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<section class="tex2jax_ignore mathjax_ignore" id="adding-custom-commands">
<h1><span class="section-number">8. </span>Adding custom commands<a class="headerlink" href="#adding-custom-commands" title="Permalink to this headline"></a></h1>
<p>In this lesson we’ll learn how to create our own Evennia <em>Commands</em>. If you are new to Python you’ll
also learn some more basics about how to manipulate strings and get information out of Evennia.</p>
<p>A Command is something that handles the input from a user and causes a result to happen.
An example is <code class="docutils literal notranslate"><span class="pre">look</span></code>, which examines your current location and tells how it looks like and
what is in it.</p>
<aside class="sidebar">
<p class="sidebar-title">Commands are not typeclassed</p>
<p>If you just came from the previous lesson, you might want to know that Commands and
CommandSets are not <code class="docutils literal notranslate"><span class="pre">typeclassed</span></code>. That is, instances of them are not saved to the
database. They are “just” normal Python classes.</p>
</aside>
<p>In Evennia, a Command is a Python <em>class</em>. If you are unsure about what a class is, review the
previous lessons! A Command inherits from <code class="docutils literal notranslate"><span class="pre">evennia.Command</span></code> or from one of the alternative command-
classes, such as <code class="docutils literal notranslate"><span class="pre">MuxCommand</span></code> which is what most default commands use.</p>
<p>All Commands are in turn grouped in another class called a <em>Command Set</em>. Think of a Command Set
as a bag holding many different commands. One CmdSet could for example hold all commands for
combat, another for building etc. By default, Evennia groups all character-commands into one
big cmdset.</p>
<p>Command-Sets are then associated with objects, for example with your Character. Doing so makes the
commands in that cmdset available to the object. So, to summarize:</p>
<ul class="simple">
<li><p>Commands are classes</p></li>
<li><p>A group of Commands is stored in a CmdSet</p></li>
<li><p>CmdSets are stored on objects - this defines which commands are available to that object.</p></li>
</ul>
<section id="creating-a-custom-command">
<h2><span class="section-number">8.1. </span>Creating a custom command<a class="headerlink" href="#creating-a-custom-command" title="Permalink to this headline"></a></h2>
<p>Open <code class="docutils literal notranslate"><span class="pre">mygame/commands/command.py</span></code>:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd">(module docstring)</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="kn">from</span> <span class="nn">evennia</span> <span class="kn">import</span> <span class="n">Command</span> <span class="k">as</span> <span class="n">BaseCommand</span>
<span class="c1"># from evennia import default_cmds</span>
<span class="k">class</span> <span class="nc">Command</span><span class="p">(</span><span class="n">BaseCommand</span><span class="p">):</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> (class docstring)</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="k">pass</span>
<span class="c1"># (lots of commented-out stuff)</span>
<span class="c1"># ...</span>
</pre></div>
</div>
<p>Ignoring the docstrings (which you can read if you want), this is the only really active code in the module.</p>
<p>We can see that we import <code class="docutils literal notranslate"><span class="pre">Command</span></code> from <code class="docutils literal notranslate"><span class="pre">evennia</span></code> and use the <code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">...</span> <span class="pre">import</span> <span class="pre">...</span> <span class="pre">as</span> <span class="pre">...</span></code> form to rename it
to <code class="docutils literal notranslate"><span class="pre">BaseCommand</span></code>. This is so we can let our child class also be named <code class="docutils literal notranslate"><span class="pre">Command</span></code> for reference. The class
itself doesn’t do anything, it just has <code class="docutils literal notranslate"><span class="pre">pass</span></code>. So in the same way as <code class="docutils literal notranslate"><span class="pre">Object</span></code> in the previous lesson, this
class is identical to its parent.</p>
<blockquote>
<div><p>The commented out <code class="docutils literal notranslate"><span class="pre">default_cmds</span></code> gives us access to Evennia’s default commands for easy overriding. We’ll try
that a little later.</p>
</div></blockquote>
<p>We could modify this module directly, but to train imports we’ll work in a separate module. Open a new file
<code class="docutils literal notranslate"><span class="pre">mygame/commands/mycommands.py</span></code> and add the following code:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span>
<span class="kn">from</span> <span class="nn">commands.command</span> <span class="kn">import</span> <span class="n">Command</span>
<span class="k">class</span> <span class="nc">CmdEcho</span><span class="p">(</span><span class="n">Command</span><span class="p">):</span>
<span class="n">key</span> <span class="o">=</span> <span class="s2">&quot;echo&quot;</span>
</pre></div>
</div>
<p>This is the simplest form of command you can imagine. It just gives itself a name, “echo”. This is
what you will use to call this command later.</p>
<p>Next we need to put this in a CmdSet. It will be a one-command CmdSet for now! Change your file as such:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span>
<span class="kn">from</span> <span class="nn">commands.command</span> <span class="kn">import</span> <span class="n">Command</span>
<span class="kn">from</span> <span class="nn">evennia</span> <span class="kn">import</span> <span class="n">CmdSet</span>
<span class="k">class</span> <span class="nc">CmdEcho</span><span class="p">(</span><span class="n">Command</span><span class="p">):</span>
<span class="n">key</span> <span class="o">=</span> <span class="s2">&quot;echo&quot;</span>
<span class="k">class</span> <span class="nc">MyCmdSet</span><span class="p">(</span><span class="n">CmdSet</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">at_cmdset_creation</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">add</span><span class="p">(</span><span class="n">CmdEcho</span><span class="p">)</span>
</pre></div>
</div>
<p>Our <code class="docutils literal notranslate"><span class="pre">EchoCmdSet</span></code> class must have an <code class="docutils literal notranslate"><span class="pre">at_cmdset_creation</span></code> method, named exactly
like this - this is what Evennia will be looking for when setting up the cmdset later, so
if you didn’t set it up, it will use the parent’s version, which is empty. Inside we add the
command class to the cmdset by <code class="docutils literal notranslate"><span class="pre">self.add()</span></code>. If you wanted to add more commands to this CmdSet you
could just add more lines of <code class="docutils literal notranslate"><span class="pre">self.add</span></code> after this.</p>
<p>Finally, let’s add this command to ourselves so we can try it out. In-game you can experiment with <code class="docutils literal notranslate"><span class="pre">py</span></code> again:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; py self.cmdset.add(&quot;commands.mycommands.MyCmdSet&quot;)
</pre></div>
</div>
<p>Now try</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; echo
Command echo has no defined `func()` - showing on-command variables:
...
...
</pre></div>
</div>
<p>You should be getting a long list of outputs. The reason for this is that your <code class="docutils literal notranslate"><span class="pre">echo</span></code> function is not really
“doing” anything yet and the default function is then to show all useful resources available to you when you
use your Command. Let’s look at some of those listed:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Command echo has no defined `func()` - showing on-command variables:
obj (&lt;class &#39;typeclasses.characters.Character&#39;&gt;): YourName
lockhandler (&lt;class &#39;evennia.locks.lockhandler.LockHandler&#39;&gt;): cmd:all()
caller (&lt;class &#39;typeclasses.characters.Character&#39;&gt;): YourName
cmdname (&lt;class &#39;str&#39;&gt;): echo
raw_cmdname (&lt;class &#39;str&#39;&gt;): echo
cmdstring (&lt;class &#39;str&#39;&gt;): echo
args (&lt;class &#39;str&#39;&gt;):
cmdset (&lt;class &#39;evennia.commands.cmdset.CmdSet&#39;&gt;): @mail, about, access, accounts, addcom, alias, allcom, ban, batchcode, batchcommands, boot, cboot, ccreate,
cdesc, cdestroy, cemit, channels, charcreate, chardelete, checklockstring, clientwidth, clock, cmdbare, cmdsets, color, copy, cpattr, create, cwho, delcom,
desc, destroy, dig, dolphin, drop, echo, emit, examine, find, force, get, give, grapevine2chan, help, home, ic, inventory, irc2chan, ircstatus, link, lock,
look, menutest, mudinfo, mvattr, name, nick, objects, ooc, open, option, page, password, perm, pose, public, py, quell, quit, reload, reset, rss2chan, say,
script, scripts, server, service, sessions, set, setdesc, sethelp, sethome, shutdown, spawn, style, tag, tel, test2010, test2028, testrename, testtable,
tickers, time, tunnel, typeclass, unban, unlink, up, up, userpassword, wall, whisper, who, wipe
session (&lt;class &#39;evennia.server.serversession.ServerSession&#39;&gt;): Griatch(#1)@1:2:7:.:0:.:0:.:1
account (&lt;class &#39;typeclasses.accounts.Account&#39;&gt;): Griatch(account 1)
raw_string (&lt;class &#39;str&#39;&gt;): echo
--------------------------------------------------
echo - Command variables from evennia:
--------------------------------------------------
name of cmd (self.key): echo
cmd aliases (self.aliases): []
cmd locks (self.locks): cmd:all();
help category (self.help_category): General
object calling (self.caller): Griatch
object storing cmdset (self.obj): Griatch
command string given (self.cmdstring): echo
current cmdset (self.cmdset): ChannelCmdSet
</pre></div>
</div>
<p>These are all properties you can access with <code class="docutils literal notranslate"><span class="pre">.</span></code> on the Command instance, such as <code class="docutils literal notranslate"><span class="pre">.key</span></code>, <code class="docutils literal notranslate"><span class="pre">.args</span></code> and so on.
Evennia makes these available to you and they will be different every time a command is run. The most
important ones we will make use of now are:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">caller</span></code> - this is ‘you’, the person calling the command.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">args</span></code> - this is all arguments to the command. Now it’s empty, but if you tried <code class="docutils literal notranslate"><span class="pre">echo</span> <span class="pre">foo</span> <span class="pre">bar</span></code> you’d find
that this would be <code class="docutils literal notranslate"><span class="pre">&quot;</span> <span class="pre">foo</span> <span class="pre">bar&quot;</span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">obj</span></code> - this is object on which this Command (and CmdSet) “sits”. So you, in this case.</p></li>
</ul>
<p>The reason our command doesn’t do anything yet is because it’s missing a <code class="docutils literal notranslate"><span class="pre">func</span></code> method. This is what Evennia
looks for to figure out what a Command actually does. Modify your <code class="docutils literal notranslate"><span class="pre">CmdEcho</span></code> class:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># ...</span>
<span class="k">class</span> <span class="nc">CmdEcho</span><span class="p">(</span><span class="n">Command</span><span class="p">):</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> A simple echo command</span>
<span class="sd"> Usage:</span>
<span class="sd"> echo &lt;something&gt;</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="n">key</span> <span class="o">=</span> <span class="s2">&quot;echo&quot;</span>
<span class="k">def</span> <span class="nf">func</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">caller</span><span class="o">.</span><span class="n">msg</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Echo: &#39;</span><span class="si">{</span><span class="bp">self</span><span class="o">.</span><span class="n">args</span><span class="si">}</span><span class="s2">&#39;&quot;</span><span class="p">)</span>
<span class="c1"># ...</span>
</pre></div>
</div>
<p>First we added a docstring. This is always a good thing to do in general, but for a Command class, it will also
automatically become the in-game help entry! Next we add the <code class="docutils literal notranslate"><span class="pre">func</span></code> method. It has one active line where it
makes use of some of those variables we found the Command offers to us. If you did the
<a class="reference internal" href="Python-basic-introduction.html"><span class="doc std std-doc">basic Python tutorial</span></a>, you will recognize <code class="docutils literal notranslate"><span class="pre">.msg</span></code> - this will send a message
to the object it is attached to us - in this case <code class="docutils literal notranslate"><span class="pre">self.caller</span></code>, that is, us. We grab <code class="docutils literal notranslate"><span class="pre">self.args</span></code> and includes
that in the message.</p>
<p>Since we haven’t changed <code class="docutils literal notranslate"><span class="pre">MyCmdSet</span></code>, that will work as before. Reload and re-add this command to ourselves to
try out the new version:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; reload
&gt; py self.cmdset.add(&quot;commands.mycommands.MyCmdSet&quot;)
&gt; echo
Echo: &#39;&#39;
</pre></div>
</div>
<p>Try to pass an argument:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; echo Woo Tang!
Echo: &#39; Woo Tang!&#39;
</pre></div>
</div>
<p>Note that there is an extra space before <code class="docutils literal notranslate"><span class="pre">Woo!</span></code>. That is because self.args contains the <em>everything</em> after
the command name, including spaces. Evennia will happily understand if you skip that space too:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; echoWoo Tang!
Echo: &#39;Woo Tang!&#39;
</pre></div>
</div>
<p>There are ways to force Evennia to <em>require</em> an initial space, but right now we want to just ignore it since
it looks a bit weird for our echo example. Tweak the code:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># ...</span>
<span class="k">class</span> <span class="nc">CmdEcho</span><span class="p">(</span><span class="n">Command</span><span class="p">):</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> A simple echo command</span>
<span class="sd"> Usage:</span>
<span class="sd"> echo &lt;something&gt;</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="n">key</span> <span class="o">=</span> <span class="s2">&quot;echo&quot;</span>
<span class="k">def</span> <span class="nf">func</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">caller</span><span class="o">.</span><span class="n">msg</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Echo: &#39;</span><span class="si">{</span><span class="bp">self</span><span class="o">.</span><span class="n">args</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span><span class="si">}</span><span class="s2">&#39;&quot;</span><span class="p">)</span>
<span class="c1"># ...</span>
</pre></div>
</div>
<p>The only difference is that we called <code class="docutils literal notranslate"><span class="pre">.strip()</span></code> on <code class="docutils literal notranslate"><span class="pre">self.args</span></code>. This is a helper method available on all
strings - it strips out all whitespace before and after the string. Now the Command-argument will no longer
have any space in front of it.</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; reload
&gt; py self.cmdset.add(&quot;commands.mycommands.MyCmdSet&quot;)
&gt; echo Woo Tang!
Echo: &#39;Woo Tang!&#39;
</pre></div>
</div>
<p>Don’t forget to look at the help for the echo command:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; help echo
</pre></div>
</div>
<p>You will get the docstring you put in your Command-class.</p>
<section id="making-our-cmdset-persistent">
<h3><span class="section-number">8.1.1. </span>Making our cmdset persistent<a class="headerlink" href="#making-our-cmdset-persistent" title="Permalink to this headline"></a></h3>
<p>It’s getting a little annoying to have to re-add our cmdset every time we reload, right? It’s simple
enough to make <code class="docutils literal notranslate"><span class="pre">echo</span></code> a <em>persistent</em> change though:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; py self.cmdset.add(&quot;commands.mycommands.MyCmdSet&quot;, persistent=True)
</pre></div>
</div>
<p>Now you can <code class="docutils literal notranslate"><span class="pre">reload</span></code> as much as you want and your code changes will be available directly without
needing to re-add the MyCmdSet again. To remove the cmdset again, do</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; py self.cmdset.remove(&quot;commands.mycommands.MyCmdSet&quot;)
</pre></div>
</div>
<p>But for now, keep it around, we’ll expand it with some more examples.</p>
</section>
<section id="figuring-out-who-to-hit">
<h3><span class="section-number">8.1.2. </span>Figuring out who to hit<a class="headerlink" href="#figuring-out-who-to-hit" title="Permalink to this headline"></a></h3>
<p>Let’s try something a little more exciting than just echo. Let’s make a <code class="docutils literal notranslate"><span class="pre">hit</span></code> command, for punching
someone in the face! This is how we want it to work:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; hit &lt;target&gt;
You hit &lt;target&gt; with full force!
</pre></div>
</div>
<p>Not only that, we want the <target> to see</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>You got hit by &lt;hitter&gt; with full force!
</pre></div>
</div>
<p>Here, <code class="docutils literal notranslate"><span class="pre">&lt;hitter&gt;</span></code> would be the one using the <code class="docutils literal notranslate"><span class="pre">hit</span></code> command and <code class="docutils literal notranslate"><span class="pre">&lt;target&gt;</span></code> is the one doing the punching.</p>
<p>Still in <code class="docutils literal notranslate"><span class="pre">mygame/commands/mycommands.py</span></code>, add a new class, between <code class="docutils literal notranslate"><span class="pre">CmdEcho</span></code> and <code class="docutils literal notranslate"><span class="pre">MyCmdSet</span></code>.</p>
<div class="highlight-python notranslate"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal"> 1</span>
<span class="normal"> 2</span>
<span class="normal"> 3</span>
<span class="normal"> 4</span>
<span class="normal"> 5</span>
<span class="normal"> 6</span>
<span class="normal"> 7</span>
<span class="normal"> 8</span>
<span class="normal"> 9</span>
<span class="normal">10</span>
<span class="normal">11</span>
<span class="normal">12</span>
<span class="normal">13</span>
<span class="normal">14</span>
<span class="normal">15</span>
<span class="normal">16</span>
<span class="normal">17</span>
<span class="normal">18</span>
<span class="normal">19</span>
<span class="normal">20</span>
<span class="normal">21</span>
<span class="normal">22</span>
<span class="normal">23</span></pre></div></td><td class="code"><div><pre><span></span><span class="c1"># ...</span>
<span class="k">class</span> <span class="nc">CmdHit</span><span class="p">(</span><span class="n">Command</span><span class="p">):</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> Hit a target.</span>
<span class="sd"> Usage:</span>
<span class="sd"> hit &lt;target&gt;</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="n">key</span> <span class="o">=</span> <span class="s2">&quot;hit&quot;</span>
<span class="k">def</span> <span class="nf">func</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">args</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">args</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">args</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">caller</span><span class="o">.</span><span class="n">msg</span><span class="p">(</span><span class="s2">&quot;Who do you want to hit?&quot;</span><span class="p">)</span>
<span class="k">return</span>
<span class="n">target</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">caller</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">target</span><span class="p">:</span>
<span class="k">return</span>
<span class="bp">self</span><span class="o">.</span><span class="n">caller</span><span class="o">.</span><span class="n">msg</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;You hit </span><span class="si">{</span><span class="n">target</span><span class="o">.</span><span class="n">key</span><span class="si">}</span><span class="s2"> with full force!&quot;</span><span class="p">)</span>
<span class="n">target</span><span class="o">.</span><span class="n">msg</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;You got hit by </span><span class="si">{</span><span class="bp">self</span><span class="o">.</span><span class="n">caller</span><span class="o">.</span><span class="n">key</span><span class="si">}</span><span class="s2"> with full force!&quot;</span><span class="p">)</span>
<span class="c1"># ...</span>
</pre></div></td></tr></table></div>
</div>
<p>A lot of things to dissect here:</p>
<ul class="simple">
<li><p><strong>Line 3</strong>: The normal <code class="docutils literal notranslate"><span class="pre">class</span></code> header. We inherit from <code class="docutils literal notranslate"><span class="pre">Command</span></code> which we imported at the top of this file.</p></li>
<li><p><strong>Lines 4-10</strong>: The docstring and help-entry for the command. You could expand on this as much as you wanted.</p></li>
<li><p><strong>Line 11</strong>: We want to write <code class="docutils literal notranslate"><span class="pre">hit</span></code> to use this command.</p></li>
<li><p><strong>Line 14</strong>: We strip the whitespace from the argument like before. Since we don’t want to have to do
<code class="docutils literal notranslate"><span class="pre">self.args.strip()</span></code> over and over, we store the stripped version
in a <em>local variable</em> <code class="docutils literal notranslate"><span class="pre">args</span></code>. Note that we don’t modify <code class="docutils literal notranslate"><span class="pre">self.args</span></code> by doing this, <code class="docutils literal notranslate"><span class="pre">self.args</span></code> will still
have the whitespace and is not the same as <code class="docutils literal notranslate"><span class="pre">args</span></code> in this example.</p></li>
</ul>
<aside class="sidebar">
<p class="sidebar-title">if-statements</p>
<p>The full form of the if statement is</p>
<p>if condition:
…
elif othercondition:
…
else:
…</p>
<p>There can be any number of <code class="docutils literal notranslate"><span class="pre">elifs</span></code> to mark when different branches of the code should run. If
the <code class="docutils literal notranslate"><span class="pre">else</span></code> condition is given, it will run if none of the other conditions was truthy. In Python
the <code class="docutils literal notranslate"><span class="pre">if..elif..else</span></code> structure also serves the same function as <code class="docutils literal notranslate"><span class="pre">case</span></code> in some other languages.</p>
</aside>
<ul>
<li><p><strong>Line 15</strong> has our first <em>conditional</em>, an <code class="docutils literal notranslate"><span class="pre">if</span></code> statement. This is written on the form <code class="docutils literal notranslate"><span class="pre">if</span> <span class="pre">&lt;condition&gt;:</span></code> and only
if that condition is ‘truthy’ will the indented code block under the <code class="docutils literal notranslate"><span class="pre">if</span></code> statement run. To learn what is truthy in
Python it’s usually easier to learn what is “falsy”:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">False</span></code> - this is a reserved boolean word in Python. The opposite is <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">None</span></code> - another reserved word. This represents nothing, a null-result or value.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">0</span></code> or <code class="docutils literal notranslate"><span class="pre">0.0</span></code></p></li>
<li><p>The empty string <code class="docutils literal notranslate"><span class="pre">&quot;&quot;</span></code> or <code class="docutils literal notranslate"><span class="pre">''</span></code> or <code class="docutils literal notranslate"><span class="pre">&quot;&quot;&quot;&quot;&quot;&quot;</span></code> or <code class="docutils literal notranslate"><span class="pre">''''''</span></code></p></li>
<li><p>Empty <em>iterables</em> we haven’t seen yet, like empty lists <code class="docutils literal notranslate"><span class="pre">[]</span></code>, empty tuples <code class="docutils literal notranslate"><span class="pre">()</span></code> and empty dicts <code class="docutils literal notranslate"><span class="pre">{}</span></code>.</p></li>
<li><p>Everything else is “truthy”.</p></li>
</ul>
<p>Line 16’s condition is <code class="docutils literal notranslate"><span class="pre">not</span> <span class="pre">args</span></code>. The <code class="docutils literal notranslate"><span class="pre">not</span></code> <em>inverses</em> the result, so if <code class="docutils literal notranslate"><span class="pre">args</span></code> is the empty string (falsy), the
whole conditional becomes truthy. Let’s continue in the code:</p>
</li>
<li><p><strong>Lines 16-17</strong>: This code will only run if the <code class="docutils literal notranslate"><span class="pre">if</span></code> statement is truthy, in this case if <code class="docutils literal notranslate"><span class="pre">args</span></code> is the empty string.</p></li>
<li><p><strong>Line 17</strong>: <code class="docutils literal notranslate"><span class="pre">return</span></code> is a reserved Python word that exits <code class="docutils literal notranslate"><span class="pre">func</span></code> immediately.</p></li>
<li><p><strong>Line 18</strong>: We use <code class="docutils literal notranslate"><span class="pre">self.caller.search</span></code> to look for the target in the current location.</p></li>
<li><p><strong>Lines 19-20</strong>: A feature of <code class="docutils literal notranslate"><span class="pre">.search</span></code> is that it will already inform <code class="docutils literal notranslate"><span class="pre">self.caller</span></code> if it couldn’t find the target.
In that case, <code class="docutils literal notranslate"><span class="pre">target</span></code> will be <code class="docutils literal notranslate"><span class="pre">None</span></code> and we should just directly <code class="docutils literal notranslate"><span class="pre">return</span></code>.</p></li>
<li><p><strong>Lines 21-22</strong>: At this point we have a suitable target and can send our punching strings to each.</p></li>
</ul>
<p>Finally we must also add this to a CmdSet. Let’s add it to <code class="docutils literal notranslate"><span class="pre">MyCmdSet</span></code> which we made persistent earlier.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># ...</span>
<span class="k">class</span> <span class="nc">MyCmdSet</span><span class="p">(</span><span class="n">CmdSet</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">at_cmdset_creation</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">add</span><span class="p">(</span><span class="n">CmdEcho</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">CmdHit</span><span class="p">)</span>
</pre></div>
</div>
<aside class="sidebar">
<p class="sidebar-title">Errors in your code</p>
<p>With longer code snippets to try, it gets more and more likely you’ll
make an error and get a <code class="docutils literal notranslate"><span class="pre">traceback</span></code> when you reload. This will either appear
directly in-game or in your log (view it with <code class="docutils literal notranslate"><span class="pre">evennia</span> <span class="pre">-l</span></code> in a terminal).
Don’t panic; tracebacks are your friends - they are to be read bottom-up and usually describe
exactly where your problem is. Refer to <code class="docutils literal notranslate"><span class="pre">The</span> <span class="pre">Python</span> <span class="pre">intro</span> <span class="pre">&lt;Python-basic-introduction.html&gt;</span></code>_ for
more hints. If you get stuck, reach out to the Evennia community for help.</p>
</aside>
<p>Next we reload to let Evennia know of these code changes and try it out:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>&gt; reload
hit
Who do you want to hit?
hit me
You hit YourName with full force!
You got hit by YourName with full force!
</pre></div>
</div>
<p>Lacking a target, we hit ourselves. If you have one of the dragons still around from the previous lesson
you could try to hit it (if you dare):</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>hit smaug
You hit Smaug with full force!
</pre></div>
</div>
<p>You won’t see the second string. Only Smaug sees that (and is not amused).</p>
</section>
</section>
<section id="summary">
<h2><span class="section-number">8.2. </span>Summary<a class="headerlink" href="#summary" title="Permalink to this headline"></a></h2>
<p>In this lesson we learned how to create our own Command, add it to a CmdSet and then to ourselves.
We also upset a dragon.</p>
<p>In the next lesson we’ll learn how to hit Smaug with different weapons. We’ll also
get into how we replace and extend Evennia’s default Commands.</p>
</section>
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<p><h3><a href="../../../index.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">8. Adding custom commands</a><ul>
<li><a class="reference internal" href="#creating-a-custom-command">8.1. Creating a custom command</a><ul>
<li><a class="reference internal" href="#making-our-cmdset-persistent">8.1.1. Making our cmdset persistent</a></li>
<li><a class="reference internal" href="#figuring-out-who-to-hit">8.1.2. Figuring out who to hit</a></li>
</ul>
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<li><a class="reference internal" href="#summary">8.2. Summary</a></li>
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<h4>Next topic</h4>
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title="next chapter"><span class="section-number">9. </span>Parsing Command input</a></p>
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