Python3.0 Tutorial 简体中文版

:mod:`logging` --- Logging facility for Python ============================================== .. module:: logging :synopsis: Flexible error logging system for applications. .. moduleauthor:: Vinay Sajip <vinay_sajip@red-dove.com> .. sectionauthor:: Vinay Sajip <vinay_sajip@red-dove.com> .. index:: pair: Errors; logging This module defines functions and classes which implement a flexible error logging system for applications. Logging is performed by calling methods on instances of the :class:`Logger` class (hereafter called :dfn:`loggers`). Each instance has a name, and they are conceptually arranged in a namespace hierarchy using dots (periods) as separators. For example, a logger named "scan" is the parent of loggers "scan.text", "scan.html" and "scan.pdf". Logger names can be anything you want, and indicate the area of an application in which a logged message originates. Logged messages also have levels of importance associated with them. The default levels provided are :const:`DEBUG`, :const:`INFO`, :const:`WARNING`, :const:`ERROR` and :const:`CRITICAL`. As a convenience, you indicate the importance of a logged message by calling an appropriate method of :class:`Logger`. The methods are :meth:`debug`, :meth:`info`, :meth:`warning`, :meth:`error` and :meth:`critical`, which mirror the default levels. You are not constrained to use these levels: you can specify your own and use a more general :class:`Logger` method, :meth:`log`, which takes an explicit level argument. Logging tutorial ---------------- The key benefit of having the logging API provided by a standard library module is that all Python modules can participate in logging, so your application log can include messages from third-party modules. It is, of course, possible to log messages with different verbosity levels or to different destinations. Support for writing log messages to files, HTTP GET/POST locations, email via SMTP, generic sockets, or OS-specific logging mechanisms are all supported by the standard module. You can also create your own log destination class if you have special requirements not met by any of the built-in classes. Simple examples ^^^^^^^^^^^^^^^ .. sectionauthor:: Doug Hellmann .. (see <http://blog.doughellmann.com/2007/05/pymotw-logging.html>) Most applications are probably going to want to log to a file, so let's start with that case. Using the :func:`basicConfig` function, we can set up the default handler so that debug messages are written to a file:: import logging LOG_FILENAME = '/tmp/logging_example.out' logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG,) logging.debug('This message should go to the log file') And now if we open the file and look at what we have, we should find the log message:: DEBUG:root:This message should go to the log file If you run the script repeatedly, the additional log messages are appended to the file. To create a new file each time, you can pass a filemode argument to :func:`basicConfig` with a value of ``'w'``. Rather than managing the file size yourself, though, it is simpler to use a :class:`RotatingFileHandler`:: import glob import logging import logging.handlers LOG_FILENAME = '/tmp/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:: /tmp/logging_rotatingfile_example.out /tmp/logging_rotatingfile_example.out.1 /tmp/logging_rotatingfile_example.out.2 /tmp/logging_rotatingfile_example.out.3 /tmp/logging_rotatingfile_example.out.4 /tmp/logging_rotatingfile_example.out.5 The most current file is always :file:`/tmp/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 ``.5`` file is erased. Obviously this example sets the log length much much too small as an extreme example. You would want to set *maxBytes* to an appropriate value. Another useful feature of the logging API is the ability to produce different messages at different log levels. This allows you to instrument your code with debug messages, for example, but turning the log level down so that those debug messages are not written for your production system. The default levels are ``CRITICAL``, ``ERROR``, ``WARNING``, ``INFO``, ``DEBUG`` and ``UNSET``. The logger, handler, and log message call each specify a level. The log message is only emitted if the handler and logger are configured to emit messages of that level or lower. For example, if a message is ``CRITICAL``, and the logger is set to ``ERROR``, the message is emitted. If a message is a ``WARNING``, and the logger is set to produce only ``ERROR``\s, the message is not emitted:: import logging import sys LEVELS = {'debug': logging.DEBUG, 'info': logging.INFO, 'warning': logging.WARNING, 'error': logging.ERROR, 'critical': logging.CRITICAL} if len(sys.argv) > 1: level_name = sys.argv[1] level = LEVELS.get(level_name, logging.NOTSET) logging.basicConfig(level=level) logging.debug('This is a debug message') logging.info('This is an info message') logging.warning('This is a warning message') logging.error('This is an error message') logging.critical('This is a critical error message') Run the script with an argument like 'debug' or 'warning' to see which messages show up at different levels:: $ python logging_level_example.py debug DEBUG:root:This is a debug message INFO:root:This is an info message WARNING:root:This is a warning message ERROR:root:This is an error message CRITICAL:root:This is a critical error message $ python logging_level_example.py info INFO:root:This is an info message WARNING:root:This is a warning message ERROR:root:This is an error message CRITICAL:root:This is a critical error message You will notice that these log messages all have ``root`` embedded in them. The logging module supports a hierarchy of loggers with different names. An easy way to tell where a specific log message comes from is to use a separate logger object for each of your modules. Each new logger "inherits" the configuration of its parent, and log messages sent to a logger include the name of that logger. Optionally, each logger can be configured differently, so that messages from different modules are handled in different ways. Let's look at a simple example of how to log from different modules so it is easy to trace the source of the message:: import logging logging.basicConfig(level=logging.WARNING) logger1 = logging.getLogger('package1.module1') logger2 = logging.getLogger('package2.module2') logger1.warning('This message comes from one module') logger2.warning('And this message comes from another module') And the output:: $ python logging_modules_example.py WARNING:package1.module1:This message comes from one module WARNING:package2.module2:And this message comes from another module There are many more options for configuring logging, including different log message formatting options, having messages delivered to multiple destinations, and changing the configuration of a long-running application on the fly using a socket interface. All of these options are cov