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<h1>Python Enhancement Proposals</h1>
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<h1 class="page-title">PEP 337 – Logging Usage in the Standard Library</h1>
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<dl class="rfc2822 field-list simple">
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<dt class="field-odd">Author<span class="colon">:</span></dt>
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<dd class="field-odd">Michael P. Dubner <dubnerm at mindless.com></dd>
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<dt class="field-even">Status<span class="colon">:</span></dt>
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<dd class="field-even"><abbr title="Inactive draft that may be taken up again at a later time">Deferred</abbr></dd>
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<dt class="field-odd">Type<span class="colon">:</span></dt>
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<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>
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<dt class="field-even">Created<span class="colon">:</span></dt>
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<dd class="field-even">02-Oct-2004</dd>
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<dt class="field-odd">Python-Version<span class="colon">:</span></dt>
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<dd class="field-odd">2.5</dd>
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<dt class="field-even">Post-History<span class="colon">:</span></dt>
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<dd class="field-even">10-Nov-2004</dd>
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<details><summary>Table of Contents</summary><ul class="simple">
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<li><a class="reference internal" href="#abstract">Abstract</a></li>
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<li><a class="reference internal" href="#pep-deferral">PEP Deferral</a></li>
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<li><a class="reference internal" href="#rationale">Rationale</a></li>
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<li><a class="reference internal" href="#proposal">Proposal</a></li>
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<li><a class="reference internal" href="#module-list">Module List</a></li>
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<li><a class="reference internal" href="#doubtful-modules">Doubtful Modules</a></li>
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<li><a class="reference internal" href="#guidelines-for-logging-usage">Guidelines for Logging Usage</a></li>
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<li><a class="reference internal" href="#references">References</a></li>
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<li><a class="reference internal" href="#copyright">Copyright</a></li>
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</details></section>
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<section id="abstract">
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<h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2>
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<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
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standard library.</p>
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<p>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.</p>
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<p>After implementing this PEP one can use following filtering
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scheme:</p>
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<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>
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</pre></div>
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</div>
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</section>
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<section id="pep-deferral">
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<h2><a class="toc-backref" href="#pep-deferral" role="doc-backlink">PEP Deferral</a></h2>
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<p>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.</p>
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</section>
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<section id="rationale">
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<h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2>
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<p>There are a couple of situations when output to stdout or stderr
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is impractical:</p>
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<ul class="simple">
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<li>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+.</li>
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<li>GUI applications which want to output every new log entry in
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separate pop-up window (i.e. fading OSD).</li>
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</ul>
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<p>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.</p>
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<p>Finally sometimes output needs to be marked with event timestamps,
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which can be accomplished with ease using the logging system.</p>
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</section>
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<section id="proposal">
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<h2><a class="toc-backref" href="#proposal" role="doc-backlink">Proposal</a></h2>
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<p>Every module usable for daemon and GUI applications should be
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rewritten to use the logging system instead of <code class="docutils literal notranslate"><span class="pre">print</span></code> or
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<code class="docutils literal notranslate"><span class="pre">sys.stdout.write</span></code>.</p>
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<p>There should be code like this included in the beginning of every
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modified module:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">logging</span>
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<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>
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</pre></div>
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</div>
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<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
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standard library distributed along with Python, and only by such
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modules (unverifiable). The use of <code class="docutils literal notranslate"><span class="pre">_log</span></code> 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:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">XXX</span><span class="p">:</span>
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<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>
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</pre></div>
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</div>
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<p>Then this class can create access methods to log to this private
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logger.</p>
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<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
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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>
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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>
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</section>
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<section id="module-list">
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<h2><a class="toc-backref" href="#module-list" role="doc-backlink">Module List</a></h2>
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<p>Here is a (possibly incomplete) list of modules to be reworked:</p>
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<ul class="simple">
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<li>asyncore (dispatcher.log, dispatcher.log_info)</li>
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<li>BaseHTTPServer (BaseHTTPRequestHandler.log_request,
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BaseHTTPRequestHandler.log_error,
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BaseHTTPRequestHandler.log_message)</li>
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<li>cgi (possibly - is cgi.log used by somebody?)</li>
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<li>ftplib (if FTP.debugging)</li>
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<li>gopherlib (get_directory)</li>
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<li>httplib (HTTPResponse, HTTPConnection)</li>
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<li>ihooks (_Verbose)</li>
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<li>imaplib (IMAP4._mesg)</li>
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<li>mhlib (MH.error)</li>
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<li>nntplib (NNTP)</li>
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<li>pipes (Template.makepipeline)</li>
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<li>pkgutil (extend_path)</li>
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<li>platform (_syscmd_ver)</li>
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<li>poplib (if POP3._debugging)</li>
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<li>profile (if Profile.verbose)</li>
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<li>robotparser (_debug)</li>
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<li>smtplib (if SGMLParser.verbose)</li>
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<li>shlex (if shlex.debug)</li>
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<li>smtpd (SMTPChannel/PureProxy where print >> DEBUGSTREAM)</li>
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<li>smtplib (if SMTP.debuglevel)</li>
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<li>SocketServer (BaseServer.handle_error)</li>
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<li>telnetlib (if Telnet.debuglevel)</li>
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<li>threading? (_Verbose._note, Thread.__bootstrap)</li>
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<li>timeit (Timer.print_exc)</li>
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<li>trace</li>
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<li>uu (decode)</li>
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</ul>
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<p>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:</p>
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<ul class="simple">
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<li>urllib</li>
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</ul>
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<p>Finally possibly some modules should be extended to provide more
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debug information.</p>
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</section>
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<section id="doubtful-modules">
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<h2><a class="toc-backref" href="#doubtful-modules" role="doc-backlink">Doubtful Modules</a></h2>
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<p>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.</p>
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<ul class="simple">
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<li>tabnanny (check)</li>
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</ul>
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</section>
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<section id="guidelines-for-logging-usage">
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<h2><a class="toc-backref" href="#guidelines-for-logging-usage" role="doc-backlink">Guidelines for Logging Usage</a></h2>
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<p>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 <code class="docutils literal notranslate"><span class="pre">__init__</span></code> module of the same sub-package will have the logger
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name “dummy.junk”.</p>
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</section>
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<section id="references">
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<h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2>
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<aside class="footnote-list brackets">
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<aside class="footnote brackets" id="id2" role="doc-footnote">
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<dt class="label" id="id2">[<a href="#id1">2</a>]</dt>
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<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>
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</aside>
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</section>
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<section id="copyright">
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||
<h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2>
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<p>This document has been placed in the public domain.</p>
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</section>
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</section>
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<hr class="docutils" />
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||
<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>
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<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0337.rst">2023-09-09 17:39:29 GMT</a></p>
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<h2>Contents</h2>
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<ul>
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<li><a class="reference internal" href="#abstract">Abstract</a></li>
|
||
<li><a class="reference internal" href="#pep-deferral">PEP Deferral</a></li>
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<li><a class="reference internal" href="#rationale">Rationale</a></li>
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<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>
|
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|
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<br>
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