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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="color-scheme" content="light dark"> <title>PEP 337 – Logging Usage in the Standard Library | peps.python.org</title> <link rel="shortcut icon" href="../_static/py.png"> <link rel="canonical" href="https://peps.python.org/pep-0337/"> <link rel="stylesheet" href="../_static/style.css" type="text/css"> <link rel="stylesheet" href="../_static/mq.css" type="text/css"> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" media="(prefers-color-scheme: light)" id="pyg-light"> <link rel="stylesheet" href="../_static/pygments_dark.css" type="text/css" media="(prefers-color-scheme: dark)" id="pyg-dark"> <link rel="alternate" type="application/rss+xml" title="Latest PEPs" href="https://peps.python.org/peps.rss"> <meta property="og:title" content='PEP 337 – Logging Usage in the Standard Library | peps.python.org'> <meta property="og:description" content="This PEP defines a standard for using the logging system (PEP 282) in the standard library."> <meta property="og:type" content="website"> <meta property="og:url" content="https://peps.python.org/pep-0337/"> <meta property="og:site_name" content="Python Enhancement Proposals (PEPs)"> <meta property="og:image" content="https://peps.python.org/_static/og-image.png"> <meta property="og:image:alt" content="Python PEPs"> <meta property="og:image:width" content="200"> <meta property="og:image:height" content="200"> <meta name="description" content="This PEP defines a standard for using the logging system (PEP 282) in the standard library."> <meta name="theme-color" content="#3776ab"> </head> <body> <svg xmlns="http://www.w3.org/2000/svg" style="display: none;"> <symbol id="svg-sun-half" viewBox="0 0 24 24" pointer-events="all"> <title>Following system colour scheme</title> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"> <circle cx="12" cy="12" r="9"></circle> <path d="M12 3v18m0-12l4.65-4.65M12 14.3l7.37-7.37M12 19.6l8.85-8.85"></path> </svg> </symbol> <symbol id="svg-moon" viewBox="0 0 24 24" pointer-events="all"> <title>Selected dark colour scheme</title> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"> <path stroke="none" d="M0 0h24v24H0z" fill="none"></path> <path d="M12 3c.132 0 .263 0 .393 0a7.5 7.5 0 0 0 7.92 12.446a9 9 0 1 1 -8.313 -12.454z"></path> </svg> </symbol> <symbol id="svg-sun" viewBox="0 0 24 24" pointer-events="all"> <title>Selected light colour scheme</title> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"> <circle cx="12" cy="12" r="5"></circle> <line x1="12" y1="1" x2="12" y2="3"></line> <line x1="12" y1="21" x2="12" y2="23"></line> <line x1="4.22" y1="4.22" x2="5.64" y2="5.64"></line> <line x1="18.36" y1="18.36" x2="19.78" y2="19.78"></line> <line x1="1" y1="12" x2="3" y2="12"></line> <line x1="21" y1="12" x2="23" y2="12"></line> <line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line> <line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line> </svg> </symbol> </svg> <script> document.documentElement.dataset.colour_scheme = localStorage.getItem("colour_scheme") || "auto" </script> <section id="pep-page-section"> <header> <h1>Python Enhancement Proposals</h1> <ul class="breadcrumbs"> <li><a href="https://www.python.org/" title="The Python Programming Language">Python</a> » </li> <li><a href="../pep-0000/">PEP Index</a> » </li> <li>PEP 337</li> </ul> <button id="colour-scheme-cycler" onClick="setColourScheme(nextColourScheme())"> <svg aria-hidden="true" class="colour-scheme-icon-when-auto"><use href="#svg-sun-half"></use></svg> <svg aria-hidden="true" class="colour-scheme-icon-when-dark"><use href="#svg-moon"></use></svg> <svg aria-hidden="true" class="colour-scheme-icon-when-light"><use href="#svg-sun"></use></svg> <span class="visually-hidden">Toggle light / dark / auto colour theme</span> </button> </header> <article> <section id="pep-content"> <h1 class="page-title">PEP 337 – Logging Usage in the Standard Library</h1> <dl class="rfc2822 field-list simple"> <dt class="field-odd">Author<span class="colon">:</span></dt> <dd class="field-odd">Michael P. Dubner <dubnerm at mindless.com></dd> <dt class="field-even">Status<span class="colon">:</span></dt> <dd class="field-even"><abbr title="Inactive draft that may be taken up again at a later time">Deferred</abbr></dd> <dt class="field-odd">Type<span class="colon">:</span></dt> <dd class="field-odd"><abbr title="Normative PEP with a new feature for Python, implementation change for CPython or interoperability standard for the ecosystem">Standards Track</abbr></dd> <dt class="field-even">Created<span class="colon">:</span></dt> <dd class="field-even">02-Oct-2004</dd> <dt class="field-odd">Python-Version<span class="colon">:</span></dt> <dd class="field-odd">2.5</dd> <dt class="field-even">Post-History<span class="colon">:</span></dt> <dd class="field-even">10-Nov-2004</dd> </dl> <hr class="docutils" /> <section id="contents"> <details><summary>Table of Contents</summary><ul class="simple"> <li><a class="reference internal" href="#abstract">Abstract</a></li> <li><a class="reference internal" href="#pep-deferral">PEP Deferral</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#proposal">Proposal</a></li> <li><a class="reference internal" href="#module-list">Module List</a></li> <li><a class="reference internal" href="#doubtful-modules">Doubtful Modules</a></li> <li><a class="reference internal" href="#guidelines-for-logging-usage">Guidelines for Logging Usage</a></li> <li><a class="reference internal" href="#references">References</a></li> <li><a class="reference internal" href="#copyright">Copyright</a></li> </ul> </details></section> <section id="abstract"> <h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2> <p>This PEP defines a standard for using the logging system (<a class="pep reference internal" href="../pep-0282/" title="PEP 282 – A Logging System">PEP 282</a>) in the standard library.</p> <p>Implementing this PEP will simplify development of daemon applications. As a downside this PEP requires slight modifications (however in a back-portable way) to a large number of standard modules.</p> <p>After implementing this PEP one can use following filtering scheme:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s1">'py.BaseHTTPServer'</span><span class="p">)</span><span class="o">.</span><span class="n">setLevel</span><span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">FATAL</span><span class="p">)</span> </pre></div> </div> </section> <section id="pep-deferral"> <h2><a class="toc-backref" href="#pep-deferral" role="doc-backlink">PEP Deferral</a></h2> <p>Further exploration of the concepts covered in this PEP has been deferred for lack of a current champion interested in promoting the goals of the PEP and collecting and incorporating feedback, and with sufficient available time to do so effectively.</p> </section> <section id="rationale"> <h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2> <p>There are a couple of situations when output to stdout or stderr is impractical:</p> <ul class="simple"> <li>Daemon applications where the framework doesn’t allow the redirection of standard output to some file, but assumes use of some other form of logging. Examples are syslog under *nix’es and EventLog under WinNT+.</li> <li>GUI applications which want to output every new log entry in separate pop-up window (i.e. fading OSD).</li> </ul> <p>Also sometimes applications want to filter output entries based on their source or severity. This requirement can’t be implemented using simple redirection.</p> <p>Finally sometimes output needs to be marked with event timestamps, which can be accomplished with ease using the logging system.</p> </section> <section id="proposal"> <h2><a class="toc-backref" href="#proposal" role="doc-backlink">Proposal</a></h2> <p>Every module usable for daemon and GUI applications should be rewritten to use the logging system instead of <code class="docutils literal notranslate"><span class="pre">print</span></code> or <code class="docutils literal notranslate"><span class="pre">sys.stdout.write</span></code>.</p> <p>There should be code like this included in the beginning of every modified module:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">logging</span> <span class="n">_log</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s1">'py.<module-name>'</span><span class="p">)</span> </pre></div> </div> <p>A prefix of <code class="docutils literal notranslate"><span class="pre">py.</span></code> <a class="footnote-reference brackets" href="#id2" id="id1">[2]</a> must be used by all modules included in the standard library distributed along with Python, and only by such modules (unverifiable). The use of <code class="docutils literal notranslate"><span class="pre">_log</span></code> is intentional as we don’t want to auto-export it. For modules that use log only in one class a logger can be created inside the class definition as follows:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">XXX</span><span class="p">:</span> <span class="n">__log</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s1">'py.<module-name>'</span><span class="p">)</span> </pre></div> </div> <p>Then this class can create access methods to log to this private logger.</p> <p>So <code class="docutils literal notranslate"><span class="pre">print</span></code> and <code class="docutils literal notranslate"><span class="pre">sys.std{out|err}.write</span></code> statements should be replaced with <code class="docutils literal notranslate"><span class="pre">_log.{debug|info}</span></code>, and <code class="docutils literal notranslate"><span class="pre">traceback.print_exception</span></code> with <code class="docutils literal notranslate"><span class="pre">_log.exception</span></code> or sometimes <code class="docutils literal notranslate"><span class="pre">_log.debug('...',</span> <span class="pre">exc_info=1)</span></code>.</p> </section> <section id="module-list"> <h2><a class="toc-backref" href="#module-list" role="doc-backlink">Module List</a></h2> <p>Here is a (possibly incomplete) list of modules to be reworked:</p> <ul class="simple"> <li>asyncore (dispatcher.log, dispatcher.log_info)</li> <li>BaseHTTPServer (BaseHTTPRequestHandler.log_request, BaseHTTPRequestHandler.log_error, BaseHTTPRequestHandler.log_message)</li> <li>cgi (possibly - is cgi.log used by somebody?)</li> <li>ftplib (if FTP.debugging)</li> <li>gopherlib (get_directory)</li> <li>httplib (HTTPResponse, HTTPConnection)</li> <li>ihooks (_Verbose)</li> <li>imaplib (IMAP4._mesg)</li> <li>mhlib (MH.error)</li> <li>nntplib (NNTP)</li> <li>pipes (Template.makepipeline)</li> <li>pkgutil (extend_path)</li> <li>platform (_syscmd_ver)</li> <li>poplib (if POP3._debugging)</li> <li>profile (if Profile.verbose)</li> <li>robotparser (_debug)</li> <li>smtplib (if SGMLParser.verbose)</li> <li>shlex (if shlex.debug)</li> <li>smtpd (SMTPChannel/PureProxy where print >> DEBUGSTREAM)</li> <li>smtplib (if SMTP.debuglevel)</li> <li>SocketServer (BaseServer.handle_error)</li> <li>telnetlib (if Telnet.debuglevel)</li> <li>threading? (_Verbose._note, Thread.__bootstrap)</li> <li>timeit (Timer.print_exc)</li> <li>trace</li> <li>uu (decode)</li> </ul> <p>Additionally there are a couple of modules with commented debug output or modules where debug output should be added. For example:</p> <ul class="simple"> <li>urllib</li> </ul> <p>Finally possibly some modules should be extended to provide more debug information.</p> </section> <section id="doubtful-modules"> <h2><a class="toc-backref" href="#doubtful-modules" role="doc-backlink">Doubtful Modules</a></h2> <p>Listed here are modules that the community will propose for addition to the module list and modules that the community say should be removed from the module list.</p> <ul class="simple"> <li>tabnanny (check)</li> </ul> </section> <section id="guidelines-for-logging-usage"> <h2><a class="toc-backref" href="#guidelines-for-logging-usage" role="doc-backlink">Guidelines for Logging Usage</a></h2> <p>Also we can provide some recommendation to authors of library modules so they all follow the same format of naming loggers. I propose that non-standard library modules should use loggers named after their full names, so a module “spam” in sub-package “junk” of package “dummy” will be named “dummy.junk.spam” and, of course, the <code class="docutils literal notranslate"><span class="pre">__init__</span></code> module of the same sub-package will have the logger name “dummy.junk”.</p> </section> <section id="references"> <h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2> <aside class="footnote-list brackets"> <aside class="footnote brackets" id="id2" role="doc-footnote"> <dt class="label" id="id2">[<a href="#id1">2</a>]</dt> <dd><a class="reference external" href="https://mail.python.org/pipermail/python-dev/2004-October/049282.html">https://mail.python.org/pipermail/python-dev/2004-October/049282.html</a></aside> </aside> </section> <section id="copyright"> <h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2> <p>This document has been placed in the public domain.</p> </section> </section> <hr class="docutils" /> <p>Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0337.rst">https://github.com/python/peps/blob/main/peps/pep-0337.rst</a></p> <p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0337.rst">2025-02-01 08:59:27 GMT</a></p> </article> <nav id="pep-sidebar"> <h2>Contents</h2> <ul> <li><a class="reference internal" href="#abstract">Abstract</a></li> <li><a class="reference internal" href="#pep-deferral">PEP Deferral</a></li> <li><a class="reference internal" href="#rationale">Rationale</a></li> <li><a class="reference internal" href="#proposal">Proposal</a></li> <li><a class="reference internal" href="#module-list">Module List</a></li> <li><a class="reference internal" href="#doubtful-modules">Doubtful Modules</a></li> <li><a class="reference internal" href="#guidelines-for-logging-usage">Guidelines for Logging Usage</a></li> <li><a class="reference internal" href="#references">References</a></li> <li><a class="reference internal" href="#copyright">Copyright</a></li> </ul> <br> <a id="source" href="https://github.com/python/peps/blob/main/peps/pep-0337.rst">Page Source (GitHub)</a> </nav> </section> <script src="../_static/colour_scheme.js"></script> <script src="../_static/wrap_tables.js"></script> <script src="../_static/sticky_banner.js"></script> </body> </html>