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<li><a class="reference internal" href="#">Asynchronous Logging via PyZMQ</a><ul>
<li><a class="reference internal" href="#pub-sub-and-topics">PUB/SUB and Topics</a></li>
<li><a class="reference internal" href="#pubhandler">PUBHandler</a><ul>
<li><a class="reference internal" href="#subtopics">Subtopics</a></li>
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<div class="section" id="asynchronous-logging-via-pyzmq">
<span id="logging"></span><h1>Asynchronous Logging via PyZMQ<a class="headerlink" href="#asynchronous-logging-via-pyzmq" title="Permalink to this headline">¶</a></h1>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<ul class="last simple">
<li>The ØMQ guide <a class="reference external" href="http://zguide.zeromq.org/chapter:all#toc7">coverage</a> of PUB/SUB
messaging</li>
<li>Python logging module <a class="reference external" href="http://docs.python.org/library/logging.html">documentation</a></li>
</ul>
</div>
<p>Python provides extensible logging facilities through its <tt class="xref py py-mod docutils literal"><span class="pre">logging</span></tt> module. This
module allows for easily extensible logging functionality through the use of
<tt class="xref py py-class docutils literal"><span class="pre">Handler</span></tt> objects. The most obvious case for hooking up pyzmq to
logging would be to broadcast log messages over a PUB socket, so we have provides a
<a class="reference internal" href="api/generated/zmq.log.handlers.html#zmq.log.handlers.PUBHandler" title="zmq.log.handlers.PUBHandler"><tt class="xref py py-class docutils literal"><span class="pre">PUBHandler</span></tt></a> class for doing just that.</p>
<div class="section" id="pub-sub-and-topics">
<h2>PUB/SUB and Topics<a class="headerlink" href="#pub-sub-and-topics" title="Permalink to this headline">¶</a></h2>
<p>The ØMQ PUB/SUB pattern consists of a PUB socket broadcasting messages, and a collection
of SUB sockets that receive those messages. Each PUB message is a multipart-message, where
the first part is interpreted as a topic. SUB sockets can subscribe to topics by setting
their <tt class="docutils literal"><span class="pre">SUBSCRIBE</span></tt> sockopt, e.g.:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">sub</span> <span class="o">=</span> <span class="n">ctx</span><span class="o">.</span><span class="n">socket</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">sub</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">'topic1'</span><span class="p">)</span>
<span class="n">sub</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">'topic2'</span><span class="p">)</span>
</pre></div>
</div>
<p>When subscribed, the SUB socket will only receive messages where the first part <em>starts
with</em> one of the topics set via <tt class="docutils literal"><span class="pre">SUBSCRIBE</span></tt>. The default behavior is to exclude all
messages, and subscribing to the empty string ‘’ will receive all messages.</p>
</div>
<div class="section" id="pubhandler">
<h2>PUBHandler<a class="headerlink" href="#pubhandler" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="api/generated/zmq.log.handlers.html#zmq.log.handlers.PUBHandler" title="zmq.log.handlers.PUBHandler"><tt class="xref py py-class docutils literal"><span class="pre">PUBHandler</span></tt></a> object is created for allowing the python logging to be emitted
on a PUB socket. The main difference between a PUBHandler and a regular logging Handler is
the inclusion of topics. For the most basic logging, you can simply create a PUBHandler
with an interface or a configured PUB socket, and just let it go:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">pub</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">socket</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="n">pub</span><span class="o">.</span><span class="n">bind</span><span class="p">(</span><span class="s">'tcp://*:12345'</span><span class="p">)</span>
<span class="n">handler</span> <span class="o">=</span> <span class="n">PUBHandler</span><span class="p">(</span><span class="n">pub</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">logger</span><span class="o">.</span><span class="n">addHandler</span><span class="p">(</span><span class="n">handler</span><span class="p">)</span>
</pre></div>
</div>
<p>At this point, all messages logged with the default logger will be broadcast on the pub
socket.</p>
<p>the PUBHandler does work with topics, and the handler has an attribute <tt class="docutils literal"><span class="pre">root_topic</span></tt>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">handler</span><span class="o">.</span><span class="n">root_topic</span> <span class="o">=</span> <span class="s">'myprogram'</span>
</pre></div>
</div>
<p>Python loggers also have loglevels. The base topic of messages emitted by the PUBHandler
will be of the form: <tt class="docutils literal"><span class="pre"><handler.root_topic>.<loglevel></span></tt>, e.g. ‘myprogram.INFO’ or
‘whatever.ERROR’. This way, subscribers can easily subscribe to subsets of the logging
messages. Log messages are always two-part, where the first part is the topic tree, and
the second part is the actual log message.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">logger</span><span class="o">.</span><span class="n">info</span><span class="p">(</span><span class="s">'hello there'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">sub</span><span class="o">.</span><span class="n">recv_multipart</span><span class="p">()</span>
<span class="go">['myprogram.INFO', 'hello there']</span>
</pre></div>
</div>
<div class="section" id="subtopics">
<h3>Subtopics<a class="headerlink" href="#subtopics" title="Permalink to this headline">¶</a></h3>
<p>You can also add to the topic tree below the loglevel on an individual message basis.
Assuming your logger is connected to a PUBHandler, you can add as many additional topics
on the front of the message, which will be added always after the loglevel. A special
delimiter defined at <tt class="docutils literal"><span class="pre">zmq.log.handlers.TOPIC_DELIM</span></tt> is scanned by the PUBHandler, so if
you pass your own subtopics prior to that symbol, they will be stripped from the message
and added to the topic tree:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">log_msg</span> <span class="o">=</span> <span class="s">"hello there"</span>
<span class="gp">>>> </span><span class="n">subtopic</span> <span class="o">=</span> <span class="s">"sub.topic"</span>
<span class="gp">>>> </span><span class="n">msg</span> <span class="o">=</span> <span class="n">zmq</span><span class="o">.</span><span class="n">log</span><span class="o">.</span><span class="n">handlers</span><span class="o">.</span><span class="n">TOPIC_DELIM</span><span class="o">.</span><span class="n">join</span><span class="p">([</span><span class="n">subtopic</span><span class="p">,</span> <span class="n">log_msg</span><span class="p">])</span>
<span class="gp">>>> </span><span class="n">logger</span><span class="o">.</span><span class="n">warn</span><span class="p">(</span><span class="n">msg</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span> <span class="n">sub</span><span class="o">.</span><span class="n">recv_multipart</span><span class="p">()</span>
<span class="go">['myprogram.WARN.sub.topic', 'hello there']</span>
</pre></div>
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