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<div class="section" id="weather-tutorial">
<h1>Weather Tutorial<a class="headerlink" href="#weather-tutorial" title="Permalink to this headline"></a></h1>
<p>This tutorial will have us create a simple weather system for our MUD. The way we want to use this is to have all outdoor rooms echo weather-related messages to the room at regular and semi-random intervals. Things like “Clouds gather above”, “It starts to rain” and so on.</p>
<p>One could imagine every outdoor room in the game having a script running on themselves that fires regularly. For this particular example it is however more efficient to do it another way, namely by using a “ticker-subscription” model. The principle is simple: Instead of having each Object individually track the time, they instead subscribe to be called by a global ticker who handles time keeping. Not only does this centralize and organize much of the code in one place, it also has less computing overhead.</p>
<p>Evennia offers the <a class="reference internal" href="TickerHandler.html"><span class="doc">TickerHandler</span></a> specifically for using the subscription model. We will use it for our weather system.</p>
<p>We will assume you know how to make your own Typeclasses. If not see one of the beginning tutorials. We will create a new WeatherRoom typeclass that is aware of the day-night cycle.</p>
<div class="highlight-python notranslate"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre> 1
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21</pre></div></td><td class="code"><div class="highlight"><pre><span></span>
<span class="kn">import</span> <span class="nn">random</span>
<span class="kn">from</span> <span class="nn">evennia</span> <span class="kn">import</span> <span class="n">DefaultRoom</span><span class="p">,</span> <span class="n">TICKER_HANDLER</span>
<span class="n">ECHOES</span> <span class="o">=</span> <span class="p">[</span><span class="s2">&quot;The sky is clear.&quot;</span><span class="p">,</span>
<span class="s2">&quot;Clouds gather overhead.&quot;</span><span class="p">,</span>
<span class="s2">&quot;It&#39;s starting to drizzle.&quot;</span><span class="p">,</span>
<span class="s2">&quot;A breeze of wind is felt.&quot;</span><span class="p">,</span>
<span class="s2">&quot;The wind is picking up&quot;</span><span class="p">]</span> <span class="c1"># etc </span>
<span class="k">class</span> <span class="nc">WeatherRoom</span><span class="p">(</span><span class="n">DefaultRoom</span><span class="p">):</span>
<span class="s2">&quot;This room is ticked at regular intervals&quot;</span>
<span class="k">def</span> <span class="nf">at_object_creation</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="s2">&quot;called only when the object is first created&quot;</span>
<span class="n">TICKER_HANDLER</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="mi">60</span> <span class="o">*</span> <span class="mi">60</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">at_weather_update</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">at_weather_update</span><span class="p">(</span><span class="bp">self</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="s2">&quot;ticked at regular intervals&quot;</span>
<span class="n">echo</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">ECHOES</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">msg_contents</span><span class="p">(</span><span class="n">echo</span><span class="p">)</span>
</pre></div>
</td></tr></table></div>
<p>In the <code class="docutils literal notranslate"><span class="pre">at_object_creation</span></code> method, we simply added ourselves to the TickerHandler and tell it to call <code class="docutils literal notranslate"><span class="pre">at_weather_update</span></code> every hour (<code class="docutils literal notranslate"><span class="pre">60*60</span></code> seconds). During testing you might want to play with a shorter time duration.</p>
<p>For this to work we also create a custom hook <code class="docutils literal notranslate"><span class="pre">at_weather_update(*args,</span> <span class="pre">**kwargs)</span></code>, which is the call sign required by TickerHandler hooks.</p>
<p>Henceforth the room will inform everyone inside it when the weather changes. This particular example is of course very simplistic - the weather echoes are just randomly chosen and dont care what weather came before it. Expanding it to be more realistic is a useful exercise.</p>
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