<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-3052036-8']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 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Arbitrary levels are <em>not</em> supported. Note that when logging, you never need to refer to any level object; just use the methods on the log.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'You may not care'</span><span class="p">)</span> <span class="go">DEBUG:You may not care</span> <span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">'OMFG! Pants on fire!'</span><span class="p">)</span> <span class="go">ERROR:OMFG! Pants on fire!</span> </pre></div> </div> <p>The log can handle messages in several styles of <a class="reference internal" href="reference_guide.html#alternate-styles"><em>format strings</em></a>, defaulting to <a class="reference external" href="http://docs.python.org/library/string.html#format-string-syntax">new-style</a>.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'I wear {0} on my {where}'</span><span class="p">,</span> <span class="s">'pants'</span><span class="p">,</span> <span class="n">where</span><span class="o">=</span><span class="s">'legs'</span><span class="p">)</span> <span class="go">INFO:I wear pants on my legs</span> </pre></div> </div> <p>You can name your loggers.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">mylog</span> <span class="o">=</span> <span class="n">log</span><span class="o">.</span><span class="n">name</span><span class="p">(</span><span class="s">'alfredo'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">mylog</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'hello'</span><span class="p">)</span> <span class="go">DEBUG:alfredo:hello</span> </pre></div> </div> </div> <div class="section" id="better-output"> <span id="id1"></span><h2>Better output<a class="headerlink" href="#better-output" title="Permalink to this headline">¶</a></h2> <p>Twiggy’s default output strives to be user-friendly and to avoid pet peeves.</p> <p>Newlines are suppressed by default; that can be turned off per-message.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'user</span><span class="se">\n</span><span class="s">input</span><span class="se">\n</span><span class="s">annoys</span><span class="se">\n</span><span class="s">us'</span><span class="p">)</span> <span class="go">INFO:user\ninput\nannoys\nus</span> <span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">options</span><span class="p">(</span><span class="n">suppress_newlines</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'we</span><span class="se">\n</span><span class="s">deal'</span><span class="p">)</span> <span class="go">INFO:we</span> <span class="go">deal</span> </pre></div> </div> <p>Exceptions are prefixed by <tt class="docutils literal"><span class="pre">TRACE</span></tt>. By default, <a class="reference internal" href="api.html#twiggy.logger.BaseLogger.trace" title="twiggy.logger.BaseLogger.trace"><tt class="xref py py-meth docutils literal"><span class="pre">tracing</span></tt></a> will use the current exception, but you can also pass an exc_info tuple.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="k">try</span><span class="p">:</span> <span class="gp">... </span> <span class="mi">1</span><span class="o">/</span><span class="mi">0</span> <span class="gp">... </span><span class="k">except</span><span class="p">:</span> <span class="gp">... </span> <span class="n">log</span><span class="o">.</span><span class="n">trace</span><span class="p">(</span><span class="s">'error'</span><span class="p">)</span><span class="o">.</span><span class="n">warning</span><span class="p">(</span><span class="s">'oh noes'</span><span class="p">)</span> <span class="go">WARNING:oh noes</span> <span class="go">TRACE Traceback (most recent call last):</span> <span class="go">TRACE File "<doctest better-output[...]>", line 2, in <module></span> <span class="go">TRACE ZeroDivisionError: integer division or modulo by zero</span> </pre></div> </div> <div class="admonition-see-also admonition seealso"> <p class="first admonition-title">See also</p> <p class="last"><a class="reference internal" href="api.html#folding-exceptions"><em>How to fold exceptions to a single line</em></a></p> </div> </div> <div class="section" id="structured-logging"> <span id="id2"></span><h2>Structured Logging<a class="headerlink" href="#structured-logging" title="Permalink to this headline">¶</a></h2> <p>I like this method chaining style a lot.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">name</span><span class="p">(</span><span class="s">'benito'</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'hi there'</span><span class="p">)</span> <span class="go">INFO:benito:hi there</span> </pre></div> </div> <p>It makes <a class="reference internal" href="glossary.html#term-structured-logging"><em class="xref std std-term">structured logging</em></a> easy. In the past, fielded data was stuffed in the text of your message:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'Going for a walk. path: {0} roads: {1}'</span><span class="p">,</span> <span class="s">"less traveled"</span><span class="p">,</span> <span class="mi">42</span><span class="p">)</span> <span class="go">INFO:Going for a walk. path: less traveled roads: 42</span> </pre></div> </div> <p>Instead, you can use <a class="reference internal" href="api.html#twiggy.logger.BaseLogger.fields" title="twiggy.logger.BaseLogger.fields"><tt class="xref py py-meth docutils literal"><span class="pre">fields()</span></tt></a> to add arbitrary key-value pairs. Output is easily parseable.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">path</span><span class="o">=</span><span class="s">"less traveled"</span><span class="p">,</span> <span class="n">roads</span><span class="o">=</span><span class="mi">42</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'Going for a walk'</span><span class="p">)</span> <span class="go">INFO:path=less traveled:roads=42:Going for a walk</span> </pre></div> </div> <p>The <a class="reference internal" href="api.html#twiggy.logger.BaseLogger.struct" title="twiggy.logger.BaseLogger.struct"><tt class="xref py py-meth docutils literal"><span class="pre">struct()</span></tt></a> is a short cut for <em>only</em> logging fields. This is great for runtime statistics gathering.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">struct</span><span class="p">(</span><span class="n">paths</span><span class="o">=</span><span class="mi">42</span><span class="p">,</span> <span class="n">dolphins</span><span class="o">=</span><span class="s">'thankful'</span><span class="p">)</span> <span class="go">INFO:dolphins=thankful:paths=42:</span> </pre></div> </div> </div> <div class="section" id="partial-binding"> <h2>Partial Binding<a class="headerlink" href="#partial-binding" title="Permalink to this headline">¶</a></h2> <p>Each call to <a class="reference internal" href="api.html#twiggy.logger.BaseLogger.fields" title="twiggy.logger.BaseLogger.fields"><tt class="xref py py-meth docutils literal"><span class="pre">fields()</span></tt></a> or <a class="reference internal" href="api.html#twiggy.logger.BaseLogger.options" title="twiggy.logger.BaseLogger.options"><tt class="xref py py-meth docutils literal"><span class="pre">options()</span></tt></a> creates a new, independent log instance that inherits all of the data of the parent. This incremental binding can be useful for webapps.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="c">## an application-level log</span> <span class="gp">... </span><span class="n">webapp_log</span> <span class="o">=</span> <span class="n">log</span><span class="o">.</span><span class="n">name</span><span class="p">(</span><span class="s">"myblog"</span><span class="p">)</span> <span class="gp">>>> </span><span class="c">## a log for the individual request</span> <span class="gp">... </span><span class="n">current_request_log</span> <span class="o">=</span> <span class="n">webapp_log</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">request_id</span><span class="o">=</span><span class="s">'12345'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">current_request_log</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">rows</span><span class="o">=</span><span class="mi">100</span><span class="p">,</span> <span class="n">user</span><span class="o">=</span><span class="s">'frank'</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'frobnicating database'</span><span class="p">)</span> <span class="go">INFO:myblog:request_id=12345:rows=100:user=frank:frobnicating database</span> <span class="gp">>>> </span><span class="n">current_request_log</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="nb">bytes</span><span class="o">=</span><span class="mi">5678</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'sending page over tubes'</span><span class="p">)</span> <span class="go">INFO:myblog:bytes=5678:request_id=12345:sending page over tubes</span> <span class="gp">>>> </span><span class="c">## a log for a different request</span> <span class="gp">... </span><span class="n">another_log</span> <span class="o">=</span> <span class="n">webapp_log</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">request_id</span><span class="o">=</span><span class="s">'67890'</span><span class="p">)</span> <span class="gp">>>> </span><span class="n">another_log</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'Client connected'</span><span class="p">)</span> <span class="go">DEBUG:myblog:request_id=67890:Client connected</span> </pre></div> </div> <p>Chained style is awesome. It allows you to create complex yet parsable log messages in a concise way.</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log</span><span class="o">.</span><span class="n">name</span><span class="p">(</span><span class="s">'donjuan'</span><span class="p">)</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">pants</span><span class="o">=</span><span class="s">'sexy'</span><span class="p">)</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">"hello, {who} want to {what}?"</span><span class="p">,</span> <span class="n">who</span><span class="o">=</span><span class="s">'ladies'</span><span class="p">,</span> <span class="n">what</span><span class="o">=</span><span class="s">'dance'</span><span class="p">)</span> <span class="go">INFO:donjuan:pants=sexy:hello, ladies want to dance?</span> </pre></div> </div> </div> <div class="section" id="sample-output"> <h2>Sample Output<a class="headerlink" href="#sample-output" title="Permalink to this headline">¶</a></h2> <p id="sample-file-output">Routed to a <a class="reference internal" href="api.html#twiggy.outputs.FileOutput" title="twiggy.outputs.FileOutput"><tt class="xref py py-obj docutils literal"><span class="pre">file</span></tt></a>, the above produces the following:</p> <div class="highlight-python"><pre>2010-03-28T14:23:34Z:DEBUG:You may not care 2010-03-28T14:23:34Z:ERROR:OMFG! Pants on fire! 2010-03-28T14:23:34Z:INFO:I like bikes 2010-03-28T14:23:34Z:INFO:I wear pants on my legs 2010-03-28T14:23:34Z:DEBUG:alfredo:hello 2010-03-28T14:23:34Z:INFO:user\ninput\nannoys\nus 2010-03-28T14:23:34Z:INFO:we deal 2010-03-28T14:23:34Z:WARNING:oh noes TRACE Traceback (most recent call last): TRACE File "<doctest better-output[...]>", line 35, in <module> TRACE ZeroDivisionError: integer division or modulo by zero 2010-03-28T14:23:34Z:INFO:benito:hi there 2010-03-28T14:23:34Z:INFO:Going for a walk. path: less traveled roads: 42 2010-03-28T14:23:34Z:INFO:path=less traveled:roads=42:Going for a walk 2010-03-28T14:23:34Z:INFO:dolphins=thankful:paths=42: 2010-03-28T14:23:34Z:INFO:myblog:request_id=12345:rows=100:user=frank:frobnicating database 2010-03-28T14:23:34Z:INFO:myblog:bytes=5678:request_id=12345:sending page over tubes 2010-03-28T14:23:34Z:INFO:myblog:request_id=67890:Client connected 2010-03-28T14:23:34Z:INFO:donjuan:pants=sexy:hello, ladies want to dance? 2010-03-28T14:23:34Z:INFO:myblog:request_id=12345:rows=100:user=frank:frobnicating database 2010-03-28T14:23:34Z:INFO:myblog:bytes=5678:request_id=12345:sending page over tubes 2010-03-28T14:23:34Z:DEBUG:myblog:request_id=67890:Client connected</pre> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <p class="logo"><a href="index.html"> <img class="logo" src="_static/twig_sidebar.jpg" alt="Logo"/> </a></p> <h3><a href="index.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">Logging Messages</a><ul> <li><a class="reference internal" href="#the-magic-log">The Magic log</a></li> <li><a class="reference internal" href="#better-output">Better output</a></li> <li><a class="reference internal" href="#structured-logging">Structured Logging</a></li> <li><a class="reference internal" href="#partial-binding">Partial Binding</a></li> <li><a class="reference internal" href="#sample-output">Sample Output</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="index.html" title="previous chapter">Twiggy: A Pythonic Logger</a></p> <h4>Next topic</h4> <p class="topless"><a href="configuration.html" title="next chapter">Configuring Output</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="_sources/logging.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="search.html" method="get"> <input type="text" name="q" size="18" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="configuration.html" title="Configuring Output" >next</a> |</li> <li class="right" > <a href="index.html" title="Twiggy: A Pythonic Logger" >previous</a> |</li> <li><a href="index.html">Twiggy v0.4.4 documentation</a> »</li> </ul> </div> <div class="footer"> © Copyright 2010, <a href="http://i.wearpants.org">Peter Fein</a>. 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