209 lines
5.0 KiB
Plaintext
209 lines
5.0 KiB
Plaintext
PEP: 337
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Title: Logging Usage in the Standard Library
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Version: $Revision$
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Last-Modified: $Date$
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Author: Michael P. Dubner <dubnerm@mindless.com>
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Status: Deferred
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 02-Oct-2004
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Python-Version: 2.5
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Post-History: 10-Nov-2004
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Abstract
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========
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This PEP defines a standard for using the logging system (PEP 282 [1]_) in the
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standard library.
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Implementing this PEP will simplify development of daemon
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applications. As a downside this PEP requires slight
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modifications (however in a back-portable way) to a large number
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of standard modules.
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After implementing this PEP one can use following filtering
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scheme::
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logging.getLogger('py.BaseHTTPServer').setLevel(logging.FATAL)
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PEP Deferral
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============
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Further exploration of the concepts covered in this PEP has been deferred
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for lack of a current champion interested in promoting the goals of the
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PEP and collecting and incorporating feedback, and with sufficient
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available time to do so effectively.
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Rationale
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=========
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There are a couple of situations when output to stdout or stderr
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is impractical:
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- Daemon applications where the framework doesn't allow the
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redirection of standard output to some file, but assumes use of
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some other form of logging. Examples are syslog under \*nix'es
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and EventLog under WinNT+.
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- GUI applications which want to output every new log entry in
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separate pop-up window (i.e. fading OSD).
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Also sometimes applications want to filter output entries based on
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their source or severity. This requirement can't be implemented
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using simple redirection.
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Finally sometimes output needs to be marked with event timestamps,
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which can be accomplished with ease using the logging system.
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Proposal
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========
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Every module usable for daemon and GUI applications should be
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rewritten to use the logging system instead of ``print`` or
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``sys.stdout.write``.
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There should be code like this included in the beginning of every
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modified module::
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import logging
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_log = logging.getLogger('py.<module-name>')
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A prefix of ``py.`` [2]_ must be used by all modules included in the
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standard library distributed along with Python, and only by such
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modules (unverifiable). The use of ``_log`` is intentional as we
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don't want to auto-export it. For modules that use log only in
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one class a logger can be created inside the class definition as
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follows::
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class XXX:
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__log = logging.getLogger('py.<module-name>')
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Then this class can create access methods to log to this private
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logger.
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So ``print`` and ``sys.std{out|err}.write`` statements should be
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replaced with ``_log.{debug|info}``, and ``traceback.print_exception``
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with ``_log.exception`` or sometimes ``_log.debug('...', exc_info=1)``.
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Module List
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===========
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Here is a (possibly incomplete) list of modules to be reworked:
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- asyncore (dispatcher.log, dispatcher.log_info)
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- BaseHTTPServer (BaseHTTPRequestHandler.log_request,
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BaseHTTPRequestHandler.log_error,
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BaseHTTPRequestHandler.log_message)
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- cgi (possibly - is cgi.log used by somebody?)
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- ftplib (if FTP.debugging)
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- gopherlib (get_directory)
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- httplib (HTTPResponse, HTTPConnection)
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- ihooks (_Verbose)
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- imaplib (IMAP4._mesg)
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- mhlib (MH.error)
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- nntplib (NNTP)
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- pipes (Template.makepipeline)
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- pkgutil (extend_path)
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- platform (_syscmd_ver)
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- poplib (if POP3._debugging)
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- profile (if Profile.verbose)
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- robotparser (_debug)
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- smtplib (if SGMLParser.verbose)
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- shlex (if shlex.debug)
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- smtpd (SMTPChannel/PureProxy where print >> DEBUGSTREAM)
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- smtplib (if SMTP.debuglevel)
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- SocketServer (BaseServer.handle_error)
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- telnetlib (if Telnet.debuglevel)
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- threading? (_Verbose._note, Thread.__bootstrap)
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- timeit (Timer.print_exc)
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- trace
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- uu (decode)
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Additionally there are a couple of modules with commented debug
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output or modules where debug output should be added. For
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example:
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- urllib
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Finally possibly some modules should be extended to provide more
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debug information.
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Doubtful Modules
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================
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Listed here are modules that the community will propose for
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addition to the module list and modules that the community say
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should be removed from the module list.
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- tabnanny (check)
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Guidelines for Logging Usage
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============================
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Also we can provide some recommendation to authors of library
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modules so they all follow the same format of naming loggers. I
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propose that non-standard library modules should use loggers named
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after their full names, so a module "spam" in sub-package "junk"
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of package "dummy" will be named "dummy.junk.spam" and, of course,
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the ``__init__`` module of the same sub-package will have the logger
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name "dummy.junk".
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References
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==========
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.. [1] PEP 282, A Logging System, Vinay Sajip, Trent Mick
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http://www.python.org/dev/peps/pep-0282/
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.. [2] https://mail.python.org/pipermail/python-dev/2004-October/049282.html
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Copyright
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=========
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This document has been placed in the public domain.
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..
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Local Variables:
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End:
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