------------+
491| ``INFO`` | 20 |
492+--------------+---------------+
493| ``DEBUG`` | 10 |
494+--------------+---------------+
495| ``NOTSET`` | 0 |
496+--------------+---------------+
497
498Levels can also be associated with loggers, being set either by the developer or
499through loading a saved logging configuration. When a logging method is called
500on a logger, the logger compares its own level with the level associated with
501the method call. If the logger's level is higher than the method call's, no
502logging message is actually generated. This is the basic mechanism controlling
503the verbosity of logging output.
504
505Logging messages are encoded as instances of the :class:`LogRecord` class. When
506a logger decides to actually log an event, a :class:`LogRecord` instance is
507created from the logging message.
508
509Logging messages are subjected to a dispatch mechanism through the use of
510:dfn:`handlers`, which are instances of subclasses of the :class:`Handler`
511class. Handlers are responsible for ensuring that a logged message (in the form
512of a :class:`LogRecord`) ends up in a particular location (or set of locations)
513which is useful for the target audience for that message (such as end users,
514support desk staff, system administrators, developers). Handlers are passed
515:class:`LogRecord` instances intended for particular destinations. Each logger
516can have zero, one or more handlers associated with it (via the
517:meth:`addHandler` method of :class:`Logger`). In addition to any handlers
518directly associated with a logger, *all handlers associated with all ancestors
519of the logger* are called to dispatch the message.
520
521Just as for loggers, handlers can have levels associated with them. A handler's
522level acts as a filter in the same way as a logger's level does. If a handler
523decides to actually dispatch an event, the :meth:`emit` method is used to send
524the message to its destination. Most user-defined subclasses of :class:`Handler`
525will need to override this :meth:`emit`.
526
Vinay Sajipb5902e62009-01-15 22:48:13 +0000527Useful Handlers
528---------------
529
Georg Brandl8ec7f652007-08-15 14:28:01 +0000530In addition to the base :class:`Handler` class, many useful subclasses are
531provided:
532
533#. :class:`StreamHandler` instances send error messages to streams (file-like
534 objects).
535
536#. :class:`FileHandler` instances send error messages to disk files.
537
Vinay Sajipb5902e62009-01-15 22:48:13 +0000538#. :class:`BaseRotatingHandler` is the base class for handlers that
Vinay Sajip99234c52009-01-12 20:36:18 +0000539 rotate log files at a certain point. It is not meant to be instantiated
540 directly. Instead, use :class:`RotatingFileHandler` or
541 :class:`TimedRotatingFileHandler`.
Vinay Sajipc2211ad2009-01-10 19:22:57 +0000542
Vinay Sajipb5902e62009-01-15 22:48:13 +0000543#. :class:`RotatingFileHandler` instances send error messages to disk
544 files, with support for maximum log file sizes and log file rotation.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000545
Vinay Sajipb5902e62009-01-15 22:48:13 +0000546#. :class:`TimedRotatingFileHandler` instances send error messages to
547 disk files, rotating the log file at certain timed intervals.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000548
Vinay Sajipb5902e62009-01-15 22:48:13 +0000549#. :class:`SocketHandler` instances send error messages to TCP/IP
550 sockets.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000551
Vinay Sajipb5902e62009-01-15 22:48:13 +0000552#. :class:`DatagramHandler` instances send error messages to UDP
553 sockets.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000554
Vinay Sajipb5902e62009-01-15 22:48:13 +0000555#. :class:`SMTPHandler` instances send error messages to a designated
556 email address.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000557
Vinay Sajipb5902e62009-01-15 22:48:13 +0000558#. :class:`SysLogHandler` instances send error messages to a Unix
559 syslog daemon, possibly on a remote machine.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000560
Vinay Sajipb5902e62009-01-15 22:48:13 +0000561#. :class:`NTEventLogHandler` instances send error messages to a
562 Windows NT/2000/XP event log.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000563
Vinay Sajipb5902e62009-01-15 22:48:13 +0000564#. :class:`MemoryHandler` instances send error messages to a buffer
565 in memory, which is flushed whenever specific criteria are met.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000566
Vinay Sajipb5902e62009-01-15 22:48:13 +0000567#. :class:`HTTPHandler` instances send error messages to an HTTP
568 server using either ``GET`` or ``POST`` semantics.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000569
Vinay Sajipb5902e62009-01-15 22:48:13 +0000570#. :class:`WatchedFileHandler` instances watch the file they are
571 logging to. If the file changes, it is closed and reopened using the file
572 name. This handler is only useful on Unix-like systems; Windows does not
573 support the underlying mechanism used.
Vinay Sajipc2211ad2009-01-10 19:22:57 +0000574
Vinay Sajip213faca2008-12-03 23:22:58 +0000575#. :class:`NullHandler` instances do nothing with error messages. They are used
576 by library developers who want to use logging, but want to avoid the "No
577 handlers could be found for logger XXX" message which can be displayed if
Vinay Sajip99505c82009-01-10 13:38:04 +0000578 the library user has not configured logging. See :ref:`library-config` for
579 more information.
Vinay Sajip213faca2008-12-03 23:22:58 +0000580
581.. versionadded:: 2.7
582
583The :class:`NullHandler` class was not present in previous versions.
584
Vinay Sajip7cc97552008-12-30 07:01:25 +0000585The :class:`NullHandler`, :class:`StreamHandler` and :class:`FileHandler`
586classes are defined in the core logging package. The other handlers are
587defined in a sub- module, :mod:`logging.handlers`. (There is also another
588sub-module, :mod:`logging.config`, for configuration functionality.)
Georg Brandl8ec7f652007-08-15 14:28:01 +0000589
590Logged messages are formatted for presentation through instances of the
591:class:`Formatter` class. They are initialized with a format string suitable for
592use with the % operator and a dictionary.
593
594For formatting multiple messages in a batch, instances of
595:class:`BufferingFormatter` can be used. In addition to the format string (which
596is applied to each message in the batch), there is provision for header and
597trailer format strings.
598
599When filtering based on logger level and/or handler level is not enough,
600instances of :class:`Filter` can be added to both :class:`Logger` and
601:class:`Handler` instances (through their :meth:`addFilter` method). Before
602deciding to process a message further, both loggers and handlers consult all
603their filters for permission. If any filter returns a false value, the message
604is not processed further.
605
606The basic :class:`Filter` functionality allows filtering by specific logger
607name. If this feature is used, messages sent to the named logger and its
608children are allowed through the filter, and all others dropped.
609
Vinay Sajipb5902e62009-01-15 22:48:13 +0000610Module-Level Functions
611----------------------
612
Georg Brandl8ec7f652007-08-15 14:28:01 +0000613In addition to the classes described above, there are a number of module- level
614functions.
615
616
617.. function:: getLogger([name])
618
619 Return a logger with the specified name or, if no name is specified, return a
620 logger which is the root logger of the hierarchy. If specified, the name is
621 typically a dot-separated hierarchical name like *"a"*, *"a.b"* or *"a.b.c.d"*.
622 Choice of these names is entirely up to the developer who is using logging.
623
624 All calls to this function with a given name return the same logger instance.
625 This means that logger instances never need to be passed between different parts
626 of an application.
627
628
629.. function:: getLoggerClass()
630
631 Return either the standard :class:`Logger` class, or the last class passed to
632 :func:`setLoggerClass`. This function may be called from within a new class
633 definition, to ensure that installing a customised :class:`Logger` class will
634 not undo customisations already applied by other code. For example::
635
636 class MyLogger(logging.getLoggerClass()):
637 # ... override behaviour here
638
639
640.. function:: debug(msg[, *args[, **kwargs]])
641
642 Logs a message with level :const:`DEBUG` on the root logger. The *msg* is the
643 message format string, and the *args* are the arguments which are merged into
644 *msg* using the string formatting operator. (Note that this means that you can
645 use keywords in the format string, together with a single dictionary argument.)
646
647 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
648 which, if it does not evaluate as false, causes exception information to be
649 added to the logging message. If an exception tuple (in the format returned by
650 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
651 is called to get the exception information.
652
653 The other optional keyword argument is *extra* which can be used to pass a
654 dictionary which is used to populate the __dict__ of the LogRecord created for
655 the logging event with user-defined attributes. These custom attributes can then
656 be used as you like. For example, they could be incorporated into logged
657 messages. For example::
658
659 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
660 logging.basicConfig(format=FORMAT)
661 d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
662 logging.warning("Protocol problem: %s", "connection reset", extra=d)
663
664 would print something like ::
665
666 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
667
668 The keys in the dictionary passed in *extra* should not clash with the keys used
669 by the logging system. (See the :class:`Formatter` documentation for more
670 information on which keys are used by the logging system.)
671
672 If you choose to use these attributes in logged messages, you need to exercise
673 some care. In the above example, for instance, the :class:`Formatter` has been
674 set up with a format string which expects 'clientip' and 'user' in the attribute
675 dictionary of the LogRecord. If these are missing, the message will not be
676 logged because a string formatting exception will occur. So in this case, you
677 always need to pass the *extra* dictionary with these keys.
678
679 While this might be annoying, this feature is intended for use in specialized
680 circumstances, such as multi-threaded servers where the same code executes in
681 many contexts, and interesting conditions which arise are dependent on this
682 context (such as remote client IP address and authenticated user name, in the
683 above example). In such circumstances, it is likely that specialized
684 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
685
686 .. versionchanged:: 2.5
687 *extra* was added.
688
689
690.. function:: info(msg[, *args[, **kwargs]])
691
692 Logs a message with level :const:`INFO` on the root logger. The arguments are
693 interpreted as for :func:`debug`.
694
695
696.. function:: warning(msg[, *args[, **kwargs]])
697
698 Logs a message with level :const:`WARNING` on the root logger. The arguments are
699 interpreted as for :func:`debug`.
700
701
702.. function:: error(msg[, *args[, **kwargs]])
703
704 Logs a message with level :const:`ERROR` on the root logger. The arguments are
705 interpreted as for :func:`debug`.
706
707
708.. function:: critical(msg[, *args[, **kwargs]])
709
710 Logs a message with level :const:`CRITICAL` on the root logger. The arguments
711 are interpreted as for :func:`debug`.
712
713
714.. function:: exception(msg[, *args])
715
716 Logs a message with level :const:`ERROR` on the root logger. The arguments are
717 interpreted as for :func:`debug`. Exception info is added to the logging
718 message. This function should only be called from an exception handler.
719
720
721.. function:: log(level, msg[, *args[, **kwargs]])
722
723 Logs a message with level *level* on the root logger. The other arguments are
724 interpreted as for :func:`debug`.
725
726
727.. function:: disable(lvl)
728
729 Provides an overriding level *lvl* for all loggers which takes precedence over
730 the logger's own level. When the need arises to temporarily throttle logging
731 output down across the whole application, this function can be useful.
732
733
734.. function:: addLevelName(lvl, levelName)
735
736 Associates level *lvl* with text *levelName* in an internal dictionary, which is
737 used to map numeric levels to a textual representation, for example when a
738 :class:`Formatter` formats a message. This function can also be used to define
739 your own levels. The only constraints are that all levels used must be
740 registered using this function, levels should be positive integers and they
741 should increase in increasing order of severity.
742
743
744.. function:: getLevelName(lvl)
745
746 Returns the textual representation of logging level *lvl*. If the level is one
747 of the predefined levels :const:`CRITICAL`, :const:`ERROR`, :const:`WARNING`,
748 :const:`INFO` or :const:`DEBUG` then you get the corresponding string. If you
749 have associated levels with names using :func:`addLevelName` then the name you
750 have associated with *lvl* is returned. If a numeric value corresponding to one
751 of the defined levels is passed in, the corresponding string representation is
752 returned. Otherwise, the string "Level %s" % lvl is returned.
753
754
755.. function:: makeLogRecord(attrdict)
756
757 Creates and returns a new :class:`LogRecord` instance whose attributes are
758 defined by *attrdict*. This function is useful for taking a pickled
759 :class:`LogRecord` attribute dictionary, sent over a socket, and reconstituting
760 it as a :class:`LogRecord` instance at the receiving end.
761
762
763.. function:: basicConfig([**kwargs])
764
765 Does basic configuration for the logging system by creating a
766 :class:`StreamHandler` with a default :class:`Formatter` and adding it to the
Vinay Sajipe28fa292008-01-07 15:30:36 +0000767 root logger. The function does nothing if any handlers have been defined for
768 the root logger. The functions :func:`debug`, :func:`info`, :func:`warning`,
Georg Brandl8ec7f652007-08-15 14:28:01 +0000769 :func:`error` and :func:`critical` will call :func:`basicConfig` automatically
770 if no handlers are defined for the root logger.
771
Georg Brandldfb5bbd2008-05-09 06:18:27 +0000772 This function does nothing if the root logger already has handlers configured.
773
Georg Brandl8ec7f652007-08-15 14:28:01 +0000774 .. versionchanged:: 2.4
775 Formerly, :func:`basicConfig` did not take any keyword arguments.
776
777 The following keyword arguments are supported.
778
779 +--------------+---------------------------------------------+
780 | Format | Description |
781 +==============+=============================================+
782 | ``filename`` | Specifies that a FileHandler be created, |
783 | | using the specified filename, rather than a |
784 | | StreamHandler. |
785 +--------------+---------------------------------------------+
786 | ``filemode`` | Specifies the mode to open the file, if |
787 | | filename is specified (if filemode is |
788 | | unspecified, it defaults to 'a'). |
789 +--------------+---------------------------------------------+
790 | ``format`` | Use the specified format string for the |
791 | | handler. |
792 +--------------+---------------------------------------------+
793 | ``datefmt`` | Use the specified date/time format. |
794 +--------------+---------------------------------------------+
795 | ``level`` | Set the root logger level to the specified |
796 | | level. |
797 +--------------+---------------------------------------------+
798 | ``stream`` | Use the specified stream to initialize the |
799 | | StreamHandler. Note that this argument is |
800 | | incompatible with 'filename' - if both are |
801 | | present, 'stream' is ignored. |
802 +--------------+---------------------------------------------+
803
804
805.. function:: shutdown()
806
807 Informs the logging system to perform an orderly shutdown by flushing and
Vinay Sajip91f0ee42008-03-16 21:35:58 +0000808 closing all handlers. This should be called at application exit and no
809 further use of the logging system should be made after this call.
Georg Brandl8ec7f652007-08-15 14:28:01 +0000810
811
812.. function:: setLoggerClass(klass)
813
814 Tells the logging system to use the class *klass* when instantiating a logger.
815 The class should define :meth:`__init__` such that only a name argument is
816 required, and the :meth:`__init__` should call :meth:`Logger.__init__`. This
817 function is typically called before any loggers are instantiated by applications
818 which need to use custom logger behavior.
819
820
821.. seealso::
822
823 :pep:`282` - A Logging System
824 The proposal which described this feature for inclusion in the Python standard
825 library.
826
Georg Brandl2b92f6b2007-12-06 01:52:24 +0000827 `Original Python logging package <http://www.red-dove.com/python_logging.html>`_
Georg Brandl8ec7f652007-08-15 14:28:01 +0000828 This is the original source for the :mod:`logging` package. The version of the
829 package available from this site is suitable for use with Python 1.5.2, 2.1.x
830 and 2.2.x, which do not include the :mod:`logging` package in the standard
831 library.
832
833
834Logger Objects
835--------------
836
837Loggers have the following attributes and methods. Note that Loggers are never
838instantiated directly, but always through the module-level function
839``logging.getLogger(name)``.
840
841
842.. attribute:: Logger.propagate
843
844 If this evaluates to false, logging messages are not passed by this logger or by
845 child loggers to higher level (ancestor) loggers. The constructor sets this
846 attribute to 1.
847
848
849.. method:: Logger.setLevel(lvl)
850
851 Sets the threshold for this logger to *lvl*. Logging messages which are less
852 severe than *lvl* will be ignored. When a logger is created, the level is set to
853 :const:`NOTSET` (which causes all messages to be processed when the logger is
854 the root logger, or delegation to the parent when the logger is a non-root
855 logger). Note that the root logger is created with level :const:`WARNING`.
856
857 The term "delegation to the parent" means that if a logger has a level of
858 NOTSET, its chain of ancestor loggers is traversed until either an ancestor with
859 a level other than NOTSET is found, or the root is reached.
860
861 If an ancestor is found with a level other than NOTSET, then that ancestor's
862 level is treated as the effective level of the logger where the ancestor search
863 began, and is used to determine how a logging event is handled.
864
865 If the root is reached, and it has a level of NOTSET, then all messages will be
866 processed. Otherwise, the root's level will be used as the effective level.
867
868
869.. method:: Logger.isEnabledFor(lvl)
870
871 Indicates if a message of severity *lvl* would be processed by this logger.
872 This method checks first the module-level level set by
873 ``logging.disable(lvl)`` and then the logger's effective level as determined
874 by :meth:`getEffectiveLevel`.
875
876
877.. method:: Logger.getEffectiveLevel()
878
879 Indicates the effective level for this logger. If a value other than
880 :const:`NOTSET` has been set using :meth:`setLevel`, it is returned. Otherwise,
881 the hierarchy is traversed towards the root until a value other than
882 :const:`NOTSET` is found, and that value is returned.
883
884
885.. method:: Logger.debug(msg[, *args[, **kwargs]])
886
887 Logs a message with level :const:`DEBUG` on this logger. The *msg* is the
888 message format string, and the *args* are the arguments which are merged into
889 *msg* using the string formatting operator. (Note that this means that you can
890 use keywords in the format string, together with a single dictionary argument.)
891
892 There are two keyword arguments in *kwargs* which are inspected: *exc_info*
893 which, if it does not evaluate as false, causes exception information to be
894 added to the logging message. If an exception tuple (in the format returned by
895 :func:`sys.exc_info`) is provided, it is used; otherwise, :func:`sys.exc_info`
896 is called to get the exception information.
897
898 The other optional keyword argument is *extra* which can be used to pass a
899 dictionary which is used to populate the __dict__ of the LogRecord created for
900 the logging event with user-defined attributes. These custom attributes can then
901 be used as you like. For example, they could be incorporated into logged
902 messages. For example::
903
904 FORMAT = "%(asctime)-15s %(clientip)s %(user)-8s %(message)s"
905 logging.basicConfig(format=FORMAT)
Neal Norwitz53004282007-10-23 05:44:27 +0000906 d = { 'clientip' : '192.168.0.1', 'user' : 'fbloggs' }
Georg Brandl8ec7f652007-08-15 14:28:01 +0000907 logger = logging.getLogger("tcpserver")
908 logger.warning("Protocol problem: %s", "connection reset", extra=d)
909
910 would print something like ::
911
912 2006-02-08 22:20:02,165 192.168.0.1 fbloggs Protocol problem: connection reset
913
914 The keys in the dictionary passed in *extra* should not clash with the keys used
915 by the logging system. (See the :class:`Formatter` documentation for more
916 information on which keys are used by the logging system.)
917
918 If you choose to use these attributes in logged messages, you need to exercise
919 some care. In the above example, for instance, the :class:`Formatter` has been
920 set up with a format string which expects 'clientip' and 'user' in the attribute
921 dictionary of the LogRecord. If these are missing, the message will not be
922 logged because a string formatting exception will occur. So in this case, you
923 always need to pass the *extra* dictionary with these keys.
924
925 While this might be annoying, this feature is intended for use in specialized
926 circumstances, such as multi-threaded servers where the same code executes in
927 many contexts, and interesting conditions which arise are dependent on this
928 context (such as remote client IP address and authenticated user name, in the
929 above example). In such circumstances, it is likely that specialized
930 :class:`Formatter`\ s would be used with particular :class:`Handler`\ s.
931
932 .. versionchanged:: 2.5
933 *extra* was added.
934
935
936.. method:: Logger.info(msg[, *args[, **kwargs]])
937
938 Logs a message with level :const:`INFO` on this logger. The arguments are
939 interpreted as for :meth:`debug`.
940
941
942.. method:: Logger.warning(msg[, *args[, **kwargs]])
943
944 Logs a message with level :const:`WARNING` on this logger. The arguments are
945 interpreted as for :meth:`debug`.
946
947
948.. method:: Logger.error(msg[, *args[, **kwargs]])
949
950 Logs a message with level :const:`ERROR` on this logger. The arguments are
951 interpreted as for :meth:`debug`.
952
953
954.. method:: Logger.critical(msg[, *args[, **kwargs]])
955
956 Logs a message with level :const:`CRITICAL` on this logger. The arguments are
957 interpreted as for :meth:`debug`.
958
959
960.. method:: Logger.log(lvl, msg[, *args[, **kwargs]])
961
962 Logs a message with integer level *lvl* on this logger. The other arguments are
963 interpreted as for :meth:`debug`.
964
965
966.. method:: Logger.exception(msg[, *args])
967
968 Logs a message with level :const:`ERROR` on this logger. The arguments are
969 interpreted as for :meth:`debug`. Exception info is added to the logging
970 message. This method should only be called from an exception handler.
971
972
973.. method:: Logger.addFilter(filt)
974
975 Adds the specified filter *filt* to this logger.
976
977
978.. method:: Logger.removeFilter(filt)
979
980 Removes the specified filter *filt* from this logger.
981
982
983.. method:: Logger.filter(record)
984
985 Applies this logger's filters to the record and returns a true value if the
986 record is to be processed.
987
988
989.. method:: Logger.addHandler(hdlr)
990
991 Adds the specified handler *hdlr* to this logger.
992
993
994.. method:: Logger.removeHandler(hdlr)
995
996 Removes the specified handler *hdlr* from this logger.
997
998
999.. method:: Logger.findCaller()
1000
1001 Finds the caller's source filename and line number. Returns the filename, line
1002 number and function name as a 3-element tuple.
1003
Matthias Klosef0e29182007-08-16 12:03:44 +00001004 .. versionchanged:: 2.4
Georg Brandl8ec7f652007-08-15 14:28:01 +00001005 The function name was added. In earlier versions, the filename and line number
1006 were returned as a 2-element tuple..
1007
1008
1009.. method:: Logger.handle(record)
1010
1011 Handles a record by passing it to all handlers associated with this logger and
1012 its ancestors (until a false value of *propagate* is found). This method is used
1013 for unpickled records received from a socket, as well as those created locally.
1014 Logger-level filtering is applied using :meth:`filter`.
1015
1016
1017.. method:: Logger.makeRecord(name, lvl, fn, lno, msg, args, exc_info [, func, extra])
1018
1019 This is a factory method which can be overridden in subclasses to create
1020 specialized :class:`LogRecord` instances.
1021
1022 .. versionchanged:: 2.5
1023 *func* and *extra* were added.
1024
1025
1026.. _minimal-example:
1027
1028Basic example
1029-------------
1030
1031.. versionchanged:: 2.4
1032 formerly :func:`basicConfig` did not take any keyword arguments.
1033
1034The :mod:`logging` package provides a lot of flexibility, and its configuration
1035can appear daunting. This section demonstrates that simple use of the logging
1036package is possible.
1037
1038The simplest example shows logging to the console::
1039
1040 import logging
1041
1042 logging.debug('A debug message')
1043 logging.info('Some information')
1044 logging.warning('A shot across the bows')
1045
1046If you run the above script, you'll see this::
1047
1048 WARNING:root:A shot across the bows
1049
1050Because no particular logger was specified, the system used the root logger. The
1051debug and info messages didn't appear because by default, the root logger is
1052configured to only handle messages with a severity of WARNING or above. The
1053message format is also a configuration default, as is the output destination of
1054the messages - ``sys.stderr``. The severity level, the message format and
1055destination can be easily changed, as shown in the example below::
1056
1057 import logging
1058
1059 logging.basicConfig(level=logging.DEBUG,
1060 format='%(asctime)s %(levelname)s %(message)s',
1061 filename='/tmp/myapp.log',
1062 filemode='w')
1063 logging.debug('A debug message')
1064 logging.info('Some information')
1065 logging.warning('A shot across the bows')
1066
1067The :meth:`basicConfig` method is used to change the configuration defaults,
1068which results in output (written to ``/tmp/myapp.log``) which should look
1069something like the following::
1070
1071 2004-07-02 13:00:08,743 DEBUG A debug message
1072 2004-07-02 13:00:08,743 INFO Some information
1073 2004-07-02 13:00:08,743 WARNING A shot across the bows
1074
1075This time, all messages with a severity of DEBUG or above were handled, and the
1076format of the messages was also changed, and output went to the specified file
1077rather than the console.
1078
1079Formatting uses standard Python string formatting - see section
1080:ref:`string-formatting`. The format string takes the following common
1081specifiers. For a complete list of specifiers, consult the :class:`Formatter`
1082documentation.
1083
1084+-------------------+-----------------------------------------------+
1085| Format | Description |
1086+===================+===============================================+
1087| ``%(name)s`` | Name of the logger (logging channel). |
1088+-------------------+-----------------------------------------------+
1089| ``%(levelname)s`` | Text logging level for the message |
1090| | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
1091| | ``'ERROR'``, ``'CRITICAL'``). |
1092+-------------------+-----------------------------------------------+
1093| ``%(asctime)s`` | Human-readable time when the |
1094| | :class:`LogRecord` was created. By default |
1095| | this is of the form "2003-07-08 16:49:45,896" |
1096| | (the numbers after the comma are millisecond |
1097| | portion of the time). |
1098+-------------------+-----------------------------------------------+
1099| ``%(message)s`` | The logged message. |
1100+-------------------+-----------------------------------------------+
1101
1102To change the date/time format, you can pass an additional keyword parameter,
1103*datefmt*, as in the following::
1104
1105 import logging
1106
1107 logging.basicConfig(level=logging.DEBUG,
1108 format='%(asctime)s %(levelname)-8s %(message)s',
1109 datefmt='%a, %d %b %Y %H:%M:%S',
1110 filename='/temp/myapp.log',
1111 filemode='w')
1112 logging.debug('A debug message')
1113 logging.info('Some information')
1114 logging.warning('A shot across the bows')
1115
1116which would result in output like ::
1117
1118 Fri, 02 Jul 2004 13:06:18 DEBUG A debug message
1119 Fri, 02 Jul 2004 13:06:18 INFO Some information
1120 Fri, 02 Jul 2004 13:06:18 WARNING A shot across the bows
1121
1122The date format string follows the requirements of :func:`strftime` - see the
1123documentation for the :mod:`time` module.
1124
1125If, instead of sending logging output to the console or a file, you'd rather use
1126a file-like object which you have created separately, you can pass it to
1127:func:`basicConfig` using the *stream* keyword argument. Note that if both
1128*stream* and *filename* keyword arguments are passed, the *stream* argument is
1129ignored.
1130
1131Of course, you can put variable information in your output. To do this, simply
1132have the message be a format string and pass in additional arguments containing
1133the variable information, as in the following example::
1134
1135 import logging
1136
1137 logging.basicConfig(level=logging.DEBUG,
1138 format='%(asctime)s %(levelname)-8s %(message)s',
1139 datefmt='%a, %d %b %Y %H:%M:%S',
1140 filename='/temp/myapp.log',
1141 filemode='w')
1142 logging.error('Pack my box with %d dozen %s', 5, 'liquor jugs')
1143
1144which would result in ::
1145
1146 Wed, 21 Jul 2004 15:35:16 ERROR Pack my box with 5 dozen liquor jugs
1147
1148
1149.. _multiple-destinations:
1150
1151Logging to multiple destinations
1152--------------------------------
1153
1154Let's say you want to log to console and file with different message formats and
1155in differing circumstances. Say you want to log messages with levels of DEBUG
1156and higher to file, and those messages at level INFO and higher to the console.
1157Let's also assume that the file should contain timestamps, but the console
1158messages should not. Here's how you can achieve this::
1159
1160 import logging
1161
1162 # set up logging to file - see previous section for more details
1163 logging.basicConfig(level=logging.DEBUG,
1164 format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
1165 datefmt='%m-%d %H:%M',
1166 filename='/temp/myapp.log',
1167 filemode='w')
1168 # define a Handler which writes INFO messages or higher to the sys.stderr
1169 console = logging.StreamHandler()
1170 console.setLevel(logging.INFO)
1171 # set a format which is simpler for console use
1172 formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
1173 # tell the handler to use this format
1174 console.setFormatter(formatter)
1175 # add the handler to the root logger
1176 logging.getLogger('').addHandler(console)
1177
1178 # Now, we can log to the root logger, or any other logger. First the root...
1179 logging.info('Jackdaws love my big sphinx of quartz.')
1180
1181 # Now, define a couple of other loggers which might represent areas in your
1182 # application:
1183
1184 logger1 = logging.getLogger('myapp.area1')
1185 logger2 = logging.getLogger('myapp.area2')
1186
1187 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1188 logger1.info('How quickly daft jumping zebras vex.')
1189 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1190 logger2.error('The five boxing wizards jump quickly.')
1191
1192When you run this, on the console you will see ::
1193
1194 root : INFO Jackdaws love my big sphinx of quartz.
1195 myapp.area1 : INFO How quickly daft jumping zebras vex.
1196 myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
1197 myapp.area2 : ERROR The five boxing wizards jump quickly.
1198
1199and in the file you will see something like ::
1200
1201 10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
1202 10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1203 10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
1204 10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1205 10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
1206
1207As you can see, the DEBUG message only shows up in the file. The other messages
1208are sent to both destinations.
1209
1210This example uses console and file handlers, but you can use any number and
1211combination of handlers you choose.
1212
1213
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001214.. _context-info:
1215
1216Adding contextual information to your logging output
1217----------------------------------------------------
1218
1219Sometimes you want logging output to contain contextual information in
1220addition to the parameters passed to the logging call. For example, in a
1221networked application, it may be desirable to log client-specific information
1222in the log (e.g. remote client's username, or IP address). Although you could
1223use the *extra* parameter to achieve this, it's not always convenient to pass
1224the information in this way. While it might be tempting to create
1225:class:`Logger` instances on a per-connection basis, this is not a good idea
1226because these instances are not garbage collected. While this is not a problem
1227in practice, when the number of :class:`Logger` instances is dependent on the
1228level of granularity you want to use in logging an application, it could
1229be hard to manage if the number of :class:`Logger` instances becomes
1230effectively unbounded.
1231
Vinay Sajipc7403352008-01-18 15:54:14 +00001232An easy way in which you can pass contextual information to be output along
1233with logging event information is to use the :class:`LoggerAdapter` class.
1234This class is designed to look like a :class:`Logger`, so that you can call
1235:meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
1236:meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
1237same signatures as their counterparts in :class:`Logger`, so you can use the
1238two types of instances interchangeably.
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001239
Vinay Sajipc7403352008-01-18 15:54:14 +00001240When you create an instance of :class:`LoggerAdapter`, you pass it a
1241:class:`Logger` instance and a dict-like object which contains your contextual
1242information. When you call one of the logging methods on an instance of
1243:class:`LoggerAdapter`, it delegates the call to the underlying instance of
1244:class:`Logger` passed to its constructor, and arranges to pass the contextual
1245information in the delegated call. Here's a snippet from the code of
1246:class:`LoggerAdapter`::
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001247
Vinay Sajipc7403352008-01-18 15:54:14 +00001248 def debug(self, msg, *args, **kwargs):
1249 """
1250 Delegate a debug call to the underlying logger, after adding
1251 contextual information from this adapter instance.
1252 """
1253 msg, kwargs = self.process(msg, kwargs)
1254 self.logger.debug(msg, *args, **kwargs)
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001255
Vinay Sajipc7403352008-01-18 15:54:14 +00001256The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
1257information is added to the logging output. It's passed the message and
1258keyword arguments of the logging call, and it passes back (potentially)
1259modified versions of these to use in the call to the underlying logger. The
1260default implementation of this method leaves the message alone, but inserts
1261an "extra" key in the keyword argument whose value is the dict-like object
1262passed to the constructor. Of course, if you had passed an "extra" keyword
1263argument in the call to the adapter, it will be silently overwritten.
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001264
Vinay Sajipc7403352008-01-18 15:54:14 +00001265The advantage of using "extra" is that the values in the dict-like object are
1266merged into the :class:`LogRecord` instance's __dict__, allowing you to use
1267customized strings with your :class:`Formatter` instances which know about
1268the keys of the dict-like object. If you need a different method, e.g. if you
1269want to prepend or append the contextual information to the message string,
1270you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
1271to do what you need. Here's an example script which uses this class, which
1272also illustrates what dict-like behaviour is needed from an arbitrary
1273"dict-like" object for use in the constructor::
1274
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001275 import logging
Vinay Sajip733024a2008-01-21 17:39:22 +00001276
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001277 class ConnInfo:
1278 """
1279 An example class which shows how an arbitrary class can be used as
1280 the 'extra' context information repository passed to a LoggerAdapter.
1281 """
Vinay Sajip733024a2008-01-21 17:39:22 +00001282
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001283 def __getitem__(self, name):
1284 """
1285 To allow this instance to look like a dict.
1286 """
1287 from random import choice
1288 if name == "ip":
1289 result = choice(["127.0.0.1", "192.168.0.1"])
1290 elif name == "user":
1291 result = choice(["jim", "fred", "sheila"])
1292 else:
1293 result = self.__dict__.get(name, "?")
1294 return result
Vinay Sajip733024a2008-01-21 17:39:22 +00001295
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001296 def __iter__(self):
1297 """
1298 To allow iteration over keys, which will be merged into
1299 the LogRecord dict before formatting and output.
1300 """
1301 keys = ["ip", "user"]
1302 keys.extend(self.__dict__.keys())
1303 return keys.__iter__()
Vinay Sajip733024a2008-01-21 17:39:22 +00001304
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001305 if __name__ == "__main__":
1306 from random import choice
1307 levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
1308 a1 = logging.LoggerAdapter(logging.getLogger("a.b.c"),
1309 { "ip" : "123.231.231.123", "user" : "sheila" })
1310 logging.basicConfig(level=logging.DEBUG,
1311 format="%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s")
1312 a1.debug("A debug message")
1313 a1.info("An info message with %s", "some parameters")
1314 a2 = logging.LoggerAdapter(logging.getLogger("d.e.f"), ConnInfo())
1315 for x in range(10):
1316 lvl = choice(levels)
1317 lvlname = logging.getLevelName(lvl)
1318 a2.log(lvl, "A message at %s level with %d %s", lvlname, 2, "parameters")
Vinay Sajipc7403352008-01-18 15:54:14 +00001319
1320When this script is run, the output should look something like this::
1321
Georg Brandlf8e6afb2008-01-19 10:11:27 +00001322 2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
1323 2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
1324 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
1325 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
1326 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
1327 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
1328 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
1329 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
1330 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
1331 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
1332 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
1333 2008-01-18 14:49:54,033 d.e.f WARNING IP: 127.0.0.1 User: jim A message at WARNING level with 2 parameters
Vinay Sajipc7403352008-01-18 15:54:14 +00001334
1335.. versionadded:: 2.6
1336
1337The :class:`LoggerAdapter` class was not present in previous versions.
1338
Vinay Sajipaa0665b2008-01-07 19:40:10 +00001339
Georg Brandl8ec7f652007-08-15 14:28:01 +00001340.. _network-logging:
1341
1342Sending and receiving logging events across a network
1343-----------------------------------------------------
1344
1345Let's say you want to send logging events across a network, and handle them at
1346the receiving end. A simple way of doing this is attaching a
1347:class:`SocketHandler` instance to the root logger at the sending end::
1348
1349 import logging, logging.handlers
1350
1351 rootLogger = logging.getLogger('')
1352 rootLogger.setLevel(logging.DEBUG)
1353 socketHandler = logging.handlers.SocketHandler('localhost',
1354 logging.handlers.DEFAULT_TCP_LOGGING_PORT)
1355 # don't bother with a formatter, since a socket handler sends the event as
1356 # an unformatted pickle
1357 rootLogger.addHandler(socketHandler)
1358
1359 # Now, we can log to the root logger, or any other logger. First the root...
1360 logging.info('Jackdaws love my big sphinx of quartz.')
1361
1362 # Now, define a couple of other loggers which might represent areas in your
1363 # application:
1364
1365 logger1 = logging.getLogger('myapp.area1')
1366 logger2 = logging.getLogger('myapp.area2')
1367
1368 logger1.debug('Quick zephyrs blow, vexing daft Jim.')
1369 logger1.info('How quickly daft jumping zebras vex.')
1370 logger2.warning('Jail zesty vixen who grabbed pay from quack.')
1371 logger2.error('The five boxing wizards jump quickly.')
1372
Georg Brandle152a772008-05-24 18:31:28 +00001373At the receiving end, you can set up a receiver using the :mod:`SocketServer`
Georg Brandl8ec7f652007-08-15 14:28:01 +00001374module. Here is a basic working example::
1375
1376 import cPickle
1377 import logging
1378 import logging.handlers
Georg Brandle152a772008-05-24 18:31:28 +00001379 import SocketServer
Georg Brandl8ec7f652007-08-15 14:28:01 +00001380 import struct
1381
1382
Georg Brandle152a772008-05-24 18:31:28 +00001383 class LogRecordStreamHandler(SocketServer.StreamRequestHandler):
Georg Brandl8ec7f652007-08-15 14:28:01 +00001384 """Handler for a streaming logging request.
1385
1386 This basically logs the record using whatever logging policy is
1387 configured locally.
1388 """
1389
1390 def handle(self):
1391 """
1392 Handle multiple requests - each expected to be a 4-byte length,
1393 followed by the LogRecord in pickle format. Logs the record
1394 according to whatever policy is configured locally.
1395 """
1396 while 1:
1397 chunk = self.connection.recv(4)
1398 if len(chunk) < 4:
1399 break
1400 slen = struct.unpack(">L", chunk)[0]
1401 chunk = self.connection.recv(slen)
1402 while len(chunk) < slen:
1403 chunk = chunk + self.connection.recv(slen - len(chunk))
1404 obj = self.unPickle(chunk)
1405 record = logging.makeLogRecord(obj)
1406 self.handleLogRecord(record)
1407
1408 def unPickle(self, data):
1409 return cPickle.loads(data)
1410
1411 def handleLogRecord(self, record):
1412 # if a name is specified, we use the named logger rather than the one
1413 # implied by the record.
1414 if self.server.logname is not None:
1415 name = self.server.logname
1416 else:
1417 name = record.name
1418 logger = logging.getLogger(name)
1419 # N.B. EVERY record gets logged. This is because Logger.handle
1420 # is normally called AFTER logger-level filtering. If you want
1421 # to do filtering, do it at the client end to save wasting
1422 # cycles and network bandwidth!
1423 logger.handle(record)
1424
Georg Brandle152a772008-05-24 18:31:28 +00001425 class LogRecordSocketReceiver(SocketServer.ThreadingTCPServer):
Georg Brandl8ec7f652007-08-15 14:28:01 +00001426 """simple TCP socket-based logging receiver suitable for testing.
1427 """
1428
1429 allow_reuse_address = 1
1430
1431 def __init__(self, host='localhost',
1432 port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
1433 handler=LogRecordStreamHandler):
Georg Brandle152a772008-05-24 18:31:28 +00001434 SocketServer.ThreadingTCPServer.__init__(self, (host, port), handler)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001435 self.abort = 0
1436 self.timeout = 1
1437 self.logname = None
1438
1439 def serve_until_stopped(self):
1440 import select
1441 abort = 0
1442 while not abort:
1443 rd, wr, ex = select.select([self.socket.fileno()],
1444 [], [],
1445 self.timeout)
1446 if rd:
1447 self.handle_request()
1448 abort = self.abort
1449
1450 def main():
1451 logging.basicConfig(
1452 format="%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s")
1453 tcpserver = LogRecordSocketReceiver()
1454 print "About to start TCP server..."
1455 tcpserver.serve_until_stopped()
1456
1457 if __name__ == "__main__":
1458 main()
1459
1460First run the server, and then the client. On the client side, nothing is
1461printed on the console; on the server side, you should see something like::
1462
1463 About to start TCP server...
1464 59 root INFO Jackdaws love my big sphinx of quartz.
1465 59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
1466 69 myapp.area1 INFO How quickly daft jumping zebras vex.
1467 69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
1468 69 myapp.area2 ERROR The five boxing wizards jump quickly.
1469
1470
1471Handler Objects
1472---------------
1473
1474Handlers have the following attributes and methods. Note that :class:`Handler`
1475is never instantiated directly; this class acts as a base for more useful
1476subclasses. However, the :meth:`__init__` method in subclasses needs to call
1477:meth:`Handler.__init__`.
1478
1479
1480.. method:: Handler.__init__(level=NOTSET)
1481
1482 Initializes the :class:`Handler` instance by setting its level, setting the list
1483 of filters to the empty list and creating a lock (using :meth:`createLock`) for
1484 serializing access to an I/O mechanism.
1485
1486
1487.. method:: Handler.createLock()
1488
1489 Initializes a thread lock which can be used to serialize access to underlying
1490 I/O functionality which may not be threadsafe.
1491
1492
1493.. method:: Handler.acquire()
1494
1495 Acquires the thread lock created with :meth:`createLock`.
1496
1497
1498.. method:: Handler.release()
1499
1500 Releases the thread lock acquired with :meth:`acquire`.
1501
1502
1503.. method:: Handler.setLevel(lvl)
1504
1505 Sets the threshold for this handler to *lvl*. Logging messages which are less
1506 severe than *lvl* will be ignored. When a handler is created, the level is set
1507 to :const:`NOTSET` (which causes all messages to be processed).
1508
1509
1510.. method:: Handler.setFormatter(form)
1511
1512 Sets the :class:`Formatter` for this handler to *form*.
1513
1514
1515.. method:: Handler.addFilter(filt)
1516
1517 Adds the specified filter *filt* to this handler.
1518
1519
1520.. method:: Handler.removeFilter(filt)
1521
1522 Removes the specified filter *filt* from this handler.
1523
1524
1525.. method:: Handler.filter(record)
1526
1527 Applies this handler's filters to the record and returns a true value if the
1528 record is to be processed.
1529
1530
1531.. method:: Handler.flush()
1532
1533 Ensure all logging output has been flushed. This version does nothing and is
1534 intended to be implemented by subclasses.
1535
1536
1537.. method:: Handler.close()
1538
Vinay Sajipaa5f8732008-09-01 17:44:14 +00001539 Tidy up any resources used by the handler. This version does no output but
1540 removes the handler from an internal list of handlers which is closed when
1541 :func:`shutdown` is called. Subclasses should ensure that this gets called
1542 from overridden :meth:`close` methods.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001543
1544
1545.. method:: Handler.handle(record)
1546
1547 Conditionally emits the specified logging record, depending on filters which may
1548 have been added to the handler. Wraps the actual emission of the record with
1549 acquisition/release of the I/O thread lock.
1550
1551
1552.. method:: Handler.handleError(record)
1553
1554 This method should be called from handlers when an exception is encountered
1555 during an :meth:`emit` call. By default it does nothing, which means that
1556 exceptions get silently ignored. This is what is mostly wanted for a logging
1557 system - most users will not care about errors in the logging system, they are
1558 more interested in application errors. You could, however, replace this with a
1559 custom handler if you wish. The specified record is the one which was being
1560 processed when the exception occurred.
1561
1562
1563.. method:: Handler.format(record)
1564
1565 Do formatting for a record - if a formatter is set, use it. Otherwise, use the
1566 default formatter for the module.
1567
1568
1569.. method:: Handler.emit(record)
1570
1571 Do whatever it takes to actually log the specified logging record. This version
1572 is intended to be implemented by subclasses and so raises a
1573 :exc:`NotImplementedError`.
1574
1575
1576StreamHandler
1577^^^^^^^^^^^^^
1578
1579The :class:`StreamHandler` class, located in the core :mod:`logging` package,
1580sends logging output to streams such as *sys.stdout*, *sys.stderr* or any
1581file-like object (or, more precisely, any object which supports :meth:`write`
1582and :meth:`flush` methods).
1583
1584
1585.. class:: StreamHandler([strm])
1586
1587 Returns a new instance of the :class:`StreamHandler` class. If *strm* is
1588 specified, the instance will use it for logging output; otherwise, *sys.stderr*
1589 will be used.
1590
1591
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001592 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001593
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001594 If a formatter is specified, it is used to format the record. The record
1595 is then written to the stream with a trailing newline. If exception
1596 information is present, it is formatted using
1597 :func:`traceback.print_exception` and appended to the stream.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001598
1599
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001600 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001601
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001602 Flushes the stream by calling its :meth:`flush` method. Note that the
1603 :meth:`close` method is inherited from :class:`Handler` and so does
Vinay Sajipaa5f8732008-09-01 17:44:14 +00001604 no output, so an explicit :meth:`flush` call may be needed at times.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001605
1606
1607FileHandler
1608^^^^^^^^^^^
1609
1610The :class:`FileHandler` class, located in the core :mod:`logging` package,
1611sends logging output to a disk file. It inherits the output functionality from
1612:class:`StreamHandler`.
1613
1614
Vinay Sajipf38ba782008-01-24 12:38:30 +00001615.. class:: FileHandler(filename[, mode[, encoding[, delay]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001616
1617 Returns a new instance of the :class:`FileHandler` class. The specified file is
1618 opened and used as the stream for logging. If *mode* is not specified,
1619 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
Vinay Sajipf38ba782008-01-24 12:38:30 +00001620 with that encoding. If *delay* is true, then file opening is deferred until the
1621 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001622
1623
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001624 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001625
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001626 Closes the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001627
1628
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001629 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001630
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001631 Outputs the record to the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001632
1633
Vinay Sajip51104862009-01-02 18:53:04 +00001634NullHandler
1635^^^^^^^^^^^
1636
1637.. versionadded:: 2.7
1638
1639The :class:`NullHandler` class, located in the core :mod:`logging` package,
1640does not do any formatting or output. It is essentially a "no-op" handler
1641for use by library developers.
1642
1643
1644.. class:: NullHandler()
1645
1646 Returns a new instance of the :class:`NullHandler` class.
1647
1648
1649 .. method:: emit(record)
1650
1651 This method does nothing.
1652
Vinay Sajip99505c82009-01-10 13:38:04 +00001653See :ref:`library-config` for more information on how to use
1654:class:`NullHandler`.
1655
Georg Brandl8ec7f652007-08-15 14:28:01 +00001656WatchedFileHandler
1657^^^^^^^^^^^^^^^^^^
1658
1659.. versionadded:: 2.6
1660
Vinay Sajip51104862009-01-02 18:53:04 +00001661.. module:: logging.handlers
1662
Georg Brandl8ec7f652007-08-15 14:28:01 +00001663The :class:`WatchedFileHandler` class, located in the :mod:`logging.handlers`
1664module, is a :class:`FileHandler` which watches the file it is logging to. If
1665the file changes, it is closed and reopened using the file name.
1666
1667A file change can happen because of usage of programs such as *newsyslog* and
1668*logrotate* which perform log file rotation. This handler, intended for use
1669under Unix/Linux, watches the file to see if it has changed since the last emit.
1670(A file is deemed to have changed if its device or inode have changed.) If the
1671file has changed, the old file stream is closed, and the file opened to get a
1672new stream.
1673
1674This handler is not appropriate for use under Windows, because under Windows
1675open log files cannot be moved or renamed - logging opens the files with
1676exclusive locks - and so there is no need for such a handler. Furthermore,
1677*ST_INO* is not supported under Windows; :func:`stat` always returns zero for
1678this value.
1679
1680
Vinay Sajipf38ba782008-01-24 12:38:30 +00001681.. class:: WatchedFileHandler(filename[,mode[, encoding[, delay]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001682
1683 Returns a new instance of the :class:`WatchedFileHandler` class. The specified
1684 file is opened and used as the stream for logging. If *mode* is not specified,
1685 :const:`'a'` is used. If *encoding* is not *None*, it is used to open the file
Vinay Sajipf38ba782008-01-24 12:38:30 +00001686 with that encoding. If *delay* is true, then file opening is deferred until the
1687 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001688
1689
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001690 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001691
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001692 Outputs the record to the file, but first checks to see if the file has
1693 changed. If it has, the existing stream is flushed and closed and the
1694 file opened again, before outputting the record to the file.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001695
1696
1697RotatingFileHandler
1698^^^^^^^^^^^^^^^^^^^
1699
1700The :class:`RotatingFileHandler` class, located in the :mod:`logging.handlers`
1701module, supports rotation of disk log files.
1702
1703
Vinay Sajipf38ba782008-01-24 12:38:30 +00001704.. class:: RotatingFileHandler(filename[, mode[, maxBytes[, backupCount[, encoding[, delay]]]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001705
1706 Returns a new instance of the :class:`RotatingFileHandler` class. The specified
1707 file is opened and used as the stream for logging. If *mode* is not specified,
Vinay Sajipf38ba782008-01-24 12:38:30 +00001708 ``'a'`` is used. If *encoding* is not *None*, it is used to open the file
1709 with that encoding. If *delay* is true, then file opening is deferred until the
1710 first call to :meth:`emit`. By default, the file grows indefinitely.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001711
1712 You can use the *maxBytes* and *backupCount* values to allow the file to
1713 :dfn:`rollover` at a predetermined size. When the size is about to be exceeded,
1714 the file is closed and a new file is silently opened for output. Rollover occurs
1715 whenever the current log file is nearly *maxBytes* in length; if *maxBytes* is
1716 zero, rollover never occurs. If *backupCount* is non-zero, the system will save
1717 old log files by appending the extensions ".1", ".2" etc., to the filename. For
1718 example, with a *backupCount* of 5 and a base file name of :file:`app.log`, you
1719 would get :file:`app.log`, :file:`app.log.1`, :file:`app.log.2`, up to
1720 :file:`app.log.5`. The file being written to is always :file:`app.log`. When
1721 this file is filled, it is closed and renamed to :file:`app.log.1`, and if files
1722 :file:`app.log.1`, :file:`app.log.2`, etc. exist, then they are renamed to
1723 :file:`app.log.2`, :file:`app.log.3` etc. respectively.
1724
1725
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001726 .. method:: doRollover()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001727
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001728 Does a rollover, as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001729
1730
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001731 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001732
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001733 Outputs the record to the file, catering for rollover as described
1734 previously.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001735
1736
1737TimedRotatingFileHandler
1738^^^^^^^^^^^^^^^^^^^^^^^^
1739
1740The :class:`TimedRotatingFileHandler` class, located in the
1741:mod:`logging.handlers` module, supports rotation of disk log files at certain
1742timed intervals.
1743
1744
Andrew M. Kuchling6dd8cca2008-06-05 23:33:54 +00001745.. class:: TimedRotatingFileHandler(filename [,when [,interval [,backupCount[, encoding[, delay[, utc]]]]]])
Georg Brandl8ec7f652007-08-15 14:28:01 +00001746
1747 Returns a new instance of the :class:`TimedRotatingFileHandler` class. The
1748 specified file is opened and used as the stream for logging. On rotating it also
1749 sets the filename suffix. Rotating happens based on the product of *when* and
1750 *interval*.
1751
1752 You can use the *when* to specify the type of *interval*. The list of possible
Georg Brandld77554f2008-06-06 07:34:50 +00001753 values is below. Note that they are not case sensitive.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001754
Georg Brandl72780a42008-03-02 13:41:39 +00001755 +----------------+-----------------------+
1756 | Value | Type of interval |
1757 +================+=======================+
1758 | ``'S'`` | Seconds |
1759 +----------------+-----------------------+
1760 | ``'M'`` | Minutes |
1761 +----------------+-----------------------+
1762 | ``'H'`` | Hours |
1763 +----------------+-----------------------+
1764 | ``'D'`` | Days |
1765 +----------------+-----------------------+
1766 | ``'W'`` | Week day (0=Monday) |
1767 +----------------+-----------------------+
1768 | ``'midnight'`` | Roll over at midnight |
1769 +----------------+-----------------------+
Georg Brandl8ec7f652007-08-15 14:28:01 +00001770
Georg Brandle6dab2a2008-03-02 14:15:04 +00001771 The system will save old log files by appending extensions to the filename.
1772 The extensions are date-and-time based, using the strftime format
Vinay Sajip89a01cd2008-04-02 21:17:25 +00001773 ``%Y-%m-%d_%H-%M-%S`` or a leading portion thereof, depending on the
Vinay Sajip2a649f92008-07-18 09:00:35 +00001774 rollover interval.
Georg Brandld77554f2008-06-06 07:34:50 +00001775 If the *utc* argument is true, times in UTC will be used; otherwise
Andrew M. Kuchling6dd8cca2008-06-05 23:33:54 +00001776 local time is used.
1777
1778 If *backupCount* is nonzero, at most *backupCount* files
Vinay Sajip89a01cd2008-04-02 21:17:25 +00001779 will be kept, and if more would be created when rollover occurs, the oldest
1780 one is deleted. The deletion logic uses the interval to determine which
1781 files to delete, so changing the interval may leave old files lying around.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001782
1783
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001784 .. method:: doRollover()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001785
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001786 Does a rollover, as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001787
1788
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001789 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001790
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001791 Outputs the record to the file, catering for rollover as described above.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001792
1793
1794SocketHandler
1795^^^^^^^^^^^^^
1796
1797The :class:`SocketHandler` class, located in the :mod:`logging.handlers` module,
1798sends logging output to a network socket. The base class uses a TCP socket.
1799
1800
1801.. class:: SocketHandler(host, port)
1802
1803 Returns a new instance of the :class:`SocketHandler` class intended to
1804 communicate with a remote machine whose address is given by *host* and *port*.
1805
1806
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001807 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001808
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001809 Closes the socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001810
1811
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001812 .. method:: emit()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001813
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001814 Pickles the record's attribute dictionary and writes it to the socket in
1815 binary format. If there is an error with the socket, silently drops the
1816 packet. If the connection was previously lost, re-establishes the
1817 connection. To unpickle the record at the receiving end into a
1818 :class:`LogRecord`, use the :func:`makeLogRecord` function.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001819
1820
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001821 .. method:: handleError()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001822
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001823 Handles an error which has occurred during :meth:`emit`. The most likely
1824 cause is a lost connection. Closes the socket so that we can retry on the
1825 next event.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001826
1827
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001828 .. method:: makeSocket()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001829
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001830 This is a factory method which allows subclasses to define the precise
1831 type of socket they want. The default implementation creates a TCP socket
1832 (:const:`socket.SOCK_STREAM`).
Georg Brandl8ec7f652007-08-15 14:28:01 +00001833
1834
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001835 .. method:: makePickle(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001836
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001837 Pickles the record's attribute dictionary in binary format with a length
1838 prefix, and returns it ready for transmission across the socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001839
1840
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001841 .. method:: send(packet)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001842
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001843 Send a pickled string *packet* to the socket. This function allows for
1844 partial sends which can happen when the network is busy.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001845
1846
1847DatagramHandler
1848^^^^^^^^^^^^^^^
1849
1850The :class:`DatagramHandler` class, located in the :mod:`logging.handlers`
1851module, inherits from :class:`SocketHandler` to support sending logging messages
1852over UDP sockets.
1853
1854
1855.. class:: DatagramHandler(host, port)
1856
1857 Returns a new instance of the :class:`DatagramHandler` class intended to
1858 communicate with a remote machine whose address is given by *host* and *port*.
1859
1860
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001861 .. method:: emit()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001862
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001863 Pickles the record's attribute dictionary and writes it to the socket in
1864 binary format. If there is an error with the socket, silently drops the
1865 packet. To unpickle the record at the receiving end into a
1866 :class:`LogRecord`, use the :func:`makeLogRecord` function.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001867
1868
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001869 .. method:: makeSocket()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001870
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001871 The factory method of :class:`SocketHandler` is here overridden to create
1872 a UDP socket (:const:`socket.SOCK_DGRAM`).
Georg Brandl8ec7f652007-08-15 14:28:01 +00001873
1874
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001875 .. method:: send(s)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001876
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001877 Send a pickled string to a socket.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001878
1879
1880SysLogHandler
1881^^^^^^^^^^^^^
1882
1883The :class:`SysLogHandler` class, located in the :mod:`logging.handlers` module,
1884supports sending logging messages to a remote or local Unix syslog.
1885
1886
1887.. class:: SysLogHandler([address[, facility]])
1888
1889 Returns a new instance of the :class:`SysLogHandler` class intended to
1890 communicate with a remote Unix machine whose address is given by *address* in
1891 the form of a ``(host, port)`` tuple. If *address* is not specified,
1892 ``('localhost', 514)`` is used. The address is used to open a UDP socket. An
1893 alternative to providing a ``(host, port)`` tuple is providing an address as a
1894 string, for example "/dev/log". In this case, a Unix domain socket is used to
1895 send the message to the syslog. If *facility* is not specified,
1896 :const:`LOG_USER` is used.
1897
1898
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001899 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001900
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001901 Closes the socket to the remote host.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001902
1903
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001904 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001905
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001906 The record is formatted, and then sent to the syslog server. If exception
1907 information is present, it is *not* sent to the server.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001908
1909
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001910 .. method:: encodePriority(facility, priority)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001911
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001912 Encodes the facility and priority into an integer. You can pass in strings
1913 or integers - if strings are passed, internal mapping dictionaries are
1914 used to convert them to integers.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001915
1916
1917NTEventLogHandler
1918^^^^^^^^^^^^^^^^^
1919
1920The :class:`NTEventLogHandler` class, located in the :mod:`logging.handlers`
1921module, supports sending logging messages to a local Windows NT, Windows 2000 or
1922Windows XP event log. Before you can use it, you need Mark Hammond's Win32
1923extensions for Python installed.
1924
1925
1926.. class:: NTEventLogHandler(appname[, dllname[, logtype]])
1927
1928 Returns a new instance of the :class:`NTEventLogHandler` class. The *appname* is
1929 used to define the application name as it appears in the event log. An
1930 appropriate registry entry is created using this name. The *dllname* should give
1931 the fully qualified pathname of a .dll or .exe which contains message
1932 definitions to hold in the log (if not specified, ``'win32service.pyd'`` is used
1933 - this is installed with the Win32 extensions and contains some basic
1934 placeholder message definitions. Note that use of these placeholders will make
1935 your event logs big, as the entire message source is held in the log. If you
1936 want slimmer logs, you have to pass in the name of your own .dll or .exe which
1937 contains the message definitions you want to use in the event log). The
1938 *logtype* is one of ``'Application'``, ``'System'`` or ``'Security'``, and
1939 defaults to ``'Application'``.
1940
1941
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001942 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00001943
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001944 At this point, you can remove the application name from the registry as a
1945 source of event log entries. However, if you do this, you will not be able
1946 to see the events as you intended in the Event Log Viewer - it needs to be
1947 able to access the registry to get the .dll name. The current version does
Vinay Sajipaa5f8732008-09-01 17:44:14 +00001948 not do this.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001949
1950
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001951 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001952
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001953 Determines the message ID, event category and event type, and then logs
1954 the message in the NT event log.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001955
1956
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001957 .. method:: getEventCategory(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001958
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001959 Returns the event category for the record. Override this if you want to
1960 specify your own categories. This version returns 0.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001961
1962
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001963 .. method:: getEventType(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001964
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001965 Returns the event type for the record. Override this if you want to
1966 specify your own types. This version does a mapping using the handler's
1967 typemap attribute, which is set up in :meth:`__init__` to a dictionary
1968 which contains mappings for :const:`DEBUG`, :const:`INFO`,
1969 :const:`WARNING`, :const:`ERROR` and :const:`CRITICAL`. If you are using
1970 your own levels, you will either need to override this method or place a
1971 suitable dictionary in the handler's *typemap* attribute.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001972
1973
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001974 .. method:: getMessageID(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00001975
Benjamin Petersonc7b05922008-04-25 01:29:10 +00001976 Returns the message ID for the record. If you are using your own messages,
1977 you could do this by having the *msg* passed to the logger being an ID
1978 rather than a format string. Then, in here, you could use a dictionary
1979 lookup to get the message ID. This version returns 1, which is the base
1980 message ID in :file:`win32service.pyd`.
Georg Brandl8ec7f652007-08-15 14:28:01 +00001981
1982
1983SMTPHandler
1984^^^^^^^^^^^
1985
1986The :class:`SMTPHandler` class, located in the :mod:`logging.handlers` module,
1987supports sending logging messages to an email address via SMTP.
1988
1989
1990.. class:: SMTPHandler(mailhost, fromaddr, toaddrs, subject[, credentials])
1991
1992 Returns a new instance of the :class:`SMTPHandler` class. The instance is
1993 initialized with the from and to addresses and subject line of the email. The
1994 *toaddrs* should be a list of strings. To specify a non-standard SMTP port, use
1995 the (host, port) tuple format for the *mailhost* argument. If you use a string,
1996 the standard SMTP port is used. If your SMTP server requires authentication, you
1997 can specify a (username, password) tuple for the *credentials* argument.
1998
1999 .. versionchanged:: 2.6
2000 *credentials* was added.
2001
2002
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002003 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002004
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002005 Formats the record and sends it to the specified addressees.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002006
2007
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002008 .. method:: getSubject(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002009
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002010 If you want to specify a subject line which is record-dependent, override
2011 this method.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002012
2013
2014MemoryHandler
2015^^^^^^^^^^^^^
2016
2017The :class:`MemoryHandler` class, located in the :mod:`logging.handlers` module,
2018supports buffering of logging records in memory, periodically flushing them to a
2019:dfn:`target` handler. Flushing occurs whenever the buffer is full, or when an
2020event of a certain severity or greater is seen.
2021
2022:class:`MemoryHandler` is a subclass of the more general
2023:class:`BufferingHandler`, which is an abstract class. This buffers logging
2024records in memory. Whenever each record is added to the buffer, a check is made
2025by calling :meth:`shouldFlush` to see if the buffer should be flushed. If it
2026should, then :meth:`flush` is expected to do the needful.
2027
2028
2029.. class:: BufferingHandler(capacity)
2030
2031 Initializes the handler with a buffer of the specified capacity.
2032
2033
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002034 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002035
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002036 Appends the record to the buffer. If :meth:`shouldFlush` returns true,
2037 calls :meth:`flush` to process the buffer.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002038
2039
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002040 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00002041
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002042 You can override this to implement custom flushing behavior. This version
2043 just zaps the buffer to empty.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002044
2045
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002046 .. method:: shouldFlush(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002047
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002048 Returns true if the buffer is up to capacity. This method can be
2049 overridden to implement custom flushing strategies.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002050
2051
2052.. class:: MemoryHandler(capacity[, flushLevel [, target]])
2053
2054 Returns a new instance of the :class:`MemoryHandler` class. The instance is
2055 initialized with a buffer size of *capacity*. If *flushLevel* is not specified,
2056 :const:`ERROR` is used. If no *target* is specified, the target will need to be
2057 set using :meth:`setTarget` before this handler does anything useful.
2058
2059
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002060 .. method:: close()
Georg Brandl8ec7f652007-08-15 14:28:01 +00002061
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002062 Calls :meth:`flush`, sets the target to :const:`None` and clears the
2063 buffer.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002064
2065
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002066 .. method:: flush()
Georg Brandl8ec7f652007-08-15 14:28:01 +00002067
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002068 For a :class:`MemoryHandler`, flushing means just sending the buffered
2069 records to the target, if there is one. Override if you want different
2070 behavior.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002071
2072
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002073 .. method:: setTarget(target)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002074
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002075 Sets the target handler for this handler.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002076
2077
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002078 .. method:: shouldFlush(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002079
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002080 Checks for buffer full or a record at the *flushLevel* or higher.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002081
2082
2083HTTPHandler
2084^^^^^^^^^^^
2085
2086The :class:`HTTPHandler` class, located in the :mod:`logging.handlers` module,
2087supports sending logging messages to a Web server, using either ``GET`` or
2088``POST`` semantics.
2089
2090
2091.. class:: HTTPHandler(host, url[, method])
2092
2093 Returns a new instance of the :class:`HTTPHandler` class. The instance is
2094 initialized with a host address, url and HTTP method. The *host* can be of the
2095 form ``host:port``, should you need to use a specific port number. If no
2096 *method* is specified, ``GET`` is used.
2097
2098
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002099 .. method:: emit(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002100
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002101 Sends the record to the Web server as an URL-encoded dictionary.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002102
2103
Georg Brandlc37f2882007-12-04 17:46:27 +00002104.. _formatter-objects:
2105
Georg Brandl8ec7f652007-08-15 14:28:01 +00002106Formatter Objects
2107-----------------
2108
Georg Brandl430effb2009-01-01 13:05:13 +00002109.. currentmodule:: logging
2110
Georg Brandl8ec7f652007-08-15 14:28:01 +00002111:class:`Formatter`\ s have the following attributes and methods. They are
2112responsible for converting a :class:`LogRecord` to (usually) a string which can
2113be interpreted by either a human or an external system. The base
2114:class:`Formatter` allows a formatting string to be specified. If none is
2115supplied, the default value of ``'%(message)s'`` is used.
2116
2117A Formatter can be initialized with a format string which makes use of knowledge
2118of the :class:`LogRecord` attributes - such as the default value mentioned above
2119making use of the fact that the user's message and arguments are pre-formatted
2120into a :class:`LogRecord`'s *message* attribute. This format string contains
2121standard python %-style mapping keys. See section :ref:`string-formatting`
2122for more information on string formatting.
2123
2124Currently, the useful mapping keys in a :class:`LogRecord` are:
2125
2126+-------------------------+-----------------------------------------------+
2127| Format | Description |
2128+=========================+===============================================+
2129| ``%(name)s`` | Name of the logger (logging channel). |
2130+-------------------------+-----------------------------------------------+
2131| ``%(levelno)s`` | Numeric logging level for the message |
2132| | (:const:`DEBUG`, :const:`INFO`, |
2133| | :const:`WARNING`, :const:`ERROR`, |
2134| | :const:`CRITICAL`). |
2135+-------------------------+-----------------------------------------------+
2136| ``%(levelname)s`` | Text logging level for the message |
2137| | (``'DEBUG'``, ``'INFO'``, ``'WARNING'``, |
2138| | ``'ERROR'``, ``'CRITICAL'``). |
2139+-------------------------+-----------------------------------------------+
2140| ``%(pathname)s`` | Full pathname of the source file where the |
2141| | logging call was issued (if available). |
2142+-------------------------+-----------------------------------------------+
2143| ``%(filename)s`` | Filename portion of pathname. |
2144+-------------------------+-----------------------------------------------+
2145| ``%(module)s`` | Module (name portion of filename). |
2146+-------------------------+-----------------------------------------------+
2147| ``%(funcName)s`` | Name of function containing the logging call. |
2148+-------------------------+-----------------------------------------------+
2149| ``%(lineno)d`` | Source line number where the logging call was |
2150| | issued (if available). |
2151+-------------------------+-----------------------------------------------+
2152| ``%(created)f`` | Time when the :class:`LogRecord` was created |
2153| | (as returned by :func:`time.time`). |
2154+-------------------------+-----------------------------------------------+
2155| ``%(relativeCreated)d`` | Time in milliseconds when the LogRecord was |
2156| | created, relative to the time the logging |
2157| | module was loaded. |
2158+-------------------------+-----------------------------------------------+
2159| ``%(asctime)s`` | Human-readable time when the |
2160| | :class:`LogRecord` was created. By default |
2161| | this is of the form "2003-07-08 16:49:45,896" |
2162| | (the numbers after the comma are millisecond |
2163| | portion of the time). |
2164+-------------------------+-----------------------------------------------+
2165| ``%(msecs)d`` | Millisecond portion of the time when the |
2166| | :class:`LogRecord` was created. |
2167+-------------------------+-----------------------------------------------+
2168| ``%(thread)d`` | Thread ID (if available). |
2169+-------------------------+-----------------------------------------------+
2170| ``%(threadName)s`` | Thread name (if available). |
2171+-------------------------+-----------------------------------------------+
2172| ``%(process)d`` | Process ID (if available). |
2173+-------------------------+-----------------------------------------------+
2174| ``%(message)s`` | The logged message, computed as ``msg % |
2175| | args``. |
2176+-------------------------+-----------------------------------------------+
2177
2178.. versionchanged:: 2.5
2179 *funcName* was added.
2180
2181
2182.. class:: Formatter([fmt[, datefmt]])
2183
2184 Returns a new instance of the :class:`Formatter` class. The instance is
2185 initialized with a format string for the message as a whole, as well as a format
2186 string for the date/time portion of a message. If no *fmt* is specified,
2187 ``'%(message)s'`` is used. If no *datefmt* is specified, the ISO8601 date format
2188 is used.
2189
2190
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002191 .. method:: format(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002192
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002193 The record's attribute dictionary is used as the operand to a string
2194 formatting operation. Returns the resulting string. Before formatting the
2195 dictionary, a couple of preparatory steps are carried out. The *message*
2196 attribute of the record is computed using *msg* % *args*. If the
2197 formatting string contains ``'(asctime)'``, :meth:`formatTime` is called
2198 to format the event time. If there is exception information, it is
2199 formatted using :meth:`formatException` and appended to the message. Note
2200 that the formatted exception information is cached in attribute
2201 *exc_text*. This is useful because the exception information can be
2202 pickled and sent across the wire, but you should be careful if you have
2203 more than one :class:`Formatter` subclass which customizes the formatting
2204 of exception information. In this case, you will have to clear the cached
2205 value after a formatter has done its formatting, so that the next
2206 formatter to handle the event doesn't use the cached value but
2207 recalculates it afresh.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002208
2209
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002210 .. method:: formatTime(record[, datefmt])
Georg Brandl8ec7f652007-08-15 14:28:01 +00002211
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002212 This method should be called from :meth:`format` by a formatter which
2213 wants to make use of a formatted time. This method can be overridden in
2214 formatters to provide for any specific requirement, but the basic behavior
2215 is as follows: if *datefmt* (a string) is specified, it is used with
2216 :func:`time.strftime` to format the creation time of the
2217 record. Otherwise, the ISO8601 format is used. The resulting string is
2218 returned.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002219
2220
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002221 .. method:: formatException(exc_info)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002222
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002223 Formats the specified exception information (a standard exception tuple as
2224 returned by :func:`sys.exc_info`) as a string. This default implementation
2225 just uses :func:`traceback.print_exception`. The resulting string is
2226 returned.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002227
2228
2229Filter Objects
2230--------------
2231
2232:class:`Filter`\ s can be used by :class:`Handler`\ s and :class:`Logger`\ s for
2233more sophisticated filtering than is provided by levels. The base filter class
2234only allows events which are below a certain point in the logger hierarchy. For
2235example, a filter initialized with "A.B" will allow events logged by loggers
2236"A.B", "A.B.C", "A.B.C.D", "A.B.D" etc. but not "A.BB", "B.A.B" etc. If
2237initialized with the empty string, all events are passed.
2238
2239
2240.. class:: Filter([name])
2241
2242 Returns an instance of the :class:`Filter` class. If *name* is specified, it
2243 names a logger which, together with its children, will have its events allowed
2244 through the filter. If no name is specified, allows every event.
2245
2246
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002247 .. method:: filter(record)
Georg Brandl8ec7f652007-08-15 14:28:01 +00002248
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002249 Is the specified record to be logged? Returns zero for no, nonzero for
2250 yes. If deemed appropriate, the record may be modified in-place by this
2251 method.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002252
2253
2254LogRecord Objects
2255-----------------
2256
2257:class:`LogRecord` instances are created every time something is logged. They
2258contain all the information pertinent to the event being logged. The main
2259information passed in is in msg and args, which are combined using msg % args to
2260create the message field of the record. The record also includes information
2261such as when the record was created, the source line where the logging call was
2262made, and any exception information to be logged.
2263
2264
2265.. class:: LogRecord(name, lvl, pathname, lineno, msg, args, exc_info [, func])
2266
2267 Returns an instance of :class:`LogRecord` initialized with interesting
2268 information. The *name* is the logger name; *lvl* is the numeric level;
2269 *pathname* is the absolute pathname of the source file in which the logging
2270 call was made; *lineno* is the line number in that file where the logging
2271 call is found; *msg* is the user-supplied message (a format string); *args*
2272 is the tuple which, together with *msg*, makes up the user message; and
2273 *exc_info* is the exception tuple obtained by calling :func:`sys.exc_info`
2274 (or :const:`None`, if no exception information is available). The *func* is
2275 the name of the function from which the logging call was made. If not
2276 specified, it defaults to ``None``.
2277
2278 .. versionchanged:: 2.5
2279 *func* was added.
2280
2281
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002282 .. method:: getMessage()
Georg Brandl8ec7f652007-08-15 14:28:01 +00002283
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002284 Returns the message for this :class:`LogRecord` instance after merging any
2285 user-supplied arguments with the message.
2286
Georg Brandl8ec7f652007-08-15 14:28:01 +00002287
Vinay Sajipc7403352008-01-18 15:54:14 +00002288LoggerAdapter Objects
2289---------------------
2290
2291.. versionadded:: 2.6
2292
2293:class:`LoggerAdapter` instances are used to conveniently pass contextual
Vinay Sajip733024a2008-01-21 17:39:22 +00002294information into logging calls. For a usage example , see the section on
2295`adding contextual information to your logging output`__.
2296
2297__ context-info_
Vinay Sajipc7403352008-01-18 15:54:14 +00002298
2299.. class:: LoggerAdapter(logger, extra)
2300
2301 Returns an instance of :class:`LoggerAdapter` initialized with an
2302 underlying :class:`Logger` instance and a dict-like object.
2303
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002304 .. method:: process(msg, kwargs)
Vinay Sajipc7403352008-01-18 15:54:14 +00002305
Benjamin Petersonc7b05922008-04-25 01:29:10 +00002306 Modifies the message and/or keyword arguments passed to a logging call in
2307 order to insert contextual information. This implementation takes the object
2308 passed as *extra* to the constructor and adds it to *kwargs* using key
2309 'extra'. The return value is a (*msg*, *kwargs*) tuple which has the
2310 (possibly modified) versions of the arguments passed in.
Vinay Sajipc7403352008-01-18 15:54:14 +00002311
2312In addition to the above, :class:`LoggerAdapter` supports all the logging
2313methods of :class:`Logger`, i.e. :meth:`debug`, :meth:`info`, :meth:`warning`,
2314:meth:`error`, :meth:`exception`, :meth:`critical` and :meth:`log`. These
2315methods have the same signatures as their counterparts in :class:`Logger`, so
2316you can use the two types of instances interchangeably.
2317
Georg Brandl8ec7f652007-08-15 14:28:01 +00002318
2319Thread Safety
2320-------------
2321
2322The logging module is intended to be thread-safe without any special work
2323needing to be done by its clients. It achieves this though using threading
2324locks; there is one lock to serialize access to the module's shared data, and
2325each handler also creates a lock to serialize access to its underlying I/O.
2326
2327
2328Configuration
2329-------------
2330
2331
2332.. _logging-config-api:
2333
2334Configuration functions
2335^^^^^^^^^^^^^^^^^^^^^^^
2336
Georg Brandl8ec7f652007-08-15 14:28:01 +00002337The following functions configure the logging module. They are located in the
2338:mod:`logging.config` module. Their use is optional --- you can configure the
2339logging module using these functions or by making calls to the main API (defined
2340in :mod:`logging` itself) and defining handlers which are declared either in
2341:mod:`logging` or :mod:`logging.handlers`.
2342
2343
2344.. function:: fileConfig(fname[, defaults])
2345
Vinay Sajip51104862009-01-02 18:53:04 +00002346 Reads the logging configuration from a :mod:`ConfigParser`\-format file named
2347 *fname*. This function can be called several times from an application,
2348 allowing an end user the ability to select from various pre-canned
2349 configurations (if the developer provides a mechanism to present the choices
2350 and load the chosen configuration). Defaults to be passed to the ConfigParser
2351 can be specified in the *defaults* argument.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002352
2353
2354.. function:: listen([port])
2355
2356 Starts up a socket server on the specified port, and listens for new
2357 configurations. If no port is specified, the module's default
2358 :const:`DEFAULT_LOGGING_CONFIG_PORT` is used. Logging configurations will be
2359 sent as a file suitable for processing by :func:`fileConfig`. Returns a
2360 :class:`Thread` instance on which you can call :meth:`start` to start the
2361 server, and which you can :meth:`join` when appropriate. To stop the server,
Georg Brandlc37f2882007-12-04 17:46:27 +00002362 call :func:`stopListening`.
2363
2364 To send a configuration to the socket, read in the configuration file and
2365 send it to the socket as a string of bytes preceded by a four-byte length
2366 string packed in binary using ``struct.pack('>L', n)``.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002367
2368
2369.. function:: stopListening()
2370
Georg Brandlc37f2882007-12-04 17:46:27 +00002371 Stops the listening server which was created with a call to :func:`listen`.
2372 This is typically called before calling :meth:`join` on the return value from
Georg Brandl8ec7f652007-08-15 14:28:01 +00002373 :func:`listen`.
2374
2375
2376.. _logging-config-fileformat:
2377
2378Configuration file format
2379^^^^^^^^^^^^^^^^^^^^^^^^^
2380
Georg Brandl392c6fc2008-05-25 07:25:25 +00002381The configuration file format understood by :func:`fileConfig` is based on
Vinay Sajip51104862009-01-02 18:53:04 +00002382:mod:`ConfigParser` functionality. The file must contain sections called
2383``[loggers]``, ``[handlers]`` and ``[formatters]`` which identify by name the
2384entities of each type which are defined in the file. For each such entity,
2385there is a separate section which identifies how that entity is configured.
2386Thus, for a logger named ``log01`` in the ``[loggers]`` section, the relevant
2387configuration details are held in a section ``[logger_log01]``. Similarly, a
2388handler called ``hand01`` in the ``[handlers]`` section will have its
2389configuration held in a section called ``[handler_hand01]``, while a formatter
2390called ``form01`` in the ``[formatters]`` section will have its configuration
2391specified in a section called ``[formatter_form01]``. The root logger
2392configuration must be specified in a section called ``[logger_root]``.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002393
2394Examples of these sections in the file are given below. ::
2395
2396 [loggers]
2397 keys=root,log02,log03,log04,log05,log06,log07
2398
2399 [handlers]
2400 keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09
2401
2402 [formatters]
2403 keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
2404
2405The root logger must specify a level and a list of handlers. An example of a
2406root logger section is given below. ::
2407
2408 [logger_root]
2409 level=NOTSET
2410 handlers=hand01
2411
2412The ``level`` entry can be one of ``DEBUG, INFO, WARNING, ERROR, CRITICAL`` or
2413``NOTSET``. For the root logger only, ``NOTSET`` means that all messages will be
2414logged. Level values are :func:`eval`\ uated in the context of the ``logging``
2415package's namespace.
2416
2417The ``handlers`` entry is a comma-separated list of handler names, which must
2418appear in the ``[handlers]`` section. These names must appear in the
2419``[handlers]`` section and have corresponding sections in the configuration
2420file.
2421
2422For loggers other than the root logger, some additional information is required.
2423This is illustrated by the following example. ::
2424
2425 [logger_parser]
2426 level=DEBUG
2427 handlers=hand01
2428 propagate=1
2429 qualname=compiler.parser
2430
2431The ``level`` and ``handlers`` entries are interpreted as for the root logger,
2432except that if a non-root logger's level is specified as ``NOTSET``, the system
2433consults loggers higher up the hierarchy to determine the effective level of the
2434logger. The ``propagate`` entry is set to 1 to indicate that messages must
2435propagate to handlers higher up the logger hierarchy from this logger, or 0 to
2436indicate that messages are **not** propagated to handlers up the hierarchy. The
2437``qualname`` entry is the hierarchical channel name of the logger, that is to
2438say the name used by the application to get the logger.
2439
2440Sections which specify handler configuration are exemplified by the following.
2441::
2442
2443 [handler_hand01]
2444 class=StreamHandler
2445 level=NOTSET
2446 formatter=form01
2447 args=(sys.stdout,)
2448
2449The ``class`` entry indicates the handler's class (as determined by :func:`eval`
2450in the ``logging`` package's namespace). The ``level`` is interpreted as for
2451loggers, and ``NOTSET`` is taken to mean "log everything".
2452
Vinay Sajip2a649f92008-07-18 09:00:35 +00002453.. versionchanged:: 2.6
2454 Added support for resolving the handler's class as a dotted module and class
2455 name.
2456
Georg Brandl8ec7f652007-08-15 14:28:01 +00002457The ``formatter`` entry indicates the key name of the formatter for this
2458handler. If blank, a default formatter (``logging._defaultFormatter``) is used.
2459If a name is specified, it must appear in the ``[formatters]`` section and have
2460a corresponding section in the configuration file.
2461
2462The ``args`` entry, when :func:`eval`\ uated in the context of the ``logging``
2463package's namespace, is the list of arguments to the constructor for the handler
2464class. Refer to the constructors for the relevant handlers, or to the examples
2465below, to see how typical entries are constructed. ::
2466
2467 [handler_hand02]
2468 class=FileHandler
2469 level=DEBUG
2470 formatter=form02
2471 args=('python.log', 'w')
2472
2473 [handler_hand03]
2474 class=handlers.SocketHandler
2475 level=INFO
2476 formatter=form03
2477 args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)
2478
2479 [handler_hand04]
2480 class=handlers.DatagramHandler
2481 level=WARN
2482 formatter=form04
2483 args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)
2484
2485 [handler_hand05]
2486 class=handlers.SysLogHandler
2487 level=ERROR
2488 formatter=form05
2489 args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)
2490
2491 [handler_hand06]
2492 class=handlers.NTEventLogHandler
2493 level=CRITICAL
2494 formatter=form06
2495 args=('Python Application', '', 'Application')
2496
2497 [handler_hand07]
2498 class=handlers.SMTPHandler
2499 level=WARN
2500 formatter=form07
2501 args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
2502
2503 [handler_hand08]
2504 class=handlers.MemoryHandler
2505 level=NOTSET
2506 formatter=form08
2507 target=
2508 args=(10, ERROR)
2509
2510 [handler_hand09]
2511 class=handlers.HTTPHandler
2512 level=NOTSET
2513 formatter=form09
2514 args=('localhost:9022', '/log', 'GET')
2515
2516Sections which specify formatter configuration are typified by the following. ::
2517
2518 [formatter_form01]
2519 format=F1 %(asctime)s %(levelname)s %(message)s
2520 datefmt=
2521 class=logging.Formatter
2522
2523The ``format`` entry is the overall format string, and the ``datefmt`` entry is
Georg Brandlb19be572007-12-29 10:57:00 +00002524the :func:`strftime`\ -compatible date/time format string. If empty, the
2525package substitutes ISO8601 format date/times, which is almost equivalent to
2526specifying the date format string ``"%Y-%m-%d %H:%M:%S"``. The ISO8601 format
2527also specifies milliseconds, which are appended to the result of using the above
2528format string, with a comma separator. An example time in ISO8601 format is
2529``2003-01-23 00:29:50,411``.
Georg Brandl8ec7f652007-08-15 14:28:01 +00002530
2531The ``class`` entry is optional. It indicates the name of the formatter's class
2532(as a dotted module and class name.) This option is useful for instantiating a
2533:class:`Formatter` subclass. Subclasses of :class:`Formatter` can present
2534exception tracebacks in an expanded or condensed format.
2535
Georg Brandlc37f2882007-12-04 17:46:27 +00002536
2537Configuration server example
2538^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2539
2540Here is an example of a module using the logging configuration server::
2541
2542 import logging
2543 import logging.config
2544 import time
2545 import os
2546
2547 # read initial config file
2548 logging.config.fileConfig("logging.conf")
2549
2550 # create and start listener on port 9999
2551 t = logging.config.listen(9999)
2552 t.start()
2553
2554 logger = logging.getLogger("simpleExample")
2555
2556 try:
2557 # loop through logging calls to see the difference
2558 # new configurations make, until Ctrl+C is pressed
2559 while True:
2560 logger.debug("debug message")
2561 logger.info("info message")
2562 logger.warn("warn message")
2563 logger.error("error message")
2564 logger.critical("critical message")
2565 time.sleep(5)
2566 except KeyboardInterrupt:
2567 # cleanup
2568 logging.config.stopListening()
2569 t.join()
2570
2571And here is a script that takes a filename and sends that file to the server,
2572properly preceded with the binary-encoded length, as the new logging
2573configuration::
2574
2575 #!/usr/bin/env python
2576 import socket, sys, struct
2577
2578 data_to_send = open(sys.argv[1], "r").read()
2579
2580 HOST = 'localhost'
2581 PORT = 9999
2582 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
2583 print "connecting..."
2584 s.connect((HOST, PORT))
2585 print "sending config..."
2586 s.send(struct.pack(">L", len(data_to_send)))
2587 s.send(data_to_send)
2588 s.close()
2589 print "complete"
2590
2591
2592More examples
2593-------------
2594
2595Multiple handlers and formatters
2596^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2597
2598Loggers are plain Python objects. The :func:`addHandler` method has no minimum
2599or maximum quota for the number of handlers you may add. Sometimes it will be
2600beneficial for an application to log all messages of all severities to a text
2601file while simultaneously logging errors or above to the console. To set this
2602up, simply configure the appropriate handlers. The logging calls in the
2603application code will remain unchanged. Here is a slight modification to the
2604previous simple module-based configuration example::
2605
2606 import logging
2607
2608 logger = logging.getLogger("simple_example")
2609 logger.setLevel(logging.DEBUG)
2610 # create file handler which logs even debug messages
2611 fh = logging.FileHandler("spam.log")
2612 fh.setLevel(logging.DEBUG)
2613 # create console handler with a higher log level
2614 ch = logging.StreamHandler()
2615 ch.setLevel(logging.ERROR)
2616 # create formatter and add it to the handlers
2617 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2618 ch.setFormatter(formatter)
2619 fh.setFormatter(formatter)
2620 # add the handlers to logger
2621 logger.addHandler(ch)
2622 logger.addHandler(fh)
2623
2624 # "application" code
2625 logger.debug("debug message")
2626 logger.info("info message")
2627 logger.warn("warn message")
2628 logger.error("error message")
2629 logger.critical("critical message")
2630
2631Notice that the "application" code does not care about multiple handlers. All
2632that changed was the addition and configuration of a new handler named *fh*.
2633
2634The ability to create new handlers with higher- or lower-severity filters can be
2635very helpful when writing and testing an application. Instead of using many
2636``print`` statements for debugging, use ``logger.debug``: Unlike the print
2637statements, which you will have to delete or comment out later, the logger.debug
2638statements can remain intact in the source code and remain dormant until you
2639need them again. At that time, the only change that needs to happen is to
2640modify the severity level of the logger and/or handler to debug.
2641
2642
2643Using logging in multiple modules
2644^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2645
2646It was mentioned above that multiple calls to
2647``logging.getLogger('someLogger')`` return a reference to the same logger
2648object. This is true not only within the same module, but also across modules
2649as long as it is in the same Python interpreter process. It is true for
2650references to the same object; additionally, application code can define and
2651configure a parent logger in one module and create (but not configure) a child
2652logger in a separate module, and all logger calls to the child will pass up to
2653the parent. Here is a main module::
2654
2655 import logging
2656 import auxiliary_module
2657
2658 # create logger with "spam_application"
2659 logger = logging.getLogger("spam_application")
2660 logger.setLevel(logging.DEBUG)
2661 # create file handler which logs even debug messages
2662 fh = logging.FileHandler("spam.log")
2663 fh.setLevel(logging.DEBUG)
2664 # create console handler with a higher log level
2665 ch = logging.StreamHandler()
2666 ch.setLevel(logging.ERROR)
2667 # create formatter and add it to the handlers
2668 formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
2669 fh.setFormatter(formatter)
2670 ch.setFormatter(formatter)
2671 # add the handlers to the logger
2672 logger.addHandler(fh)
2673 logger.addHandler(ch)
2674
2675 logger.info("creating an instance of auxiliary_module.Auxiliary")
2676 a = auxiliary_module.Auxiliary()
2677 logger.info("created an instance of auxiliary_module.Auxiliary")
2678 logger.info("calling auxiliary_module.Auxiliary.do_something")
2679 a.do_something()
2680 logger.info("finished auxiliary_module.Auxiliary.do_something")
2681 logger.info("calling auxiliary_module.some_function()")
2682 auxiliary_module.some_function()
2683 logger.info("done with auxiliary_module.some_function()")
2684
2685Here is the auxiliary module::
2686
2687 import logging
2688
2689 # create logger
2690 module_logger = logging.getLogger("spam_application.auxiliary")
2691
2692 class Auxiliary:
2693 def __init__(self):
2694 self.logger = logging.getLogger("spam_application.auxiliary.Auxiliary")
2695 self.logger.info("creating an instance of Auxiliary")
2696 def do_something(self):
2697 self.logger.info("doing something")
2698 a = 1 + 1
2699 self.logger.info("done doing something")
2700
2701 def some_function():
2702 module_logger.info("received a call to \"some_function\"")
2703
2704The output looks like this::
2705
Vinay Sajipe28fa292008-01-07 15:30:36 +00002706 2005-03-23 23:47:11,663 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002707 creating an instance of auxiliary_module.Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002708 2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002709 creating an instance of Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002710 2005-03-23 23:47:11,665 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002711 created an instance of auxiliary_module.Auxiliary
Vinay Sajipe28fa292008-01-07 15:30:36 +00002712 2005-03-23 23:47:11,668 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002713 calling auxiliary_module.Auxiliary.do_something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002714 2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002715 doing something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002716 2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002717 done doing something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002718 2005-03-23 23:47:11,670 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002719 finished auxiliary_module.Auxiliary.do_something
Vinay Sajipe28fa292008-01-07 15:30:36 +00002720 2005-03-23 23:47:11,671 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002721 calling auxiliary_module.some_function()
Vinay Sajipe28fa292008-01-07 15:30:36 +00002722 2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002723 received a call to "some_function"
Vinay Sajipe28fa292008-01-07 15:30:36 +00002724 2005-03-23 23:47:11,673 - spam_application - INFO -
Georg Brandlc37f2882007-12-04 17:46:27 +00002725 done with auxiliary_module.some_function()
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