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<div class="section" id="logging-cookbook">
<span id="id1"></span><h1>Logging Cookbook<a class="headerlink" href="#logging-cookbook" title="Permalink to this headline">¶</a></h1>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Author:</th><td class="field-body">Vinay Sajip <vinay_sajip at red-dove dot com></td>
</tr>
</tbody>
</table>
<p>This page contains a number of recipes related to logging, which have been found
useful in the past.</p>
<div class="section" id="using-logging-in-multiple-modules">
<h2>Using logging in multiple modules<a class="headerlink" href="#using-logging-in-multiple-modules" title="Permalink to this headline">¶</a></h2>
<p>Multiple calls to <tt class="docutils literal"><span class="pre">logging.getLogger('someLogger')</span></tt> return a reference to the
same logger object. This is true not only within the same module, but also
across modules as long as it is in the same Python interpreter process. It is
true for references to the same object; additionally, application code can
define and configure a parent logger in one module and create (but not
configure) a child logger in a separate module, and all logger calls to the
child will pass up to the parent. Here is a main module:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">auxiliary_module</span>
<span class="c"># create logger with 'spam_application'</span>
<span class="n">logger</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="s">'spam_application'</span><span class="p">)</span>
<span class="n">logger</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">DEBUG</span><span class="p">)</span>
<span class="c"># create file handler which logs even debug messages</span>
<span class="n">fh</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">FileHandler</span><span class="p">(</span><span class="s">'spam.log'</span><span class="p">)</span>
<span class="n">fh</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">DEBUG</span><span class="p">)</span>
<span class="c"># create console handler with a higher log level</span>
<span class="n">ch</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">StreamHandler</span><span class="p">()</span>
<span class="n">ch</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">ERROR</span><span class="p">)</span>
<span class="c"># create formatter and add it to the handlers</span>
<span class="n">formatter</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">Formatter</span><span class="p">(</span><span class="s">'%(asctime)s - %(name)s - %(levelname)s - %(message)s'</span><span class="p">)</span>
<span class="n">fh</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="n">ch</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="c"># add the handlers to the logger</span>
<span class="n">logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">fh</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">ch</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'creating an instance of auxiliary_module.Auxiliary'</span><span class="p">)</span>
<span class="n">a</span> <span class="o">=</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">Auxiliary</span><span class="p">()</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'created an instance of auxiliary_module.Auxiliary'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'calling auxiliary_module.Auxiliary.do_something'</span><span class="p">)</span>
<span class="n">a</span><span class="o">.</span><span class="n">do_something</span><span class="p">()</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'finished auxiliary_module.Auxiliary.do_something'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'calling auxiliary_module.some_function()'</span><span class="p">)</span>
<span class="n">auxiliary_module</span><span class="o">.</span><span class="n">some_function</span><span class="p">()</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'done with auxiliary_module.some_function()'</span><span class="p">)</span>
</pre></div>
</div>
<p>Here is the auxiliary module:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="c"># create logger</span>
<span class="n">module_logger</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="s">'spam_application.auxiliary'</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Auxiliary</span><span class="p">:</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logger</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="s">'spam_application.auxiliary.Auxiliary'</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'creating an instance of Auxiliary'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">do_something</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'doing something'</span><span class="p">)</span>
<span class="n">a</span> <span class="o">=</span> <span class="mi">1</span> <span class="o">+</span> <span class="mi">1</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'done doing something'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">some_function</span><span class="p">():</span>
<span class="n">module_logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'received a call to "some_function"'</span><span class="p">)</span>
</pre></div>
</div>
<p>The output looks like this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">663</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">creating</span> <span class="n">an</span> <span class="n">instance</span> <span class="n">of</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">Auxiliary</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">665</span> <span class="o">-</span> <span class="n">spam_application</span><span class="o">.</span><span class="n">auxiliary</span><span class="o">.</span><span class="n">Auxiliary</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">creating</span> <span class="n">an</span> <span class="n">instance</span> <span class="n">of</span> <span class="n">Auxiliary</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">665</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">created</span> <span class="n">an</span> <span class="n">instance</span> <span class="n">of</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">Auxiliary</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">668</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">calling</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">Auxiliary</span><span class="o">.</span><span class="n">do_something</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">668</span> <span class="o">-</span> <span class="n">spam_application</span><span class="o">.</span><span class="n">auxiliary</span><span class="o">.</span><span class="n">Auxiliary</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">doing</span> <span class="n">something</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">669</span> <span class="o">-</span> <span class="n">spam_application</span><span class="o">.</span><span class="n">auxiliary</span><span class="o">.</span><span class="n">Auxiliary</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">done</span> <span class="n">doing</span> <span class="n">something</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">670</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">finished</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">Auxiliary</span><span class="o">.</span><span class="n">do_something</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">671</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">calling</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">some_function</span><span class="p">()</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">672</span> <span class="o">-</span> <span class="n">spam_application</span><span class="o">.</span><span class="n">auxiliary</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">received</span> <span class="n">a</span> <span class="n">call</span> <span class="n">to</span> <span class="s">'some_function'</span>
<span class="mi">2005</span><span class="o">-</span><span class="mi">03</span><span class="o">-</span><span class="mi">23</span> <span class="mi">23</span><span class="p">:</span><span class="mi">47</span><span class="p">:</span><span class="mi">11</span><span class="p">,</span><span class="mi">673</span> <span class="o">-</span> <span class="n">spam_application</span> <span class="o">-</span> <span class="n">INFO</span> <span class="o">-</span>
<span class="n">done</span> <span class="k">with</span> <span class="n">auxiliary_module</span><span class="o">.</span><span class="n">some_function</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="multiple-handlers-and-formatters">
<h2>Multiple handlers and formatters<a class="headerlink" href="#multiple-handlers-and-formatters" title="Permalink to this headline">¶</a></h2>
<p>Loggers are plain Python objects. The <tt class="xref py py-func docutils literal"><span class="pre">addHandler()</span></tt> method has no minimum
or maximum quota for the number of handlers you may add. Sometimes it will be
beneficial for an application to log all messages of all severities to a text
file while simultaneously logging errors or above to the console. To set this
up, simply configure the appropriate handlers. The logging calls in the
application code will remain unchanged. Here is a slight modification to the
previous simple module-based configuration example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="n">logger</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="s">'simple_example'</span><span class="p">)</span>
<span class="n">logger</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">DEBUG</span><span class="p">)</span>
<span class="c"># create file handler which logs even debug messages</span>
<span class="n">fh</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">FileHandler</span><span class="p">(</span><span class="s">'spam.log'</span><span class="p">)</span>
<span class="n">fh</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">DEBUG</span><span class="p">)</span>
<span class="c"># create console handler with a higher log level</span>
<span class="n">ch</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">StreamHandler</span><span class="p">()</span>
<span class="n">ch</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">ERROR</span><span class="p">)</span>
<span class="c"># create formatter and add it to the handlers</span>
<span class="n">formatter</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">Formatter</span><span class="p">(</span><span class="s">'%(asctime)s - %(name)s - %(levelname)s - %(message)s'</span><span class="p">)</span>
<span class="n">ch</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="n">fh</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="c"># add the handlers to logger</span>
<span class="n">logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">ch</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">fh</span><span class="p">)</span>
<span class="c"># 'application' code</span>
<span class="n">logger</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'debug message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'info message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s">'warn message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">'error message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">critical</span><span class="p">(</span><span class="s">'critical message'</span><span class="p">)</span>
</pre></div>
</div>
<p>Notice that the ‘application’ code does not care about multiple handlers. All
that changed was the addition and configuration of a new handler named <em>fh</em>.</p>
<p>The ability to create new handlers with higher- or lower-severity filters can be
very helpful when writing and testing an application. Instead of using many
<tt class="docutils literal"><span class="pre">print</span></tt> statements for debugging, use <tt class="docutils literal"><span class="pre">logger.debug</span></tt>: Unlike the print
statements, which you will have to delete or comment out later, the logger.debug
statements can remain intact in the source code and remain dormant until you
need them again. At that time, the only change that needs to happen is to
modify the severity level of the logger and/or handler to debug.</p>
</div>
<div class="section" id="logging-to-multiple-destinations">
<span id="multiple-destinations"></span><h2>Logging to multiple destinations<a class="headerlink" href="#logging-to-multiple-destinations" title="Permalink to this headline">¶</a></h2>
<p>Let’s say you want to log to console and file with different message formats and
in differing circumstances. Say you want to log messages with levels of DEBUG
and higher to file, and those messages at level INFO and higher to the console.
Let’s also assume that the file should contain timestamps, but the console
messages should not. Here’s how you can achieve this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="c"># set up logging to file - see previous section for more details</span>
<span class="n">logging</span><span class="o">.</span><span class="n">basicConfig</span><span class="p">(</span><span class="n">level</span><span class="o">=</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span>
<span class="nb">format</span><span class="o">=</span><span class="s">'%(asctime)s %(name)-12s %(levelname)-8s %(message)s'</span><span class="p">,</span>
<span class="n">datefmt</span><span class="o">=</span><span class="s">'%m-%d %H:%M'</span><span class="p">,</span>
<span class="n">filename</span><span class="o">=</span><span class="s">'/temp/myapp.log'</span><span class="p">,</span>
<span class="n">filemode</span><span class="o">=</span><span class="s">'w'</span><span class="p">)</span>
<span class="c"># define a Handler which writes INFO messages or higher to the sys.stderr</span>
<span class="n">console</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">StreamHandler</span><span class="p">()</span>
<span class="n">console</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">INFO</span><span class="p">)</span>
<span class="c"># set a format which is simpler for console use</span>
<span class="n">formatter</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">Formatter</span><span class="p">(</span><span class="s">'%(name)-12s: %(levelname)-8s %(message)s'</span><span class="p">)</span>
<span class="c"># tell the handler to use this format</span>
<span class="n">console</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="c"># add the handler to the root logger</span>
<span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s">''</span><span class="p">)</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">console</span><span class="p">)</span>
<span class="c"># Now, we can log to the root logger, or any other logger. First the root...</span>
<span class="n">logging</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'Jackdaws love my big sphinx of quartz.'</span><span class="p">)</span>
<span class="c"># Now, define a couple of other loggers which might represent areas in your</span>
<span class="c"># application:</span>
<span class="n">logger1</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="s">'myapp.area1'</span><span class="p">)</span>
<span class="n">logger2</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="s">'myapp.area2'</span><span class="p">)</span>
<span class="n">logger1</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'Quick zephyrs blow, vexing daft Jim.'</span><span class="p">)</span>
<span class="n">logger1</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'How quickly daft jumping zebras vex.'</span><span class="p">)</span>
<span class="n">logger2</span><span class="o">.</span><span class="n">warning</span><span class="p">(</span><span class="s">'Jail zesty vixen who grabbed pay from quack.'</span><span class="p">)</span>
<span class="n">logger2</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">'The five boxing wizards jump quickly.'</span><span class="p">)</span>
</pre></div>
</div>
<p>When you run this, on the console you will see</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">root</span> <span class="p">:</span> <span class="n">INFO</span> <span class="n">Jackdaws</span> <span class="n">love</span> <span class="n">my</span> <span class="n">big</span> <span class="n">sphinx</span> <span class="n">of</span> <span class="n">quartz</span><span class="o">.</span>
<span class="n">myapp</span><span class="o">.</span><span class="n">area1</span> <span class="p">:</span> <span class="n">INFO</span> <span class="n">How</span> <span class="n">quickly</span> <span class="n">daft</span> <span class="n">jumping</span> <span class="n">zebras</span> <span class="n">vex</span><span class="o">.</span>
<span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="p">:</span> <span class="n">WARNING</span> <span class="n">Jail</span> <span class="n">zesty</span> <span class="n">vixen</span> <span class="n">who</span> <span class="n">grabbed</span> <span class="n">pay</span> <span class="kn">from</span> <span class="nn">quack.</span>
<span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="p">:</span> <span class="n">ERROR</span> <span class="n">The</span> <span class="n">five</span> <span class="n">boxing</span> <span class="n">wizards</span> <span class="n">jump</span> <span class="n">quickly</span><span class="o">.</span>
</pre></div>
</div>
<p>and in the file you will see something like</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="mi">10</span><span class="o">-</span><span class="mi">22</span> <span class="mi">22</span><span class="p">:</span><span class="mi">19</span> <span class="n">root</span> <span class="n">INFO</span> <span class="n">Jackdaws</span> <span class="n">love</span> <span class="n">my</span> <span class="n">big</span> <span class="n">sphinx</span> <span class="n">of</span> <span class="n">quartz</span><span class="o">.</span>
<span class="mi">10</span><span class="o">-</span><span class="mi">22</span> <span class="mi">22</span><span class="p">:</span><span class="mi">19</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area1</span> <span class="n">DEBUG</span> <span class="n">Quick</span> <span class="n">zephyrs</span> <span class="n">blow</span><span class="p">,</span> <span class="n">vexing</span> <span class="n">daft</span> <span class="n">Jim</span><span class="o">.</span>
<span class="mi">10</span><span class="o">-</span><span class="mi">22</span> <span class="mi">22</span><span class="p">:</span><span class="mi">19</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area1</span> <span class="n">INFO</span> <span class="n">How</span> <span class="n">quickly</span> <span class="n">daft</span> <span class="n">jumping</span> <span class="n">zebras</span> <span class="n">vex</span><span class="o">.</span>
<span class="mi">10</span><span class="o">-</span><span class="mi">22</span> <span class="mi">22</span><span class="p">:</span><span class="mi">19</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="n">WARNING</span> <span class="n">Jail</span> <span class="n">zesty</span> <span class="n">vixen</span> <span class="n">who</span> <span class="n">grabbed</span> <span class="n">pay</span> <span class="kn">from</span> <span class="nn">quack.</span>
<span class="mi">10</span><span class="o">-</span><span class="mi">22</span> <span class="mi">22</span><span class="p">:</span><span class="mi">19</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="n">ERROR</span> <span class="n">The</span> <span class="n">five</span> <span class="n">boxing</span> <span class="n">wizards</span> <span class="n">jump</span> <span class="n">quickly</span><span class="o">.</span>
</pre></div>
</div>
<p>As you can see, the DEBUG message only shows up in the file. The other messages
are sent to both destinations.</p>
<p>This example uses console and file handlers, but you can use any number and
combination of handlers you choose.</p>
</div>
<div class="section" id="configuration-server-example">
<h2>Configuration server example<a class="headerlink" href="#configuration-server-example" title="Permalink to this headline">¶</a></h2>
<p>Here is an example of a module using the logging configuration server:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">logging.config</span>
<span class="kn">import</span> <span class="nn">time</span>
<span class="kn">import</span> <span class="nn">os</span>
<span class="c"># read initial config file</span>
<span class="n">logging</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">fileConfig</span><span class="p">(</span><span class="s">'logging.conf'</span><span class="p">)</span>
<span class="c"># create and start listener on port 9999</span>
<span class="n">t</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="mi">9999</span><span class="p">)</span>
<span class="n">t</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">logger</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="s">'simpleExample'</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="c"># loop through logging calls to see the difference</span>
<span class="c"># new configurations make, until Ctrl+C is pressed</span>
<span class="k">while</span> <span class="k">True</span><span class="p">:</span>
<span class="n">logger</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'debug message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'info message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="s">'warn message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">'error message'</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">critical</span><span class="p">(</span><span class="s">'critical message'</span><span class="p">)</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">KeyboardInterrupt</span><span class="p">:</span>
<span class="c"># cleanup</span>
<span class="n">logging</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">stopListening</span><span class="p">()</span>
<span class="n">t</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
</pre></div>
</div>
<p>And here is a script that takes a filename and sends that file to the server,
properly preceded with the binary-encoded length, as the new logging
configuration:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="c">#!/usr/bin/env python</span>
<span class="kn">import</span> <span class="nn">socket</span><span class="o">,</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">struct</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="s">'rb'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">data_to_send</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="n">HOST</span> <span class="o">=</span> <span class="s">'localhost'</span>
<span class="n">PORT</span> <span class="o">=</span> <span class="mi">9999</span>
<span class="n">s</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">(</span><span class="n">socket</span><span class="o">.</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">socket</span><span class="o">.</span><span class="n">SOCK_STREAM</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'connecting...'</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">connect</span><span class="p">((</span><span class="n">HOST</span><span class="p">,</span> <span class="n">PORT</span><span class="p">))</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'sending config...'</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">struct</span><span class="o">.</span><span class="n">pack</span><span class="p">(</span><span class="s">'>L'</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">data_to_send</span><span class="p">)))</span>
<span class="n">s</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data_to_send</span><span class="p">)</span>
<span class="n">s</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'complete'</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="dealing-with-handlers-that-block">
<h2>Dealing with handlers that block<a class="headerlink" href="#dealing-with-handlers-that-block" title="Permalink to this headline">¶</a></h2>
<p>Sometimes you have to get your logging handlers to do their work without
blocking the thread you’re logging from. This is common in Web applications,
though of course it also occurs in other scenarios.</p>
<p>A common culprit which demonstrates sluggish behaviour is the
<a class="reference internal" href="../library/logging.handlers.html#logging.handlers.SMTPHandler" title="logging.handlers.SMTPHandler"><tt class="xref py py-class docutils literal"><span class="pre">SMTPHandler</span></tt></a>: sending emails can take a long time, for a
number of reasons outside the developer’s control (for example, a poorly
performing mail or network infrastructure). But almost any network-based
handler can block: Even a <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.SocketHandler" title="logging.handlers.SocketHandler"><tt class="xref py py-class docutils literal"><span class="pre">SocketHandler</span></tt></a> operation may do a
DNS query under the hood which is too slow (and this query can be deep in the
socket library code, below the Python layer, and outside your control).</p>
<p>One solution is to use a two-part approach. For the first part, attach only a
<a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueHandler" title="logging.handlers.QueueHandler"><tt class="xref py py-class docutils literal"><span class="pre">QueueHandler</span></tt></a> to those loggers which are accessed from
performance-critical threads. They simply write to their queue, which can be
sized to a large enough capacity or initialized with no upper bound to their
size. The write to the queue will typically be accepted quickly, though you
will probably need to catch the <a class="reference internal" href="../library/queue.html#queue.Full" title="queue.Full"><tt class="xref py py-exc docutils literal"><span class="pre">queue.Full</span></tt></a> exception as a precaution
in your code. If you are a library developer who has performance-critical
threads in their code, be sure to document this (together with a suggestion to
attach only <tt class="docutils literal"><span class="pre">QueueHandlers</span></tt> to your loggers) for the benefit of other
developers who will use your code.</p>
<p>The second part of the solution is <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueListener" title="logging.handlers.QueueListener"><tt class="xref py py-class docutils literal"><span class="pre">QueueListener</span></tt></a>, which has been
designed as the counterpart to <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueHandler" title="logging.handlers.QueueHandler"><tt class="xref py py-class docutils literal"><span class="pre">QueueHandler</span></tt></a>. A
<a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueListener" title="logging.handlers.QueueListener"><tt class="xref py py-class docutils literal"><span class="pre">QueueListener</span></tt></a> is very simple: it’s passed a queue and some handlers,
and it fires up an internal thread which listens to its queue for LogRecords
sent from <tt class="docutils literal"><span class="pre">QueueHandlers</span></tt> (or any other source of <tt class="docutils literal"><span class="pre">LogRecords</span></tt>, for that
matter). The <tt class="docutils literal"><span class="pre">LogRecords</span></tt> are removed from the queue and passed to the
handlers for processing.</p>
<p>The advantage of having a separate <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueListener" title="logging.handlers.QueueListener"><tt class="xref py py-class docutils literal"><span class="pre">QueueListener</span></tt></a> class is that you
can use the same instance to service multiple <tt class="docutils literal"><span class="pre">QueueHandlers</span></tt>. This is more
resource-friendly than, say, having threaded versions of the existing handler
classes, which would eat up one thread per handler for no particular benefit.</p>
<p>An example of using these two classes follows (imports omitted):</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">que</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">Queue</span><span class="p">(</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="c"># no limit on size</span>
<span class="n">queue_handler</span> <span class="o">=</span> <span class="n">QueueHandler</span><span class="p">(</span><span class="n">que</span><span class="p">)</span>
<span class="n">handler</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">StreamHandler</span><span class="p">()</span>
<span class="n">listener</span> <span class="o">=</span> <span class="n">QueueListener</span><span class="p">(</span><span class="n">que</span><span class="p">,</span> <span class="n">handler</span><span class="p">)</span>
<span class="n">root</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="n">root</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">queue_handler</span><span class="p">)</span>
<span class="n">formatter</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">Formatter</span><span class="p">(</span><span class="s">'%(threadName)s: %(message)s'</span><span class="p">)</span>
<span class="n">handler</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">formatter</span><span class="p">)</span>
<span class="n">listener</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="c"># The log output will display the thread which generated</span>
<span class="c"># the event (the main thread) rather than the internal</span>
<span class="c"># thread which monitors the internal queue. This is what</span>
<span class="c"># you want to happen.</span>
<span class="n">root</span><span class="o">.</span><span class="n">warning</span><span class="p">(</span><span class="s">'Look out!'</span><span class="p">)</span>
<span class="n">listener</span><span class="o">.</span><span class="n">stop</span><span class="p">()</span>
</pre></div>
</div>
<p>which, when run, will produce:</p>
<div class="highlight-python3"><pre>MainThread: Look out!</pre>
</div>
</div>
<div class="section" id="sending-and-receiving-logging-events-across-a-network">
<span id="network-logging"></span><h2>Sending and receiving logging events across a network<a class="headerlink" href="#sending-and-receiving-logging-events-across-a-network" title="Permalink to this headline">¶</a></h2>
<p>Let’s say you want to send logging events across a network, and handle them at
the receiving end. A simple way of doing this is attaching a
<a class="reference internal" href="../library/logging.handlers.html#logging.handlers.SocketHandler" title="logging.handlers.SocketHandler"><tt class="xref py py-class docutils literal"><span class="pre">SocketHandler</span></tt></a> instance to the root logger at the sending end:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span><span class="o">,</span> <span class="nn">logging.handlers</span>
<span class="n">rootLogger</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="s">''</span><span class="p">)</span>
<span class="n">rootLogger</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">DEBUG</span><span class="p">)</span>
<span class="n">socketHandler</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">SocketHandler</span><span class="p">(</span><span class="s">'localhost'</span><span class="p">,</span>
<span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">DEFAULT_TCP_LOGGING_PORT</span><span class="p">)</span>
<span class="c"># don't bother with a formatter, since a socket handler sends the event as</span>
<span class="c"># an unformatted pickle</span>
<span class="n">rootLogger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">socketHandler</span><span class="p">)</span>
<span class="c"># Now, we can log to the root logger, or any other logger. First the root...</span>
<span class="n">logging</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'Jackdaws love my big sphinx of quartz.'</span><span class="p">)</span>
<span class="c"># Now, define a couple of other loggers which might represent areas in your</span>
<span class="c"># application:</span>
<span class="n">logger1</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="s">'myapp.area1'</span><span class="p">)</span>
<span class="n">logger2</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="s">'myapp.area2'</span><span class="p">)</span>
<span class="n">logger1</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'Quick zephyrs blow, vexing daft Jim.'</span><span class="p">)</span>
<span class="n">logger1</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'How quickly daft jumping zebras vex.'</span><span class="p">)</span>
<span class="n">logger2</span><span class="o">.</span><span class="n">warning</span><span class="p">(</span><span class="s">'Jail zesty vixen who grabbed pay from quack.'</span><span class="p">)</span>
<span class="n">logger2</span><span class="o">.</span><span class="n">error</span><span class="p">(</span><span class="s">'The five boxing wizards jump quickly.'</span><span class="p">)</span>
</pre></div>
</div>
<p>At the receiving end, you can set up a receiver using the <a class="reference internal" href="../library/socketserver.html#module-socketserver" title="socketserver: A framework for network servers."><tt class="xref py py-mod docutils literal"><span class="pre">socketserver</span></tt></a>
module. Here is a basic working example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">pickle</span>
<span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">logging.handlers</span>
<span class="kn">import</span> <span class="nn">socketserver</span>
<span class="kn">import</span> <span class="nn">struct</span>
<span class="k">class</span> <span class="nc">LogRecordStreamHandler</span><span class="p">(</span><span class="n">socketserver</span><span class="o">.</span><span class="n">StreamRequestHandler</span><span class="p">):</span>
<span class="sd">"""Handler for a streaming logging request.</span>
<span class="sd"> This basically logs the record using whatever logging policy is</span>
<span class="sd"> configured locally.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">handle</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> Handle multiple requests - each expected to be a 4-byte length,</span>
<span class="sd"> followed by the LogRecord in pickle format. Logs the record</span>
<span class="sd"> according to whatever policy is configured locally.</span>
<span class="sd"> """</span>
<span class="k">while</span> <span class="k">True</span><span class="p">:</span>
<span class="n">chunk</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span> <span class="o"><</span> <span class="mi">4</span><span class="p">:</span>
<span class="k">break</span>
<span class="n">slen</span> <span class="o">=</span> <span class="n">struct</span><span class="o">.</span><span class="n">unpack</span><span class="p">(</span><span class="s">'>L'</span><span class="p">,</span> <span class="n">chunk</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span>
<span class="n">chunk</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="n">slen</span><span class="p">)</span>
<span class="k">while</span> <span class="nb">len</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span> <span class="o"><</span> <span class="n">slen</span><span class="p">:</span>
<span class="n">chunk</span> <span class="o">=</span> <span class="n">chunk</span> <span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">connection</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="n">slen</span> <span class="o">-</span> <span class="nb">len</span><span class="p">(</span><span class="n">chunk</span><span class="p">))</span>
<span class="n">obj</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">unPickle</span><span class="p">(</span><span class="n">chunk</span><span class="p">)</span>
<span class="n">record</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">makeLogRecord</span><span class="p">(</span><span class="n">obj</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">handleLogRecord</span><span class="p">(</span><span class="n">record</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">unPickle</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
<span class="k">return</span> <span class="n">pickle</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">handleLogRecord</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">record</span><span class="p">):</span>
<span class="c"># if a name is specified, we use the named logger rather than the one</span>
<span class="c"># implied by the record.</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">server</span><span class="o">.</span><span class="n">logname</span> <span class="ow">is</span> <span class="ow">not</span> <span class="k">None</span><span class="p">:</span>
<span class="n">name</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">server</span><span class="o">.</span><span class="n">logname</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">record</span><span class="o">.</span><span class="n">name</span>
<span class="n">logger</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="n">name</span><span class="p">)</span>
<span class="c"># N.B. EVERY record gets logged. This is because Logger.handle</span>
<span class="c"># is normally called AFTER logger-level filtering. If you want</span>
<span class="c"># to do filtering, do it at the client end to save wasting</span>
<span class="c"># cycles and network bandwidth!</span>
<span class="n">logger</span><span class="o">.</span><span class="n">handle</span><span class="p">(</span><span class="n">record</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">LogRecordSocketReceiver</span><span class="p">(</span><span class="n">socketserver</span><span class="o">.</span><span class="n">ThreadingTCPServer</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> Simple TCP socket-based logging receiver suitable for testing.</span>
<span class="sd"> """</span>
<span class="n">allow_reuse_address</span> <span class="o">=</span> <span class="mi">1</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">host</span><span class="o">=</span><span class="s">'localhost'</span><span class="p">,</span>
<span class="n">port</span><span class="o">=</span><span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">DEFAULT_TCP_LOGGING_PORT</span><span class="p">,</span>
<span class="n">handler</span><span class="o">=</span><span class="n">LogRecordStreamHandler</span><span class="p">):</span>
<span class="n">socketserver</span><span class="o">.</span><span class="n">ThreadingTCPServer</span><span class="o">.</span><span class="n">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="p">(</span><span class="n">host</span><span class="p">,</span> <span class="n">port</span><span class="p">),</span> <span class="n">handler</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">abort</span> <span class="o">=</span> <span class="mi">0</span>
<span class="bp">self</span><span class="o">.</span><span class="n">timeout</span> <span class="o">=</span> <span class="mi">1</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logname</span> <span class="o">=</span> <span class="k">None</span>
<span class="k">def</span> <span class="nf">serve_until_stopped</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="kn">import</span> <span class="nn">select</span>
<span class="n">abort</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">while</span> <span class="ow">not</span> <span class="n">abort</span><span class="p">:</span>
<span class="n">rd</span><span class="p">,</span> <span class="n">wr</span><span class="p">,</span> <span class="n">ex</span> <span class="o">=</span> <span class="n">select</span><span class="o">.</span><span class="n">select</span><span class="p">([</span><span class="bp">self</span><span class="o">.</span><span class="n">socket</span><span class="o">.</span><span class="n">fileno</span><span class="p">()],</span>
<span class="p">[],</span> <span class="p">[],</span>
<span class="bp">self</span><span class="o">.</span><span class="n">timeout</span><span class="p">)</span>
<span class="k">if</span> <span class="n">rd</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">handle_request</span><span class="p">()</span>
<span class="n">abort</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">abort</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="n">logging</span><span class="o">.</span><span class="n">basicConfig</span><span class="p">(</span>
<span class="nb">format</span><span class="o">=</span><span class="s">'%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s'</span><span class="p">)</span>
<span class="n">tcpserver</span> <span class="o">=</span> <span class="n">LogRecordSocketReceiver</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'About to start TCP server...'</span><span class="p">)</span>
<span class="n">tcpserver</span><span class="o">.</span><span class="n">serve_until_stopped</span><span class="p">()</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>First run the server, and then the client. On the client side, nothing is
printed on the console; on the server side, you should see something like:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">About</span> <span class="n">to</span> <span class="n">start</span> <span class="n">TCP</span> <span class="n">server</span><span class="o">...</span>
<span class="mi">59</span> <span class="n">root</span> <span class="n">INFO</span> <span class="n">Jackdaws</span> <span class="n">love</span> <span class="n">my</span> <span class="n">big</span> <span class="n">sphinx</span> <span class="n">of</span> <span class="n">quartz</span><span class="o">.</span>
<span class="mi">59</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area1</span> <span class="n">DEBUG</span> <span class="n">Quick</span> <span class="n">zephyrs</span> <span class="n">blow</span><span class="p">,</span> <span class="n">vexing</span> <span class="n">daft</span> <span class="n">Jim</span><span class="o">.</span>
<span class="mi">69</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area1</span> <span class="n">INFO</span> <span class="n">How</span> <span class="n">quickly</span> <span class="n">daft</span> <span class="n">jumping</span> <span class="n">zebras</span> <span class="n">vex</span><span class="o">.</span>
<span class="mi">69</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="n">WARNING</span> <span class="n">Jail</span> <span class="n">zesty</span> <span class="n">vixen</span> <span class="n">who</span> <span class="n">grabbed</span> <span class="n">pay</span> <span class="kn">from</span> <span class="nn">quack.</span>
<span class="mi">69</span> <span class="n">myapp</span><span class="o">.</span><span class="n">area2</span> <span class="n">ERROR</span> <span class="n">The</span> <span class="n">five</span> <span class="n">boxing</span> <span class="n">wizards</span> <span class="n">jump</span> <span class="n">quickly</span><span class="o">.</span>
</pre></div>
</div>
<p>Note that there are some security issues with pickle in some scenarios. If
these affect you, you can use an alternative serialization scheme by overriding
the <tt class="xref py py-meth docutils literal"><span class="pre">makePickle()</span></tt> method and implementing your alternative there, as
well as adapting the above script to use your alternative serialization.</p>
</div>
<div class="section" id="adding-contextual-information-to-your-logging-output">
<span id="context-info"></span><h2>Adding contextual information to your logging output<a class="headerlink" href="#adding-contextual-information-to-your-logging-output" title="Permalink to this headline">¶</a></h2>
<p>Sometimes you want logging output to contain contextual information in
addition to the parameters passed to the logging call. For example, in a
networked application, it may be desirable to log client-specific information
in the log (e.g. remote client’s username, or IP address). Although you could
use the <em>extra</em> parameter to achieve this, it’s not always convenient to pass
the information in this way. While it might be tempting to create
<tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt> instances on a per-connection basis, this is not a good idea
because these instances are not garbage collected. While this is not a problem
in practice, when the number of <tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt> instances is dependent on the
level of granularity you want to use in logging an application, it could
be hard to manage if the number of <tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt> instances becomes
effectively unbounded.</p>
<div class="section" id="using-loggeradapters-to-impart-contextual-information">
<h3>Using LoggerAdapters to impart contextual information<a class="headerlink" href="#using-loggeradapters-to-impart-contextual-information" title="Permalink to this headline">¶</a></h3>
<p>An easy way in which you can pass contextual information to be output along
with logging event information is to use the <tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt> class.
This class is designed to look like a <tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt>, so that you can call
<tt class="xref py py-meth docutils literal"><span class="pre">debug()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">info()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">warning()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">error()</span></tt>,
<tt class="xref py py-meth docutils literal"><span class="pre">exception()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">critical()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">log()</span></tt>. These methods have the
same signatures as their counterparts in <tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt>, so you can use the
two types of instances interchangeably.</p>
<p>When you create an instance of <tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt>, you pass it a
<tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt> instance and a dict-like object which contains your contextual
information. When you call one of the logging methods on an instance of
<tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt>, it delegates the call to the underlying instance of
<tt class="xref py py-class docutils literal"><span class="pre">Logger</span></tt> passed to its constructor, and arranges to pass the contextual
information in the delegated call. Here’s a snippet from the code of
<tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt>:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">def</span> <span class="nf">debug</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">msg</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> Delegate a debug call to the underlying logger, after adding</span>
<span class="sd"> contextual information from this adapter instance.</span>
<span class="sd"> """</span>
<span class="n">msg</span><span class="p">,</span> <span class="n">kwargs</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">process</span><span class="p">(</span><span class="n">msg</span><span class="p">,</span> <span class="n">kwargs</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">logger</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="n">msg</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span>
</pre></div>
</div>
<p>The <tt class="xref py py-meth docutils literal"><span class="pre">process()</span></tt> method of <tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt> is where the contextual
information is added to the logging output. It’s passed the message and
keyword arguments of the logging call, and it passes back (potentially)
modified versions of these to use in the call to the underlying logger. The
default implementation of this method leaves the message alone, but inserts
an ‘extra’ key in the keyword argument whose value is the dict-like object
passed to the constructor. Of course, if you had passed an ‘extra’ keyword
argument in the call to the adapter, it will be silently overwritten.</p>
<p>The advantage of using ‘extra’ is that the values in the dict-like object are
merged into the <tt class="xref py py-class docutils literal"><span class="pre">LogRecord</span></tt> instance’s __dict__, allowing you to use
customized strings with your <tt class="xref py py-class docutils literal"><span class="pre">Formatter</span></tt> instances which know about
the keys of the dict-like object. If you need a different method, e.g. if you
want to prepend or append the contextual information to the message string,
you just need to subclass <tt class="xref py py-class docutils literal"><span class="pre">LoggerAdapter</span></tt> and override <tt class="xref py py-meth docutils literal"><span class="pre">process()</span></tt>
to do what you need. Here’s an example script which uses this class, which
also illustrates what dict-like behaviour is needed from an arbitrary
‘dict-like’ object for use in the constructor:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="k">class</span> <span class="nc">ConnInfo</span><span class="p">:</span>
<span class="sd">"""</span>
<span class="sd"> An example class which shows how an arbitrary class can be used as</span>
<span class="sd"> the 'extra' context information repository passed to a LoggerAdapter.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="nf">__getitem__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> To allow this instance to look like a dict.</span>
<span class="sd"> """</span>
<span class="kn">from</span> <span class="nn">random</span> <span class="k">import</span> <span class="n">choice</span>
<span class="k">if</span> <span class="n">name</span> <span class="o">==</span> <span class="s">'ip'</span><span class="p">:</span>
<span class="n">result</span> <span class="o">=</span> <span class="n">choice</span><span class="p">([</span><span class="s">'127.0.0.1'</span><span class="p">,</span> <span class="s">'192.168.0.1'</span><span class="p">])</span>
<span class="k">elif</span> <span class="n">name</span> <span class="o">==</span> <span class="s">'user'</span><span class="p">:</span>
<span class="n">result</span> <span class="o">=</span> <span class="n">choice</span><span class="p">([</span><span class="s">'jim'</span><span class="p">,</span> <span class="s">'fred'</span><span class="p">,</span> <span class="s">'sheila'</span><span class="p">])</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">result</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">__dict__</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="s">'?'</span><span class="p">)</span>
<span class="k">return</span> <span class="n">result</span>
<span class="k">def</span> <span class="nf">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> To allow iteration over keys, which will be merged into</span>
<span class="sd"> the LogRecord dict before formatting and output.</span>
<span class="sd"> """</span>
<span class="n">keys</span> <span class="o">=</span> <span class="p">[</span><span class="s">'ip'</span><span class="p">,</span> <span class="s">'user'</span><span class="p">]</span>
<span class="n">keys</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">__dict__</span><span class="o">.</span><span class="n">keys</span><span class="p">())</span>
<span class="k">return</span> <span class="n">keys</span><span class="o">.</span><span class="n">__iter__</span><span class="p">()</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="kn">from</span> <span class="nn">random</span> <span class="k">import</span> <span class="n">choice</span>
<span class="n">levels</span> <span class="o">=</span> <span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">INFO</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">WARNING</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">ERROR</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">CRITICAL</span><span class="p">)</span>
<span class="n">a1</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">LoggerAdapter</span><span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s">'a.b.c'</span><span class="p">),</span>
<span class="p">{</span> <span class="s">'ip'</span> <span class="p">:</span> <span class="s">'123.231.231.123'</span><span class="p">,</span> <span class="s">'user'</span> <span class="p">:</span> <span class="s">'sheila'</span> <span class="p">})</span>
<span class="n">logging</span><span class="o">.</span><span class="n">basicConfig</span><span class="p">(</span><span class="n">level</span><span class="o">=</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span>
<span class="nb">format</span><span class="o">=</span><span class="s">'%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s'</span><span class="p">)</span>
<span class="n">a1</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'A debug message'</span><span class="p">)</span>
<span class="n">a1</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'An info message with %s'</span><span class="p">,</span> <span class="s">'some parameters'</span><span class="p">)</span>
<span class="n">a2</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">LoggerAdapter</span><span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="s">'d.e.f'</span><span class="p">),</span> <span class="n">ConnInfo</span><span class="p">())</span>
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">lvl</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">levels</span><span class="p">)</span>
<span class="n">lvlname</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">getLevelName</span><span class="p">(</span><span class="n">lvl</span><span class="p">)</span>
<span class="n">a2</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">lvl</span><span class="p">,</span> <span class="s">'A message at %s level with %d %s'</span><span class="p">,</span> <span class="n">lvlname</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="s">'parameters'</span><span class="p">)</span>
</pre></div>
</div>
<p>When this script is run, the output should look something like this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">023</span> <span class="n">a</span><span class="o">.</span><span class="n">b</span><span class="o">.</span><span class="n">c</span> <span class="n">DEBUG</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">debug</span> <span class="n">message</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">023</span> <span class="n">a</span><span class="o">.</span><span class="n">b</span><span class="o">.</span><span class="n">c</span> <span class="n">INFO</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">An</span> <span class="n">info</span> <span class="n">message</span> <span class="k">with</span> <span class="n">some</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">023</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">CRITICAL</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">CRITICAL</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">INFO</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">INFO</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">WARNING</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">WARNING</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">ERROR</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">ERROR</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">ERROR</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">ERROR</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">WARNING</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">WARNING</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">WARNING</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">WARNING</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">INFO</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">INFO</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">WARNING</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">WARNING</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2008</span><span class="o">-</span><span class="mi">01</span><span class="o">-</span><span class="mi">18</span> <span class="mi">14</span><span class="p">:</span><span class="mi">49</span><span class="p">:</span><span class="mi">54</span><span class="p">,</span><span class="mi">033</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">WARNING</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">WARNING</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
</pre></div>
</div>
</div>
<div class="section" id="using-filters-to-impart-contextual-information">
<span id="filters-contextual"></span><h3>Using Filters to impart contextual information<a class="headerlink" href="#using-filters-to-impart-contextual-information" title="Permalink to this headline">¶</a></h3>
<p>You can also add contextual information to log output using a user-defined
<tt class="xref py py-class docutils literal"><span class="pre">Filter</span></tt>. <tt class="docutils literal"><span class="pre">Filter</span></tt> instances are allowed to modify the <tt class="docutils literal"><span class="pre">LogRecords</span></tt>
passed to them, including adding additional attributes which can then be output
using a suitable format string, or if needed a custom <tt class="xref py py-class docutils literal"><span class="pre">Formatter</span></tt>.</p>
<p>For example in a web application, the request being processed (or at least,
the interesting parts of it) can be stored in a threadlocal
(<a class="reference internal" href="../library/threading.html#threading.local" title="threading.local"><tt class="xref py py-class docutils literal"><span class="pre">threading.local</span></tt></a>) variable, and then accessed from a <tt class="docutils literal"><span class="pre">Filter</span></tt> to
add, say, information from the request - say, the remote IP address and remote
user’s username - to the <tt class="docutils literal"><span class="pre">LogRecord</span></tt>, using the attribute names ‘ip’ and
‘user’ as in the <tt class="docutils literal"><span class="pre">LoggerAdapter</span></tt> example above. In that case, the same format
string can be used to get similar output to that shown above. Here’s an example
script:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">from</span> <span class="nn">random</span> <span class="k">import</span> <span class="n">choice</span>
<span class="k">class</span> <span class="nc">ContextFilter</span><span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">Filter</span><span class="p">):</span>
<span class="sd">"""</span>
<span class="sd"> This is a filter which injects contextual information into the log.</span>
<span class="sd"> Rather than use actual contextual information, we just use random</span>
<span class="sd"> data in this demo.</span>
<span class="sd"> """</span>
<span class="n">USERS</span> <span class="o">=</span> <span class="p">[</span><span class="s">'jim'</span><span class="p">,</span> <span class="s">'fred'</span><span class="p">,</span> <span class="s">'sheila'</span><span class="p">]</span>
<span class="n">IPS</span> <span class="o">=</span> <span class="p">[</span><span class="s">'123.231.231.123'</span><span class="p">,</span> <span class="s">'127.0.0.1'</span><span class="p">,</span> <span class="s">'192.168.0.1'</span><span class="p">]</span>
<span class="k">def</span> <span class="nf">filter</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">record</span><span class="p">):</span>
<span class="n">record</span><span class="o">.</span><span class="n">ip</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">ContextFilter</span><span class="o">.</span><span class="n">IPS</span><span class="p">)</span>
<span class="n">record</span><span class="o">.</span><span class="n">user</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">ContextFilter</span><span class="o">.</span><span class="n">USERS</span><span class="p">)</span>
<span class="k">return</span> <span class="k">True</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">levels</span> <span class="o">=</span> <span class="p">(</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">INFO</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">WARNING</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">ERROR</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">CRITICAL</span><span class="p">)</span>
<span class="n">logging</span><span class="o">.</span><span class="n">basicConfig</span><span class="p">(</span><span class="n">level</span><span class="o">=</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span>
<span class="nb">format</span><span class="o">=</span><span class="s">'%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s'</span><span class="p">)</span>
<span class="n">a1</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="s">'a.b.c'</span><span class="p">)</span>
<span class="n">a2</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="s">'d.e.f'</span><span class="p">)</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">ContextFilter</span><span class="p">()</span>
<span class="n">a1</span><span class="o">.</span><span class="n">addFilter</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="n">a2</span><span class="o">.</span><span class="n">addFilter</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="n">a1</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'A debug message'</span><span class="p">)</span>
<span class="n">a1</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'An info message with %s'</span><span class="p">,</span> <span class="s">'some parameters'</span><span class="p">)</span>
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">lvl</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">levels</span><span class="p">)</span>
<span class="n">lvlname</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">getLevelName</span><span class="p">(</span><span class="n">lvl</span><span class="p">)</span>
<span class="n">a2</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">lvl</span><span class="p">,</span> <span class="s">'A message at %s level with %d %s'</span><span class="p">,</span> <span class="n">lvlname</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="s">'parameters'</span><span class="p">)</span>
</pre></div>
</div>
<p>which, when run, produces something like:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">292</span> <span class="n">a</span><span class="o">.</span><span class="n">b</span><span class="o">.</span><span class="n">c</span> <span class="n">DEBUG</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">debug</span> <span class="n">message</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">a</span><span class="o">.</span><span class="n">b</span><span class="o">.</span><span class="n">c</span> <span class="n">INFO</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">An</span> <span class="n">info</span> <span class="n">message</span> <span class="k">with</span> <span class="n">some</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">CRITICAL</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">CRITICAL</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">ERROR</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">ERROR</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">DEBUG</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">DEBUG</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">ERROR</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">ERROR</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">CRITICAL</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">CRITICAL</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">CRITICAL</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">CRITICAL</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">300</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">DEBUG</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">192.168</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">jim</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">DEBUG</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">301</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">ERROR</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">127.0</span><span class="o">.</span><span class="mf">0.1</span> <span class="n">User</span><span class="p">:</span> <span class="n">sheila</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">ERROR</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">301</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">DEBUG</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">DEBUG</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
<span class="mi">2010</span><span class="o">-</span><span class="mi">09</span><span class="o">-</span><span class="mi">06</span> <span class="mi">22</span><span class="p">:</span><span class="mi">38</span><span class="p">:</span><span class="mi">15</span><span class="p">,</span><span class="mi">301</span> <span class="n">d</span><span class="o">.</span><span class="n">e</span><span class="o">.</span><span class="n">f</span> <span class="n">INFO</span> <span class="n">IP</span><span class="p">:</span> <span class="mf">123.231</span><span class="o">.</span><span class="mf">231.123</span> <span class="n">User</span><span class="p">:</span> <span class="n">fred</span> <span class="n">A</span> <span class="n">message</span> <span class="n">at</span> <span class="n">INFO</span> <span class="n">level</span> <span class="k">with</span> <span class="mi">2</span> <span class="n">parameters</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="logging-to-a-single-file-from-multiple-processes">
<span id="multiple-processes"></span><h2>Logging to a single file from multiple processes<a class="headerlink" href="#logging-to-a-single-file-from-multiple-processes" title="Permalink to this headline">¶</a></h2>
<p>Although logging is thread-safe, and logging to a single file from multiple
threads in a single process <em>is</em> supported, logging to a single file from
<em>multiple processes</em> is <em>not</em> supported, because there is no standard way to
serialize access to a single file across multiple processes in Python. If you
need to log to a single file from multiple processes, one way of doing this is
to have all the processes log to a <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.SocketHandler" title="logging.handlers.SocketHandler"><tt class="xref py py-class docutils literal"><span class="pre">SocketHandler</span></tt></a>, and have a separate
process which implements a socket server which reads from the socket and logs
to file. (If you prefer, you can dedicate one thread in one of the existing
processes to perform this function.) The following section documents this
approach in more detail and includes a working socket receiver which can be
used as a starting point for you to adapt in your own applications.</p>
<p>If you are using a recent version of Python which includes the
<a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><tt class="xref py py-mod docutils literal"><span class="pre">multiprocessing</span></tt></a> module, you could write your own handler which uses the
<tt class="xref py py-class docutils literal"><span class="pre">Lock</span></tt> class from this module to serialize access to the file from
your processes. The existing <tt class="xref py py-class docutils literal"><span class="pre">FileHandler</span></tt> and subclasses do not make
use of <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><tt class="xref py py-mod docutils literal"><span class="pre">multiprocessing</span></tt></a> at present, though they may do so in the future.
Note that at present, the <a class="reference internal" href="../library/multiprocessing.html#module-multiprocessing" title="multiprocessing: Process-based parallelism."><tt class="xref py py-mod docutils literal"><span class="pre">multiprocessing</span></tt></a> module does not provide
working lock functionality on all platforms (see
<a class="reference external" href="http://bugs.python.org/issue3770">http://bugs.python.org/issue3770</a>).</p>
<p>Alternatively, you can use a <tt class="docutils literal"><span class="pre">Queue</span></tt> and a <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueHandler" title="logging.handlers.QueueHandler"><tt class="xref py py-class docutils literal"><span class="pre">QueueHandler</span></tt></a> to send
all logging events to one of the processes in your multi-process application.
The following example script demonstrates how you can do this; in the example
a separate listener process listens for events sent by other processes and logs
them according to its own logging configuration. Although the example only
demonstrates one way of doing it (for example, you may want to use a listener
thread rather than a separate listener process – the implementation would be
analogous) it does allow for completely different logging configurations for
the listener and the other processes in your application, and can be used as
the basis for code meeting your own specific requirements:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="c"># You'll need these imports in your own code</span>
<span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">logging.handlers</span>
<span class="kn">import</span> <span class="nn">multiprocessing</span>
<span class="c"># Next two import lines for this demo only</span>
<span class="kn">from</span> <span class="nn">random</span> <span class="k">import</span> <span class="n">choice</span><span class="p">,</span> <span class="n">random</span>
<span class="kn">import</span> <span class="nn">time</span>
<span class="c">#</span>
<span class="c"># Because you'll want to define the logging configurations for listener and workers, the</span>
<span class="c"># listener and worker process functions take a configurer parameter which is a callable</span>
<span class="c"># for configuring logging for that process. These functions are also passed the queue,</span>
<span class="c"># which they use for communication.</span>
<span class="c">#</span>
<span class="c"># In practice, you can configure the listener however you want, but note that in this</span>
<span class="c"># simple example, the listener does not apply level or filter logic to received records.</span>
<span class="c"># In practice, you would probably want to do this logic in the worker processes, to avoid</span>
<span class="c"># sending events which would be filtered out between processes.</span>
<span class="c">#</span>
<span class="c"># The size of the rotated files is made small so you can see the results easily.</span>
<span class="k">def</span> <span class="nf">listener_configurer</span><span class="p">():</span>
<span class="n">root</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="n">h</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">RotatingFileHandler</span><span class="p">(</span><span class="s">'mptest.log'</span><span class="p">,</span> <span class="s">'a'</span><span class="p">,</span> <span class="mi">300</span><span class="p">,</span> <span class="mi">10</span><span class="p">)</span>
<span class="n">f</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">Formatter</span><span class="p">(</span><span class="s">'%(asctime)s %(processName)-10s %(name)s %(levelname)-8s %(message)s'</span><span class="p">)</span>
<span class="n">h</span><span class="o">.</span><span class="n">setFormatter</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="n">root</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">h</span><span class="p">)</span>
<span class="c"># This is the listener process top-level loop: wait for logging events</span>
<span class="c"># (LogRecords)on the queue and handle them, quit when you get a None for a</span>
<span class="c"># LogRecord.</span>
<span class="k">def</span> <span class="nf">listener_process</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">configurer</span><span class="p">):</span>
<span class="n">configurer</span><span class="p">()</span>
<span class="k">while</span> <span class="k">True</span><span class="p">:</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">record</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>
<span class="k">if</span> <span class="n">record</span> <span class="ow">is</span> <span class="k">None</span><span class="p">:</span> <span class="c"># We send this as a sentinel to tell the listener to quit.</span>
<span class="k">break</span>
<span class="n">logger</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="n">record</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">handle</span><span class="p">(</span><span class="n">record</span><span class="p">)</span> <span class="c"># No level or filter logic applied - just do it!</span>
<span class="k">except</span> <span class="p">(</span><span class="ne">KeyboardInterrupt</span><span class="p">,</span> <span class="ne">SystemExit</span><span class="p">):</span>
<span class="k">raise</span>
<span class="k">except</span><span class="p">:</span>
<span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">traceback</span>
<span class="nb">print</span> <span class="o">>></span> <span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">,</span> <span class="s">'Whoops! Problem:'</span>
<span class="n">traceback</span><span class="o">.</span><span class="n">print_exc</span><span class="p">(</span><span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
<span class="c"># Arrays used for random selections in this demo</span>
<span class="n">LEVELS</span> <span class="o">=</span> <span class="p">[</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">INFO</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">WARNING</span><span class="p">,</span>
<span class="n">logging</span><span class="o">.</span><span class="n">ERROR</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">CRITICAL</span><span class="p">]</span>
<span class="n">LOGGERS</span> <span class="o">=</span> <span class="p">[</span><span class="s">'a.b.c'</span><span class="p">,</span> <span class="s">'d.e.f'</span><span class="p">]</span>
<span class="n">MESSAGES</span> <span class="o">=</span> <span class="p">[</span>
<span class="s">'Random message #1'</span><span class="p">,</span>
<span class="s">'Random message #2'</span><span class="p">,</span>
<span class="s">'Random message #3'</span><span class="p">,</span>
<span class="p">]</span>
<span class="c"># The worker configuration is done at the start of the worker process run.</span>
<span class="c"># Note that on Windows you can't rely on fork semantics, so each process</span>
<span class="c"># will run the logging configuration code when it starts.</span>
<span class="k">def</span> <span class="nf">worker_configurer</span><span class="p">(</span><span class="n">queue</span><span class="p">):</span>
<span class="n">h</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">QueueHandler</span><span class="p">(</span><span class="n">queue</span><span class="p">)</span> <span class="c"># Just the one handler needed</span>
<span class="n">root</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="n">root</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">h</span><span class="p">)</span>
<span class="n">root</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">DEBUG</span><span class="p">)</span> <span class="c"># send all messages, for demo; no other level or filter logic applied.</span>
<span class="c"># This is the worker process top-level loop, which just logs ten events with</span>
<span class="c"># random intervening delays before terminating.</span>
<span class="c"># The print messages are just so you know it's doing something!</span>
<span class="k">def</span> <span class="nf">worker_process</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">configurer</span><span class="p">):</span>
<span class="n">configurer</span><span class="p">(</span><span class="n">queue</span><span class="p">)</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">current_process</span><span class="p">()</span><span class="o">.</span><span class="n">name</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'Worker started: %s'</span> <span class="o">%</span> <span class="n">name</span><span class="p">)</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="n">random</span><span class="p">())</span>
<span class="n">logger</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="n">choice</span><span class="p">(</span><span class="n">LOGGERS</span><span class="p">))</span>
<span class="n">level</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">LEVELS</span><span class="p">)</span>
<span class="n">message</span> <span class="o">=</span> <span class="n">choice</span><span class="p">(</span><span class="n">MESSAGES</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">level</span><span class="p">,</span> <span class="n">message</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s">'Worker finished: %s'</span> <span class="o">%</span> <span class="n">name</span><span class="p">)</span>
<span class="c"># Here's where the demo gets orchestrated. Create the queue, create and start</span>
<span class="c"># the listener, create ten workers and start them, wait for them to finish,</span>
<span class="c"># then send a None to the queue to tell the listener to finish.</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="n">queue</span> <span class="o">=</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">Queue</span><span class="p">(</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="n">listener</span> <span class="o">=</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">Process</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">listener_process</span><span class="p">,</span>
<span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">listener_configurer</span><span class="p">))</span>
<span class="n">listener</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">workers</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="n">worker</span> <span class="o">=</span> <span class="n">multiprocessing</span><span class="o">.</span><span class="n">Process</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">worker_process</span><span class="p">,</span>
<span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="n">queue</span><span class="p">,</span> <span class="n">worker_configurer</span><span class="p">))</span>
<span class="n">workers</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">worker</span><span class="p">)</span>
<span class="n">worker</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="k">for</span> <span class="n">w</span> <span class="ow">in</span> <span class="n">workers</span><span class="p">:</span>
<span class="n">w</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
<span class="n">queue</span><span class="o">.</span><span class="n">put_nowait</span><span class="p">(</span><span class="k">None</span><span class="p">)</span>
<span class="n">listener</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">main</span><span class="p">()</span>
</pre></div>
</div>
<p>A variant of the above script keeps the logging in the main process, in a
separate thread:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">logging.config</span>
<span class="kn">import</span> <span class="nn">logging.handlers</span>
<span class="kn">from</span> <span class="nn">multiprocessing</span> <span class="k">import</span> <span class="n">Process</span><span class="p">,</span> <span class="n">Queue</span>
<span class="kn">import</span> <span class="nn">random</span>
<span class="kn">import</span> <span class="nn">threading</span>
<span class="kn">import</span> <span class="nn">time</span>
<span class="k">def</span> <span class="nf">logger_thread</span><span class="p">(</span><span class="n">q</span><span class="p">):</span>
<span class="k">while</span> <span class="k">True</span><span class="p">:</span>
<span class="n">record</span> <span class="o">=</span> <span class="n">q</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>
<span class="k">if</span> <span class="n">record</span> <span class="ow">is</span> <span class="k">None</span><span class="p">:</span>
<span class="k">break</span>
<span class="n">logger</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="n">record</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
<span class="n">logger</span><span class="o">.</span><span class="n">handle</span><span class="p">(</span><span class="n">record</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">worker_process</span><span class="p">(</span><span class="n">q</span><span class="p">):</span>
<span class="n">qh</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">QueueHandler</span><span class="p">(</span><span class="n">q</span><span class="p">)</span>
<span class="n">root</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="n">root</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">DEBUG</span><span class="p">)</span>
<span class="n">root</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">qh</span><span class="p">)</span>
<span class="n">levels</span> <span class="o">=</span> <span class="p">[</span><span class="n">logging</span><span class="o">.</span><span class="n">DEBUG</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">INFO</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">WARNING</span><span class="p">,</span> <span class="n">logging</span><span class="o">.</span><span class="n">ERROR</span><span class="p">,</span>
<span class="n">logging</span><span class="o">.</span><span class="n">CRITICAL</span><span class="p">]</span>
<span class="n">loggers</span> <span class="o">=</span> <span class="p">[</span><span class="s">'foo'</span><span class="p">,</span> <span class="s">'foo.bar'</span><span class="p">,</span> <span class="s">'foo.bar.baz'</span><span class="p">,</span>
<span class="s">'spam'</span><span class="p">,</span> <span class="s">'spam.ham'</span><span class="p">,</span> <span class="s">'spam.ham.eggs'</span><span class="p">]</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">100</span><span class="p">):</span>
<span class="n">lvl</span> <span class="o">=</span> <span class="n">random</span><span class="o">.</span><span class="n">choice</span><span class="p">(</span><span class="n">levels</span><span class="p">)</span>
<span class="n">logger</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="n">random</span><span class="o">.</span><span class="n">choice</span><span class="p">(</span><span class="n">loggers</span><span class="p">))</span>
<span class="n">logger</span><span class="o">.</span><span class="n">log</span><span class="p">(</span><span class="n">lvl</span><span class="p">,</span> <span class="s">'Message no. %d'</span><span class="p">,</span> <span class="n">i</span><span class="p">)</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">q</span> <span class="o">=</span> <span class="n">Queue</span><span class="p">()</span>
<span class="n">d</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'version'</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span>
<span class="s">'formatters'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'detailed'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'class'</span><span class="p">:</span> <span class="s">'logging.Formatter'</span><span class="p">,</span>
<span class="s">'format'</span><span class="p">:</span> <span class="s">'%(asctime)s %(name)-15s %(levelname)-8s %(processName)-10s %(message)s'</span>
<span class="p">}</span>
<span class="p">},</span>
<span class="s">'handlers'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'console'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'class'</span><span class="p">:</span> <span class="s">'logging.StreamHandler'</span><span class="p">,</span>
<span class="s">'level'</span><span class="p">:</span> <span class="s">'INFO'</span><span class="p">,</span>
<span class="p">},</span>
<span class="s">'file'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'class'</span><span class="p">:</span> <span class="s">'logging.FileHandler'</span><span class="p">,</span>
<span class="s">'filename'</span><span class="p">:</span> <span class="s">'mplog.log'</span><span class="p">,</span>
<span class="s">'mode'</span><span class="p">:</span> <span class="s">'w'</span><span class="p">,</span>
<span class="s">'formatter'</span><span class="p">:</span> <span class="s">'detailed'</span><span class="p">,</span>
<span class="p">},</span>
<span class="s">'foofile'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'class'</span><span class="p">:</span> <span class="s">'logging.FileHandler'</span><span class="p">,</span>
<span class="s">'filename'</span><span class="p">:</span> <span class="s">'mplog-foo.log'</span><span class="p">,</span>
<span class="s">'mode'</span><span class="p">:</span> <span class="s">'w'</span><span class="p">,</span>
<span class="s">'formatter'</span><span class="p">:</span> <span class="s">'detailed'</span><span class="p">,</span>
<span class="p">},</span>
<span class="s">'errors'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'class'</span><span class="p">:</span> <span class="s">'logging.FileHandler'</span><span class="p">,</span>
<span class="s">'filename'</span><span class="p">:</span> <span class="s">'mplog-errors.log'</span><span class="p">,</span>
<span class="s">'mode'</span><span class="p">:</span> <span class="s">'w'</span><span class="p">,</span>
<span class="s">'level'</span><span class="p">:</span> <span class="s">'ERROR'</span><span class="p">,</span>
<span class="s">'formatter'</span><span class="p">:</span> <span class="s">'detailed'</span><span class="p">,</span>
<span class="p">},</span>
<span class="p">},</span>
<span class="s">'loggers'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'foo'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'handlers'</span> <span class="p">:</span> <span class="p">[</span><span class="s">'foofile'</span><span class="p">]</span>
<span class="p">}</span>
<span class="p">},</span>
<span class="s">'root'</span><span class="p">:</span> <span class="p">{</span>
<span class="s">'level'</span><span class="p">:</span> <span class="s">'DEBUG'</span><span class="p">,</span>
<span class="s">'handlers'</span><span class="p">:</span> <span class="p">[</span><span class="s">'console'</span><span class="p">,</span> <span class="s">'file'</span><span class="p">,</span> <span class="s">'errors'</span><span class="p">]</span>
<span class="p">},</span>
<span class="p">}</span>
<span class="n">workers</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">):</span>
<span class="n">wp</span> <span class="o">=</span> <span class="n">Process</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">worker_process</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="s">'worker %d'</span> <span class="o">%</span> <span class="p">(</span><span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">),</span> <span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="n">q</span><span class="p">,))</span>
<span class="n">workers</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">wp</span><span class="p">)</span>
<span class="n">wp</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="n">logging</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">dictConfig</span><span class="p">(</span><span class="n">d</span><span class="p">)</span>
<span class="n">lp</span> <span class="o">=</span> <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">logger_thread</span><span class="p">,</span> <span class="n">args</span><span class="o">=</span><span class="p">(</span><span class="n">q</span><span class="p">,))</span>
<span class="n">lp</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
<span class="c"># At this point, the main process could do some useful work of its own</span>
<span class="c"># Once it's done that, it can wait for the workers to terminate...</span>
<span class="k">for</span> <span class="n">wp</span> <span class="ow">in</span> <span class="n">workers</span><span class="p">:</span>
<span class="n">wp</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
<span class="c"># And now tell the logging thread to finish up, too</span>
<span class="n">q</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="k">None</span><span class="p">)</span>
<span class="n">lp</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
</pre></div>
</div>
<p>This variant shows how you can e.g. apply configuration for particular loggers
- e.g. the <tt class="docutils literal"><span class="pre">foo</span></tt> logger has a special handler which stores all events in the
<tt class="docutils literal"><span class="pre">foo</span></tt> subsystem in a file <tt class="docutils literal"><span class="pre">mplog-foo.log</span></tt>. This will be used by the logging
machinery in the main process (even though the logging events are generated in
the worker processes) to direct the messages to the appropriate destinations.</p>
</div>
<div class="section" id="using-file-rotation">
<h2>Using file rotation<a class="headerlink" href="#using-file-rotation" title="Permalink to this headline">¶</a></h2>
<p>Sometimes you want to let a log file grow to a certain size, then open a new
file and log to that. You may want to keep a certain number of these files, and
when that many files have been created, rotate the files so that the number of
files and the size of the files both remain bounded. For this usage pattern, the
logging package provides a <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.RotatingFileHandler" title="logging.handlers.RotatingFileHandler"><tt class="xref py py-class docutils literal"><span class="pre">RotatingFileHandler</span></tt></a>:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">glob</span>
<span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">logging.handlers</span>
<span class="n">LOG_FILENAME</span> <span class="o">=</span> <span class="s">'logging_rotatingfile_example.out'</span>
<span class="c"># Set up a specific logger with our desired output level</span>
<span class="n">my_logger</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="s">'MyLogger'</span><span class="p">)</span>
<span class="n">my_logger</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">DEBUG</span><span class="p">)</span>
<span class="c"># Add the log message handler to the logger</span>
<span class="n">handler</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">RotatingFileHandler</span><span class="p">(</span>
<span class="n">LOG_FILENAME</span><span class="p">,</span> <span class="n">maxBytes</span><span class="o">=</span><span class="mi">20</span><span class="p">,</span> <span class="n">backupCount</span><span class="o">=</span><span class="mi">5</span><span class="p">)</span>
<span class="n">my_logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">handler</span><span class="p">)</span>
<span class="c"># Log some messages</span>
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">20</span><span class="p">):</span>
<span class="n">my_logger</span><span class="o">.</span><span class="n">debug</span><span class="p">(</span><span class="s">'i = %d'</span> <span class="o">%</span> <span class="n">i</span><span class="p">)</span>
<span class="c"># See what files are created</span>
<span class="n">logfiles</span> <span class="o">=</span> <span class="n">glob</span><span class="o">.</span><span class="n">glob</span><span class="p">(</span><span class="s">'%s*'</span> <span class="o">%</span> <span class="n">LOG_FILENAME</span><span class="p">)</span>
<span class="k">for</span> <span class="n">filename</span> <span class="ow">in</span> <span class="n">logfiles</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span>
</pre></div>
</div>
<p>The result should be 6 separate files, each with part of the log history for the
application:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span>
<span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="mi">1</span>
<span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="mi">2</span>
<span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="mi">3</span>
<span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="mi">4</span>
<span class="n">logging_rotatingfile_example</span><span class="o">.</span><span class="n">out</span><span class="o">.</span><span class="mi">5</span>
</pre></div>
</div>
<p>The most current file is always <tt class="file docutils literal"><span class="pre">logging_rotatingfile_example.out</span></tt>,
and each time it reaches the size limit it is renamed with the suffix
<tt class="docutils literal"><span class="pre">.1</span></tt>. Each of the existing backup files is renamed to increment the suffix
(<tt class="docutils literal"><span class="pre">.1</span></tt> becomes <tt class="docutils literal"><span class="pre">.2</span></tt>, etc.) and the <tt class="docutils literal"><span class="pre">.6</span></tt> file is erased.</p>
<p>Obviously this example sets the log length much much too small as an extreme
example. You would want to set <em>maxBytes</em> to an appropriate value.</p>
</div>
<div class="section" id="subclassing-queuehandler-a-zeromq-example">
<span id="zeromq-handlers"></span><h2>Subclassing QueueHandler - a ZeroMQ example<a class="headerlink" href="#subclassing-queuehandler-a-zeromq-example" title="Permalink to this headline">¶</a></h2>
<p>You can use a <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueHandler" title="logging.handlers.QueueHandler"><tt class="xref py py-class docutils literal"><span class="pre">QueueHandler</span></tt></a> subclass to send messages to other kinds
of queues, for example a ZeroMQ ‘publish’ socket. In the example below,the
socket is created separately and passed to the handler (as its ‘queue’):</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">zmq</span> <span class="c"># using pyzmq, the Python binding for ZeroMQ</span>
<span class="kn">import</span> <span class="nn">json</span> <span class="c"># for serializing records portably</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Context</span><span class="p">()</span>
<span class="n">sock</span> <span class="o">=</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Socket</span><span class="p">(</span><span class="n">ctx</span><span class="p">,</span> <span class="n">zmq</span><span class="o">.</span><span class="n">PUB</span><span class="p">)</span> <span class="c"># or zmq.PUSH, or other suitable value</span>
<span class="n">sock</span><span class="o">.</span><span class="n">bind</span><span class="p">(</span><span class="s">'tcp://*:5556'</span><span class="p">)</span> <span class="c"># or wherever</span>
<span class="k">class</span> <span class="nc">ZeroMQSocketHandler</span><span class="p">(</span><span class="n">QueueHandler</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">enqueue</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">record</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">record</span><span class="o">.</span><span class="n">__dict__</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="n">handler</span> <span class="o">=</span> <span class="n">ZeroMQSocketHandler</span><span class="p">(</span><span class="n">sock</span><span class="p">)</span>
</pre></div>
</div>
<p>Of course there are other ways of organizing this, for example passing in the
data needed by the handler to create the socket:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ZeroMQSocketHandler</span><span class="p">(</span><span class="n">QueueHandler</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">uri</span><span class="p">,</span> <span class="n">socktype</span><span class="o">=</span><span class="n">zmq</span><span class="o">.</span><span class="n">PUB</span><span class="p">,</span> <span class="n">ctx</span><span class="o">=</span><span class="k">None</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">ctx</span> <span class="o">=</span> <span class="n">ctx</span> <span class="ow">or</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Context</span><span class="p">()</span>
<span class="n">socket</span> <span class="o">=</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Socket</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">ctx</span><span class="p">,</span> <span class="n">socktype</span><span class="p">)</span>
<span class="n">socket</span><span class="o">.</span><span class="n">bind</span><span class="p">(</span><span class="n">uri</span><span class="p">)</span>
<span class="n">QueueHandler</span><span class="o">.</span><span class="n">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">socket</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">enqueue</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">record</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">json</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">record</span><span class="o">.</span><span class="n">__dict__</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">close</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
</div>
<div class="section" id="subclassing-queuelistener-a-zeromq-example">
<h2>Subclassing QueueListener - a ZeroMQ example<a class="headerlink" href="#subclassing-queuelistener-a-zeromq-example" title="Permalink to this headline">¶</a></h2>
<p>You can also subclass <a class="reference internal" href="../library/logging.handlers.html#logging.handlers.QueueListener" title="logging.handlers.QueueListener"><tt class="xref py py-class docutils literal"><span class="pre">QueueListener</span></tt></a> to get messages from other kinds
of queues, for example a ZeroMQ ‘subscribe’ socket. Here’s an example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">class</span> <span class="nc">ZeroMQSocketListener</span><span class="p">(</span><span class="n">QueueListener</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">uri</span><span class="p">,</span> <span class="o">*</span><span class="n">handlers</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">ctx</span> <span class="o">=</span> <span class="n">kwargs</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'ctx'</span><span class="p">)</span> <span class="ow">or</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Context</span><span class="p">()</span>
<span class="n">socket</span> <span class="o">=</span> <span class="n">zmq</span><span class="o">.</span><span class="n">Socket</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">ctx</span><span class="p">,</span> <span class="n">zmq</span><span class="o">.</span><span class="n">SUB</span><span class="p">)</span>
<span class="n">socket</span><span class="o">.</span><span class="n">setsockopt</span><span class="p">(</span><span class="n">zmq</span><span class="o">.</span><span class="n">SUBSCRIBE</span><span class="p">,</span> <span class="s">''</span><span class="p">)</span> <span class="c"># subscribe to everything</span>
<span class="n">socket</span><span class="o">.</span><span class="n">connect</span><span class="p">(</span><span class="n">uri</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">dequeue</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">msg</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">queue</span><span class="o">.</span><span class="n">recv</span><span class="p">()</span>
<span class="k">return</span> <span class="n">logging</span><span class="o">.</span><span class="n">makeLogRecord</span><span class="p">(</span><span class="n">json</span><span class="o">.</span><span class="n">loads</span><span class="p">(</span><span class="n">msg</span><span class="p">))</span>
</pre></div>
</div>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="docutils">
<dt>Module <a class="reference internal" href="../library/logging.html#module-logging" title="logging: Flexible event logging system for applications."><tt class="xref py py-mod docutils literal"><span class="pre">logging</span></tt></a></dt>
<dd>API reference for the logging module.</dd>
<dt>Module <a class="reference internal" href="../library/logging.config.html#module-logging.config" title="logging.config: Configuration of the logging module."><tt class="xref py py-mod docutils literal"><span class="pre">logging.config</span></tt></a></dt>
<dd>Configuration API for the logging module.</dd>
<dt>Module <a class="reference internal" href="../library/logging.handlers.html#module-logging.handlers" title="logging.handlers: Handlers for the logging module."><tt class="xref py py-mod docutils literal"><span class="pre">logging.handlers</span></tt></a></dt>
<dd>Useful handlers included with the logging module.</dd>
</dl>
<p><a class="reference internal" href="logging.html#logging-basic-tutorial"><em>A basic logging tutorial</em></a></p>
<p class="last"><a class="reference internal" href="logging.html#logging-advanced-tutorial"><em>A more advanced logging tutorial</em></a></p>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Logging Cookbook</a><ul>
<li><a class="reference internal" href="#using-logging-in-multiple-modules">Using logging in multiple modules</a></li>
<li><a class="reference internal" href="#multiple-handlers-and-formatters">Multiple handlers and formatters</a></li>
<li><a class="reference internal" href="#logging-to-multiple-destinations">Logging to multiple destinations</a></li>
<li><a class="reference internal" href="#configuration-server-example">Configuration server example</a></li>
<li><a class="reference internal" href="#dealing-with-handlers-that-block">Dealing with handlers that block</a></li>
<li><a class="reference internal" href="#sending-and-receiving-logging-events-across-a-network">Sending and receiving logging events across a network</a></li>
<li><a class="reference internal" href="#adding-contextual-information-to-your-logging-output">Adding contextual information to your logging output</a><ul>
<li><a class="reference internal" href="#using-loggeradapters-to-impart-contextual-information">Using LoggerAdapters to impart contextual information</a></li>
<li><a class="reference internal" href="#using-filters-to-impart-contextual-information">Using Filters to impart contextual information</a></li>
</ul>
</li>
<li><a class="reference internal" href="#logging-to-a-single-file-from-multiple-processes">Logging to a single file from multiple processes</a></li>
<li><a class="reference internal" href="#using-file-rotation">Using file rotation</a></li>
<li><a class="reference internal" href="#subclassing-queuehandler-a-zeromq-example">Subclassing QueueHandler - a ZeroMQ example</a></li>
<li><a class="reference internal" href="#subclassing-queuelistener-a-zeromq-example">Subclassing QueueListener - a ZeroMQ example</a></li>
</ul>
</li>
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distrib
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Mandriva
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x86_64
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contrib-backports
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3ba3bd1608c672ba2129b098a48e9e4d
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