793 lines
33 KiB
ReStructuredText
793 lines
33 KiB
ReStructuredText
.. _logging-cookbook:
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================
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Logging Cookbook
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================
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:Author: Vinay Sajip <vinay_sajip at red-dove dot com>
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This page contains a number of recipes related to logging, which have been found
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useful in the past.
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.. currentmodule:: logging
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Using logging in multiple modules
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---------------------------------
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Multiple calls to ``logging.getLogger('someLogger')`` return a reference to the
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same logger object. This is true not only within the same module, but also
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across modules as long as it is in the same Python interpreter process. It is
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true for references to the same object; additionally, application code can
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define and configure a parent logger in one module and create (but not
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configure) a child logger in a separate module, and all logger calls to the
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child will pass up to the parent. Here is a main module::
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import logging
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import auxiliary_module
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# create logger with 'spam_application'
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logger = logging.getLogger('spam_application')
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logger.setLevel(logging.DEBUG)
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# create file handler which logs even debug messages
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fh = logging.FileHandler('spam.log')
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fh.setLevel(logging.DEBUG)
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# create console handler with a higher log level
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ch = logging.StreamHandler()
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ch.setLevel(logging.ERROR)
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# create formatter and add it to the handlers
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formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
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fh.setFormatter(formatter)
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ch.setFormatter(formatter)
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# add the handlers to the logger
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logger.addHandler(fh)
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logger.addHandler(ch)
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logger.info('creating an instance of auxiliary_module.Auxiliary')
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a = auxiliary_module.Auxiliary()
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logger.info('created an instance of auxiliary_module.Auxiliary')
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logger.info('calling auxiliary_module.Auxiliary.do_something')
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a.do_something()
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logger.info('finished auxiliary_module.Auxiliary.do_something')
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logger.info('calling auxiliary_module.some_function()')
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auxiliary_module.some_function()
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logger.info('done with auxiliary_module.some_function()')
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Here is the auxiliary module::
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import logging
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# create logger
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module_logger = logging.getLogger('spam_application.auxiliary')
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class Auxiliary:
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def __init__(self):
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self.logger = logging.getLogger('spam_application.auxiliary.Auxiliary')
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self.logger.info('creating an instance of Auxiliary')
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def do_something(self):
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self.logger.info('doing something')
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a = 1 + 1
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self.logger.info('done doing something')
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def some_function():
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module_logger.info('received a call to "some_function"')
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The output looks like this::
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2005-03-23 23:47:11,663 - spam_application - INFO -
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creating an instance of auxiliary_module.Auxiliary
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2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
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creating an instance of Auxiliary
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2005-03-23 23:47:11,665 - spam_application - INFO -
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created an instance of auxiliary_module.Auxiliary
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2005-03-23 23:47:11,668 - spam_application - INFO -
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calling auxiliary_module.Auxiliary.do_something
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2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
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doing something
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2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
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done doing something
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2005-03-23 23:47:11,670 - spam_application - INFO -
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finished auxiliary_module.Auxiliary.do_something
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2005-03-23 23:47:11,671 - spam_application - INFO -
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calling auxiliary_module.some_function()
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2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
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received a call to 'some_function'
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2005-03-23 23:47:11,673 - spam_application - INFO -
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done with auxiliary_module.some_function()
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Multiple handlers and formatters
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--------------------------------
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Loggers are plain Python objects. The :func:`addHandler` method has no minimum
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or maximum quota for the number of handlers you may add. Sometimes it will be
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beneficial for an application to log all messages of all severities to a text
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file while simultaneously logging errors or above to the console. To set this
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up, simply configure the appropriate handlers. The logging calls in the
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application code will remain unchanged. Here is a slight modification to the
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previous simple module-based configuration example::
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import logging
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logger = logging.getLogger('simple_example')
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logger.setLevel(logging.DEBUG)
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# create file handler which logs even debug messages
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fh = logging.FileHandler('spam.log')
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fh.setLevel(logging.DEBUG)
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# create console handler with a higher log level
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ch = logging.StreamHandler()
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ch.setLevel(logging.ERROR)
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# create formatter and add it to the handlers
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formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
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ch.setFormatter(formatter)
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fh.setFormatter(formatter)
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# add the handlers to logger
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logger.addHandler(ch)
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logger.addHandler(fh)
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# 'application' code
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logger.debug('debug message')
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logger.info('info message')
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logger.warn('warn message')
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logger.error('error message')
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logger.critical('critical message')
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Notice that the 'application' code does not care about multiple handlers. All
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that changed was the addition and configuration of a new handler named *fh*.
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The ability to create new handlers with higher- or lower-severity filters can be
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very helpful when writing and testing an application. Instead of using many
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``print`` statements for debugging, use ``logger.debug``: Unlike the print
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statements, which you will have to delete or comment out later, the logger.debug
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statements can remain intact in the source code and remain dormant until you
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need them again. At that time, the only change that needs to happen is to
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modify the severity level of the logger and/or handler to debug.
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.. _multiple-destinations:
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Logging to multiple destinations
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--------------------------------
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Let's say you want to log to console and file with different message formats and
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in differing circumstances. Say you want to log messages with levels of DEBUG
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and higher to file, and those messages at level INFO and higher to the console.
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Let's also assume that the file should contain timestamps, but the console
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messages should not. Here's how you can achieve this::
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import logging
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# set up logging to file - see previous section for more details
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logging.basicConfig(level=logging.DEBUG,
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format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
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datefmt='%m-%d %H:%M',
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filename='/temp/myapp.log',
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filemode='w')
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# define a Handler which writes INFO messages or higher to the sys.stderr
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console = logging.StreamHandler()
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console.setLevel(logging.INFO)
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# set a format which is simpler for console use
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formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
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# tell the handler to use this format
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console.setFormatter(formatter)
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# add the handler to the root logger
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logging.getLogger('').addHandler(console)
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# Now, we can log to the root logger, or any other logger. First the root...
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logging.info('Jackdaws love my big sphinx of quartz.')
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# Now, define a couple of other loggers which might represent areas in your
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# application:
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logger1 = logging.getLogger('myapp.area1')
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logger2 = logging.getLogger('myapp.area2')
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logger1.debug('Quick zephyrs blow, vexing daft Jim.')
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logger1.info('How quickly daft jumping zebras vex.')
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logger2.warning('Jail zesty vixen who grabbed pay from quack.')
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logger2.error('The five boxing wizards jump quickly.')
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When you run this, on the console you will see ::
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root : INFO Jackdaws love my big sphinx of quartz.
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myapp.area1 : INFO How quickly daft jumping zebras vex.
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myapp.area2 : WARNING Jail zesty vixen who grabbed pay from quack.
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myapp.area2 : ERROR The five boxing wizards jump quickly.
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and in the file you will see something like ::
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10-22 22:19 root INFO Jackdaws love my big sphinx of quartz.
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10-22 22:19 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
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10-22 22:19 myapp.area1 INFO How quickly daft jumping zebras vex.
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10-22 22:19 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
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10-22 22:19 myapp.area2 ERROR The five boxing wizards jump quickly.
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As you can see, the DEBUG message only shows up in the file. The other messages
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are sent to both destinations.
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This example uses console and file handlers, but you can use any number and
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combination of handlers you choose.
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Configuration server example
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----------------------------
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Here is an example of a module using the logging configuration server::
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import logging
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import logging.config
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import time
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import os
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# read initial config file
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logging.config.fileConfig('logging.conf')
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# create and start listener on port 9999
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t = logging.config.listen(9999)
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t.start()
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logger = logging.getLogger('simpleExample')
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try:
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# loop through logging calls to see the difference
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# new configurations make, until Ctrl+C is pressed
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while True:
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logger.debug('debug message')
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logger.info('info message')
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logger.warn('warn message')
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logger.error('error message')
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logger.critical('critical message')
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time.sleep(5)
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except KeyboardInterrupt:
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# cleanup
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logging.config.stopListening()
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t.join()
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And here is a script that takes a filename and sends that file to the server,
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properly preceded with the binary-encoded length, as the new logging
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configuration::
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#!/usr/bin/env python
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import socket, sys, struct
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with open(sys.argv[1], 'rb') as f:
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data_to_send = f.read()
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HOST = 'localhost'
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PORT = 9999
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s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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print('connecting...')
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s.connect((HOST, PORT))
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print('sending config...')
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s.send(struct.pack('>L', len(data_to_send)))
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s.send(data_to_send)
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s.close()
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print('complete')
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.. _network-logging:
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Sending and receiving logging events across a network
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-----------------------------------------------------
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Let's say you want to send logging events across a network, and handle them at
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the receiving end. A simple way of doing this is attaching a
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:class:`SocketHandler` instance to the root logger at the sending end::
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import logging, logging.handlers
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rootLogger = logging.getLogger('')
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rootLogger.setLevel(logging.DEBUG)
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socketHandler = logging.handlers.SocketHandler('localhost',
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logging.handlers.DEFAULT_TCP_LOGGING_PORT)
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# don't bother with a formatter, since a socket handler sends the event as
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# an unformatted pickle
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rootLogger.addHandler(socketHandler)
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# Now, we can log to the root logger, or any other logger. First the root...
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logging.info('Jackdaws love my big sphinx of quartz.')
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# Now, define a couple of other loggers which might represent areas in your
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# application:
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logger1 = logging.getLogger('myapp.area1')
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logger2 = logging.getLogger('myapp.area2')
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logger1.debug('Quick zephyrs blow, vexing daft Jim.')
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logger1.info('How quickly daft jumping zebras vex.')
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logger2.warning('Jail zesty vixen who grabbed pay from quack.')
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logger2.error('The five boxing wizards jump quickly.')
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At the receiving end, you can set up a receiver using the :mod:`socketserver`
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module. Here is a basic working example::
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import pickle
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import logging
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import logging.handlers
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import socketserver
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import struct
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class LogRecordStreamHandler(socketserver.StreamRequestHandler):
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"""Handler for a streaming logging request.
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This basically logs the record using whatever logging policy is
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configured locally.
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"""
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def handle(self):
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"""
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Handle multiple requests - each expected to be a 4-byte length,
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followed by the LogRecord in pickle format. Logs the record
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according to whatever policy is configured locally.
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"""
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while True:
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chunk = self.connection.recv(4)
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if len(chunk) < 4:
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break
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slen = struct.unpack('>L', chunk)[0]
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chunk = self.connection.recv(slen)
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while len(chunk) < slen:
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chunk = chunk + self.connection.recv(slen - len(chunk))
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obj = self.unPickle(chunk)
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record = logging.makeLogRecord(obj)
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self.handleLogRecord(record)
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def unPickle(self, data):
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return pickle.loads(data)
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def handleLogRecord(self, record):
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# if a name is specified, we use the named logger rather than the one
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# implied by the record.
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if self.server.logname is not None:
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name = self.server.logname
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else:
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name = record.name
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logger = logging.getLogger(name)
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# N.B. EVERY record gets logged. This is because Logger.handle
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# is normally called AFTER logger-level filtering. If you want
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# to do filtering, do it at the client end to save wasting
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# cycles and network bandwidth!
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logger.handle(record)
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class LogRecordSocketReceiver(socketserver.ThreadingTCPServer):
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"""
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Simple TCP socket-based logging receiver suitable for testing.
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"""
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allow_reuse_address = 1
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def __init__(self, host='localhost',
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port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
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handler=LogRecordStreamHandler):
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socketserver.ThreadingTCPServer.__init__(self, (host, port), handler)
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self.abort = 0
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self.timeout = 1
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self.logname = None
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def serve_until_stopped(self):
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import select
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abort = 0
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while not abort:
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rd, wr, ex = select.select([self.socket.fileno()],
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[], [],
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self.timeout)
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if rd:
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self.handle_request()
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abort = self.abort
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def main():
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logging.basicConfig(
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format='%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s')
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tcpserver = LogRecordSocketReceiver()
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print('About to start TCP server...')
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tcpserver.serve_until_stopped()
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if __name__ == '__main__':
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main()
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First run the server, and then the client. On the client side, nothing is
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printed on the console; on the server side, you should see something like::
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About to start TCP server...
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59 root INFO Jackdaws love my big sphinx of quartz.
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59 myapp.area1 DEBUG Quick zephyrs blow, vexing daft Jim.
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69 myapp.area1 INFO How quickly daft jumping zebras vex.
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69 myapp.area2 WARNING Jail zesty vixen who grabbed pay from quack.
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69 myapp.area2 ERROR The five boxing wizards jump quickly.
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Note that there are some security issues with pickle in some scenarios. If
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these affect you, you can use an alternative serialization scheme by overriding
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the :meth:`makePickle` method and implementing your alternative there, as
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well as adapting the above script to use your alternative serialization.
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.. _context-info:
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Adding contextual information to your logging output
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----------------------------------------------------
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Sometimes you want logging output to contain contextual information in
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addition to the parameters passed to the logging call. For example, in a
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networked application, it may be desirable to log client-specific information
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in the log (e.g. remote client's username, or IP address). Although you could
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use the *extra* parameter to achieve this, it's not always convenient to pass
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the information in this way. While it might be tempting to create
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:class:`Logger` instances on a per-connection basis, this is not a good idea
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because these instances are not garbage collected. While this is not a problem
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in practice, when the number of :class:`Logger` instances is dependent on the
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level of granularity you want to use in logging an application, it could
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be hard to manage if the number of :class:`Logger` instances becomes
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effectively unbounded.
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Using LoggerAdapters to impart contextual information
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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An easy way in which you can pass contextual information to be output along
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with logging event information is to use the :class:`LoggerAdapter` class.
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This class is designed to look like a :class:`Logger`, so that you can call
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:meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error`,
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:meth:`exception`, :meth:`critical` and :meth:`log`. These methods have the
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same signatures as their counterparts in :class:`Logger`, so you can use the
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two types of instances interchangeably.
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When you create an instance of :class:`LoggerAdapter`, you pass it a
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:class:`Logger` instance and a dict-like object which contains your contextual
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information. When you call one of the logging methods on an instance of
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:class:`LoggerAdapter`, it delegates the call to the underlying instance of
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:class:`Logger` passed to its constructor, and arranges to pass the contextual
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information in the delegated call. Here's a snippet from the code of
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:class:`LoggerAdapter`::
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def debug(self, msg, *args, **kwargs):
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"""
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Delegate a debug call to the underlying logger, after adding
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contextual information from this adapter instance.
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"""
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msg, kwargs = self.process(msg, kwargs)
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self.logger.debug(msg, *args, **kwargs)
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The :meth:`process` method of :class:`LoggerAdapter` is where the contextual
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information is added to the logging output. It's passed the message and
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keyword arguments of the logging call, and it passes back (potentially)
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modified versions of these to use in the call to the underlying logger. The
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default implementation of this method leaves the message alone, but inserts
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an 'extra' key in the keyword argument whose value is the dict-like object
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passed to the constructor. Of course, if you had passed an 'extra' keyword
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argument in the call to the adapter, it will be silently overwritten.
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The advantage of using 'extra' is that the values in the dict-like object are
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merged into the :class:`LogRecord` instance's __dict__, allowing you to use
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customized strings with your :class:`Formatter` instances which know about
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the keys of the dict-like object. If you need a different method, e.g. if you
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want to prepend or append the contextual information to the message string,
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you just need to subclass :class:`LoggerAdapter` and override :meth:`process`
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to do what you need. Here's an example script which uses this class, which
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also illustrates what dict-like behaviour is needed from an arbitrary
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'dict-like' object for use in the constructor::
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import logging
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class ConnInfo:
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"""
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An example class which shows how an arbitrary class can be used as
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the 'extra' context information repository passed to a LoggerAdapter.
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"""
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def __getitem__(self, name):
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"""
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To allow this instance to look like a dict.
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"""
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from random import choice
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if name == 'ip':
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result = choice(['127.0.0.1', '192.168.0.1'])
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elif name == 'user':
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result = choice(['jim', 'fred', 'sheila'])
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else:
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result = self.__dict__.get(name, '?')
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return result
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def __iter__(self):
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"""
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To allow iteration over keys, which will be merged into
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the LogRecord dict before formatting and output.
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"""
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keys = ['ip', 'user']
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keys.extend(self.__dict__.keys())
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return keys.__iter__()
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if __name__ == '__main__':
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from random import choice
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levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
|
|
a1 = logging.LoggerAdapter(logging.getLogger('a.b.c'),
|
|
{ 'ip' : '123.231.231.123', 'user' : 'sheila' })
|
|
logging.basicConfig(level=logging.DEBUG,
|
|
format='%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s')
|
|
a1.debug('A debug message')
|
|
a1.info('An info message with %s', 'some parameters')
|
|
a2 = logging.LoggerAdapter(logging.getLogger('d.e.f'), ConnInfo())
|
|
for x in range(10):
|
|
lvl = choice(levels)
|
|
lvlname = logging.getLevelName(lvl)
|
|
a2.log(lvl, 'A message at %s level with %d %s', lvlname, 2, 'parameters')
|
|
|
|
When this script is run, the output should look something like this::
|
|
|
|
2008-01-18 14:49:54,023 a.b.c DEBUG IP: 123.231.231.123 User: sheila A debug message
|
|
2008-01-18 14:49:54,023 a.b.c INFO IP: 123.231.231.123 User: sheila An info message with some parameters
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
|
|
|
|
.. _filters-contextual:
|
|
|
|
Using Filters to impart contextual information
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
You can also add contextual information to log output using a user-defined
|
|
:class:`Filter`. ``Filter`` instances are allowed to modify the ``LogRecords``
|
|
passed to them, including adding additional attributes which can then be output
|
|
using a suitable format string, or if needed a custom :class:`Formatter`.
|
|
|
|
For example in a web application, the request being processed (or at least,
|
|
the interesting parts of it) can be stored in a threadlocal
|
|
(:class:`threading.local`) variable, and then accessed from a ``Filter`` to
|
|
add, say, information from the request - say, the remote IP address and remote
|
|
user's username - to the ``LogRecord``, using the attribute names 'ip' and
|
|
'user' as in the ``LoggerAdapter`` example above. In that case, the same format
|
|
string can be used to get similar output to that shown above. Here's an example
|
|
script::
|
|
|
|
import logging
|
|
from random import choice
|
|
|
|
class ContextFilter(logging.Filter):
|
|
"""
|
|
This is a filter which injects contextual information into the log.
|
|
|
|
Rather than use actual contextual information, we just use random
|
|
data in this demo.
|
|
"""
|
|
|
|
USERS = ['jim', 'fred', 'sheila']
|
|
IPS = ['123.231.231.123', '127.0.0.1', '192.168.0.1']
|
|
|
|
def filter(self, record):
|
|
|
|
record.ip = choice(ContextFilter.IPS)
|
|
record.user = choice(ContextFilter.USERS)
|
|
return True
|
|
|
|
if __name__ == '__main__':
|
|
levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
|
|
logging.basicConfig(level=logging.DEBUG,
|
|
format='%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s')
|
|
a1 = logging.getLogger('a.b.c')
|
|
a2 = logging.getLogger('d.e.f')
|
|
|
|
f = ContextFilter()
|
|
a1.addFilter(f)
|
|
a2.addFilter(f)
|
|
a1.debug('A debug message')
|
|
a1.info('An info message with %s', 'some parameters')
|
|
for x in range(10):
|
|
lvl = choice(levels)
|
|
lvlname = logging.getLevelName(lvl)
|
|
a2.log(lvl, 'A message at %s level with %d %s', lvlname, 2, 'parameters')
|
|
|
|
which, when run, produces something like::
|
|
|
|
2010-09-06 22:38:15,292 a.b.c DEBUG IP: 123.231.231.123 User: fred A debug message
|
|
2010-09-06 22:38:15,300 a.b.c INFO IP: 192.168.0.1 User: sheila An info message with some parameters
|
|
2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1 User: sheila A message at CRITICAL level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f ERROR IP: 127.0.0.1 User: jim A message at ERROR level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f DEBUG IP: 127.0.0.1 User: sheila A message at DEBUG level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f ERROR IP: 123.231.231.123 User: fred A message at ERROR level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 192.168.0.1 User: jim A message at CRITICAL level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1 User: sheila A message at CRITICAL level with 2 parameters
|
|
2010-09-06 22:38:15,300 d.e.f DEBUG IP: 192.168.0.1 User: jim A message at DEBUG level with 2 parameters
|
|
2010-09-06 22:38:15,301 d.e.f ERROR IP: 127.0.0.1 User: sheila A message at ERROR level with 2 parameters
|
|
2010-09-06 22:38:15,301 d.e.f DEBUG IP: 123.231.231.123 User: fred A message at DEBUG level with 2 parameters
|
|
2010-09-06 22:38:15,301 d.e.f INFO IP: 123.231.231.123 User: fred A message at INFO level with 2 parameters
|
|
|
|
|
|
.. _multiple-processes:
|
|
|
|
Logging to a single file from multiple processes
|
|
------------------------------------------------
|
|
|
|
Although logging is thread-safe, and logging to a single file from multiple
|
|
threads in a single process *is* supported, logging to a single file from
|
|
*multiple processes* is *not* supported, because there is no standard way to
|
|
serialize access to a single file across multiple processes in Python. If you
|
|
need to log to a single file from multiple processes, one way of doing this is
|
|
to have all the processes log to a :class:`SocketHandler`, and have a separate
|
|
process which implements a socket server which reads from the socket and logs
|
|
to file. (If you prefer, you can dedicate one thread in one of the existing
|
|
processes to perform this function.) :ref:`This section <network-logging>`
|
|
documents this approach in more detail and includes a working socket receiver
|
|
which can be used as a starting point for you to adapt in your own
|
|
applications.
|
|
|
|
If you are using a recent version of Python which includes the
|
|
:mod:`multiprocessing` module, you could write your own handler which uses the
|
|
:class:`Lock` class from this module to serialize access to the file from
|
|
your processes. The existing :class:`FileHandler` and subclasses do not make
|
|
use of :mod:`multiprocessing` at present, though they may do so in the future.
|
|
Note that at present, the :mod:`multiprocessing` module does not provide
|
|
working lock functionality on all platforms (see
|
|
http://bugs.python.org/issue3770).
|
|
|
|
.. currentmodule:: logging.handlers
|
|
|
|
|
|
Using file rotation
|
|
-------------------
|
|
|
|
.. sectionauthor:: Doug Hellmann, Vinay Sajip (changes)
|
|
.. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>)
|
|
|
|
Sometimes you want to let a log file grow to a certain size, then open a new
|
|
file and log to that. You may want to keep a certain number of these files, and
|
|
when that many files have been created, rotate the files so that the number of
|
|
files and the size of the files both remain bounded. For this usage pattern, the
|
|
logging package provides a :class:`RotatingFileHandler`::
|
|
|
|
import glob
|
|
import logging
|
|
import logging.handlers
|
|
|
|
LOG_FILENAME = 'logging_rotatingfile_example.out'
|
|
|
|
# Set up a specific logger with our desired output level
|
|
my_logger = logging.getLogger('MyLogger')
|
|
my_logger.setLevel(logging.DEBUG)
|
|
|
|
# Add the log message handler to the logger
|
|
handler = logging.handlers.RotatingFileHandler(
|
|
LOG_FILENAME, maxBytes=20, backupCount=5)
|
|
|
|
my_logger.addHandler(handler)
|
|
|
|
# Log some messages
|
|
for i in range(20):
|
|
my_logger.debug('i = %d' % i)
|
|
|
|
# See what files are created
|
|
logfiles = glob.glob('%s*' % LOG_FILENAME)
|
|
|
|
for filename in logfiles:
|
|
print(filename)
|
|
|
|
The result should be 6 separate files, each with part of the log history for the
|
|
application::
|
|
|
|
logging_rotatingfile_example.out
|
|
logging_rotatingfile_example.out.1
|
|
logging_rotatingfile_example.out.2
|
|
logging_rotatingfile_example.out.3
|
|
logging_rotatingfile_example.out.4
|
|
logging_rotatingfile_example.out.5
|
|
|
|
The most current file is always :file:`logging_rotatingfile_example.out`,
|
|
and each time it reaches the size limit it is renamed with the suffix
|
|
``.1``. Each of the existing backup files is renamed to increment the suffix
|
|
(``.1`` becomes ``.2``, etc.) and the ``.6`` file is erased.
|
|
|
|
Obviously this example sets the log length much too small as an extreme
|
|
example. You would want to set *maxBytes* to an appropriate value.
|
|
|
|
An example dictionary-based configuration
|
|
-----------------------------------------
|
|
|
|
Below is an example of a logging configuration dictionary - it's taken from
|
|
the `documentation on the Django project <https://docs.djangoproject.com/en/1.3/topics/logging/#configuring-logging>`_.
|
|
This dictionary is passed to :func:`~logging.config.dictConfig` to put the configuration into effect::
|
|
|
|
LOGGING = {
|
|
'version': 1,
|
|
'disable_existing_loggers': True,
|
|
'formatters': {
|
|
'verbose': {
|
|
'format': '%(levelname)s %(asctime)s %(module)s %(process)d %(thread)d %(message)s'
|
|
},
|
|
'simple': {
|
|
'format': '%(levelname)s %(message)s'
|
|
},
|
|
},
|
|
'filters': {
|
|
'special': {
|
|
'()': 'project.logging.SpecialFilter',
|
|
'foo': 'bar',
|
|
}
|
|
},
|
|
'handlers': {
|
|
'null': {
|
|
'level':'DEBUG',
|
|
'class':'django.utils.log.NullHandler',
|
|
},
|
|
'console':{
|
|
'level':'DEBUG',
|
|
'class':'logging.StreamHandler',
|
|
'formatter': 'simple'
|
|
},
|
|
'mail_admins': {
|
|
'level': 'ERROR',
|
|
'class': 'django.utils.log.AdminEmailHandler',
|
|
'filters': ['special']
|
|
}
|
|
},
|
|
'loggers': {
|
|
'django': {
|
|
'handlers':['null'],
|
|
'propagate': True,
|
|
'level':'INFO',
|
|
},
|
|
'django.request': {
|
|
'handlers': ['mail_admins'],
|
|
'level': 'ERROR',
|
|
'propagate': False,
|
|
},
|
|
'myproject.custom': {
|
|
'handlers': ['console', 'mail_admins'],
|
|
'level': 'INFO',
|
|
'filters': ['special']
|
|
}
|
|
}
|
|
}
|
|
|
|
For more information about this configuration, you can see the `relevant
|
|
section <https://docs.djangoproject.com/en/1.3/topics/logging/#configuring-logging>`_
|
|
of the Django documentation.
|
|
|
|
Inserting a BOM into messages sent to a SysLogHandler
|
|
-----------------------------------------------------
|
|
|
|
`RFC 5424 <http://tools.ietf.org/html/rfc5424>`_ requires that a
|
|
Unicode message be sent to a syslog daemon as a set of bytes which have the
|
|
following structure: an optional pure-ASCII component, followed by a UTF-8 Byte
|
|
Order Mark (BOM), followed by Unicode encoded using UTF-8. (See the `relevant
|
|
section of the specification <http://tools.ietf.org/html/rfc5424#section-6>`_.)
|
|
|
|
In Python 2.6 and 2.7, code was added to
|
|
:class:`~logging.handlers.SysLogHandler` to insert a BOM into the message, but
|
|
unfortunately, it was implemented incorrectly, with the BOM appearing at the
|
|
beginning of the message and hence not allowing any pure-ASCII component to
|
|
appear before it.
|
|
|
|
As this behaviour is broken, the incorrect BOM insertion code is being removed
|
|
from Python 2.7.4 and later. However, it is not being replaced, and if you
|
|
want to produce RFC 5424-compliant messages which includes a BOM, an optional
|
|
pure-ASCII sequence before it and arbitrary Unicode after it, encoded using
|
|
UTF-8, then you need to do the following:
|
|
|
|
#. Attach a :class:`~logging.Formatter` instance to your
|
|
:class:`~logging.handlers.SysLogHandler` instance, with a format string
|
|
such as::
|
|
|
|
u'ASCII section\ufeffUnicode section'
|
|
|
|
The Unicode code point ``u'\feff```, when encoded using UTF-8, will be
|
|
encoded as a UTF-8 BOM -- the byte-string ``'\xef\xbb\xbf'``.
|
|
|
|
#. Replace the ASCII section with whatever placeholders you like, but make sure
|
|
that the data that appears in there after substitution is always ASCII (that
|
|
way, it will remain unchanged after UTF-8 encoding).
|
|
|
|
#. Replace the Unicode section with whatever placeholders you like; if the data
|
|
which appears there after substitution is Unicode, that's fine -- it will be
|
|
encoded using UTF-8.
|
|
|
|
If the formatted message is Unicode, it *will* be encoded using UTF-8 encoding
|
|
by ``SysLogHandler``. If you follow the above rules, you should be able to
|
|
produce RFC 5424-compliant messages. If you don't, logging may not complain,
|
|
but your messages will not be RFC 5424-compliant, and your syslog daemon may
|
|
complain.
|
|
|