<h1><spanclass="section-number">8. </span>Adding custom commands<aclass="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 <aclass="reference internal"href="../../../Components/Commands.html"><spanclass="doc std std-doc">Commands</span></a> 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>
An example is <codeclass="docutils literal notranslate"><spanclass="pre">look</span></code>, which examines your current location and tells you what it looks like and
<pclass="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 <codeclass="docutils literal notranslate"><spanclass="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
<aclass="reference internal"href="Beginner-Tutorial-Python-classes-and-objects.html"><spanclass="doc std std-doc">previous lesson about it</span></a>! A Command inherits from <codeclass="docutils literal notranslate"><spanclass="pre">evennia.Command</span></code> or from one of the alternative command- classes, such as <codeclass="docutils literal notranslate"><spanclass="pre">MuxCommand</span></code> which is what most default commands use.</p>
<p>All Commands are 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.</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. By default, Evennia groups all character-commands into one big cmdset called the <codeclass="docutils literal notranslate"><spanclass="pre">CharacterCmdSet</span></code>. It sits on <codeclass="docutils literal notranslate"><spanclass="pre">DefaultCharacter</span></code> (and thus, through inheritance, on <codeclass="docutils literal notranslate"><spanclass="pre">typeclasses.characters.Character</span></code>).</p>
<h2><spanclass="section-number">8.1. </span>Creating a custom command<aclass="headerlink"href="#creating-a-custom-command"title="Permalink to this headline">¶</a></h2>
<p>We can see that we import <codeclass="docutils literal notranslate"><spanclass="pre">Command</span></code> from <codeclass="docutils literal notranslate"><spanclass="pre">evennia</span></code> and use the <codeclass="docutils literal notranslate"><spanclass="pre">from</span><spanclass="pre">...</span><spanclass="pre">import</span><spanclass="pre">...</span><spanclass="pre">as</span><spanclass="pre">...</span></code> form to rename it to <codeclass="docutils literal notranslate"><spanclass="pre">BaseCommand</span></code>. This is so we can let our child class also be named <codeclass="docutils literal notranslate"><spanclass="pre">Command</span></code> to make it easier to reference. The class itself doesn’t do anything, it just has <codeclass="docutils literal notranslate"><spanclass="pre">pass</span></code>. So in the same way as <codeclass="docutils literal notranslate"><spanclass="pre">Object</span></code> and <codeclass="docutils literal notranslate"><spanclass="pre">Character</span></code> in the previous lessons, this class is identical to its parent.</p>
<div><p>The commented out <codeclass="docutils literal notranslate"><spanclass="pre">default_cmds</span></code> gives us access to Evennia’s default commands for easy overriding. We’ll try that a little later.</p>
<p>We could modify this module directly, but let’s work in a separate module just for the heck of it. Open a new file <codeclass="docutils literal notranslate"><spanclass="pre">mygame/commands/mycommands.py</span></code> and add the following code:</p>
<divclass="highlight-python notranslate"><divclass="highlight"><pre><span></span><spanclass="c1"># in mygame/commands/mycommands.py</span>
<p>Our <codeclass="docutils literal notranslate"><spanclass="pre">EchoCmdSet</span></code> class must have an <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">self.add()</span></code>. If you wanted to add more commands to this CmdSet you could just add more lines of <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">py</span></code> again:</p>
<p>The <codeclass="docutils literal notranslate"><spanclass="pre">me.cmdset</span></code> is the store of all cmdsets stored on us. By giving the path to our CmdSet class, it will be added.</p>
<p><codeclass="docutils literal notranslate"><spanclass="pre">echo</span></code> works! You should be getting a long list of outputs. The reason for this is that your <codeclass="docutils literal notranslate"><spanclass="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>
<p>These are all properties you can access with <codeclass="docutils literal notranslate"><spanclass="pre">.</span></code> on the Command instance, such as <codeclass="docutils literal notranslate"><spanclass="pre">.key</span></code>, <codeclass="docutils literal notranslate"><spanclass="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>
<li><p><codeclass="docutils literal notranslate"><spanclass="pre">args</span></code> - this is all arguments to the command. Now it’s empty, but if you tried <codeclass="docutils literal notranslate"><spanclass="pre">echo</span><spanclass="pre">foo</span><spanclass="pre">bar</span></code> you’d find that this would be <codeclass="docutils literal notranslate"><spanclass="pre">"</span><spanclass="pre">foo</span><spanclass="pre">bar"</span></code>.</p></li>
<li><p><codeclass="docutils literal notranslate"><spanclass="pre">obj</span></code> - this is object on which this Command (and CmdSet) “sits”. So you, in this case.</p></li>
<p>The reason our command doesn’t do anything yet is because it’s missing a <codeclass="docutils literal notranslate"><spanclass="pre">func</span></code> method. This is what Evennia looks for to figure out what a Command actually does. Modify your <codeclass="docutils literal notranslate"><spanclass="pre">CmdEcho</span></code> class:</p>
<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!</p>
<asideclass="sidebar">
<pclass="sidebar-title">Use Command.msg </p>
<p>In a Command class, the <codeclass="docutils literal notranslate"><spanclass="pre">self.msg()</span></code> acts as a convenient shortcut for <codeclass="docutils literal notranslate"><spanclass="pre">self.caller.msg()</span></code>. Not only is it shorter, it also has some advantages because the command can include more metadata with the message. So using <codeclass="docutils literal notranslate"><spanclass="pre">self.msg()</span></code> is usually better. For this tutorial though, <codeclass="docutils literal notranslate"><spanclass="pre">self.caller.msg()</span></code> is more explicit in showing what is going on.</p>
</aside>
<p>Next we add the <codeclass="docutils literal notranslate"><spanclass="pre">func</span></code> method. It has one active line where it makes use of some of those variables the Command class offers to us. If you did the <aclass="reference internal"href="Beginner-Tutorial-Python-basic-introduction.html"><spanclass="doc std std-doc">basic Python tutorial</span></a>, you will recognize <codeclass="docutils literal notranslate"><spanclass="pre">.msg</span></code> - this will send a message to the object it is attached to us - in this case <codeclass="docutils literal notranslate"><spanclass="pre">self.caller</span></code>, that is, us. We grab <codeclass="docutils literal notranslate"><spanclass="pre">self.args</span></code> and includes that in the message.</p>
<p>Since we haven’t changed <codeclass="docutils literal notranslate"><spanclass="pre">MyCmdSet</span></code>, that will work as before. Reload and re-add this command to ourselves to try out the new version:</p>
<p>Note that there is an extra space before <codeclass="docutils literal notranslate"><spanclass="pre">Woo!</span></code>. That is because self.args contains <em>everything</em> after the command name, including spaces. Evennia will happily understand if you skip that space too:</p>
<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>
<p>The only difference is that we called <codeclass="docutils literal notranslate"><spanclass="pre">.strip()</span></code> on <codeclass="docutils literal notranslate"><spanclass="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>
<h3><spanclass="section-number">8.1.1. </span>Making our cmdset persistent<aclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">echo</span></code> a <em>persistent</em> change though:</p>
<p>Now you can <codeclass="docutils literal notranslate"><spanclass="pre">reload</span></code> as much as you want and your code changes will be available directly without
<p>But for now, keep it around, we’ll expand it with some more examples.</p>
</section>
<sectionid="figuring-out-who-to-hit">
<h3><spanclass="section-number">8.1.2. </span>Figuring out who to hit<aclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">hit</span></code> command, for punching
someone in the face! This is how we want it to work:</p>
<divclass="highlight-none notranslate"><divclass="highlight"><pre><span></span>> hit <target>
<divclass="highlight-none notranslate"><divclass="highlight"><pre><span></span>You got hit by <hitter> with full force!
</pre></div>
</div>
<p>Here, <codeclass="docutils literal notranslate"><spanclass="pre"><hitter></span></code> would be the one using the <codeclass="docutils literal notranslate"><spanclass="pre">hit</span></code> command and <codeclass="docutils literal notranslate"><spanclass="pre"><target></span></code> is the one doing the punching.</p>
<p>Still in <codeclass="docutils literal notranslate"><spanclass="pre">mygame/commands/mycommands.py</span></code>, add a new class, between <codeclass="docutils literal notranslate"><spanclass="pre">CmdEcho</span></code> and <codeclass="docutils literal notranslate"><spanclass="pre">MyCmdSet</span></code>.</p>
<spanclass="bp">self</span><spanclass="o">.</span><spanclass="n">caller</span><spanclass="o">.</span><spanclass="n">msg</span><spanclass="p">(</span><spanclass="s2">"Who do you want to hit?"</span><spanclass="p">)</span>
<spanclass="bp">self</span><spanclass="o">.</span><spanclass="n">caller</span><spanclass="o">.</span><spanclass="n">msg</span><spanclass="p">(</span><spanclass="sa">f</span><spanclass="s2">"You hit </span><spanclass="si">{</span><spanclass="n">target</span><spanclass="o">.</span><spanclass="n">key</span><spanclass="si">}</span><spanclass="s2"> with full force!"</span><spanclass="p">)</span>
<spanclass="n">target</span><spanclass="o">.</span><spanclass="n">msg</span><spanclass="p">(</span><spanclass="sa">f</span><spanclass="s2">"You got hit by </span><spanclass="si">{</span><spanclass="bp">self</span><spanclass="o">.</span><spanclass="n">caller</span><spanclass="o">.</span><spanclass="n">key</span><spanclass="si">}</span><spanclass="s2"> with full force!"</span><spanclass="p">)</span>
<spanclass="c1"># ...</span>
</pre></div></td></tr></table></div>
</div>
<p>A lot of things to dissect here:</p>
<ulclass="simple">
<li><p><strong>Line 3</strong>: The normal <codeclass="docutils literal notranslate"><spanclass="pre">class</span></code> header. We inherit from <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="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
<codeclass="docutils literal notranslate"><spanclass="pre">self.args.strip()</span></code> over and over, we store the stripped version
in a <em>local variable</em><codeclass="docutils literal notranslate"><spanclass="pre">args</span></code>. Note that we don’t modify <codeclass="docutils literal notranslate"><spanclass="pre">self.args</span></code> by doing this, <codeclass="docutils literal notranslate"><spanclass="pre">self.args</span></code> will still
have the whitespace and is not the same as <codeclass="docutils literal notranslate"><spanclass="pre">args</span></code> in this example.</p></li>
<p>There can be any number of <codeclass="docutils literal notranslate"><spanclass="pre">elifs</span></code> to mark when different branches of the code should run. If
the <codeclass="docutils literal notranslate"><spanclass="pre">else</span></code> condition is given, it will run if none of the other conditions was truthy. In Python
the <codeclass="docutils literal notranslate"><spanclass="pre">if..elif..else</span></code> structure also serves the same function as <codeclass="docutils literal notranslate"><spanclass="pre">case</span></code> in some other languages.</p>
<li><p><strong>Line 15</strong> has our first <em>conditional</em>, an <codeclass="docutils literal notranslate"><spanclass="pre">if</span></code> statement. This is written on the form <codeclass="docutils literal notranslate"><spanclass="pre">if</span><spanclass="pre"><condition>:</span></code> and only if that condition is ‘truthy’ will the indented code block under the <codeclass="docutils literal notranslate"><spanclass="pre">if</span></code> statement run. To learn what is truthy in Python it’s usually easier to learn what is “falsy”:</p>
<li><p><codeclass="docutils literal notranslate"><spanclass="pre">False</span></code> - this is a reserved boolean word in Python. The opposite is <codeclass="docutils literal notranslate"><spanclass="pre">True</span></code>.</p></li>
<li><p><codeclass="docutils literal notranslate"><spanclass="pre">None</span></code> - another reserved word. This represents nothing, a null-result or value.</p></li>
<li><p><codeclass="docutils literal notranslate"><spanclass="pre">0</span></code> or <codeclass="docutils literal notranslate"><spanclass="pre">0.0</span></code></p></li>
<li><p>The empty string <codeclass="docutils literal notranslate"><spanclass="pre">""</span></code> or <codeclass="docutils literal notranslate"><spanclass="pre">''</span></code> or <codeclass="docutils literal notranslate"><spanclass="pre">""""""</span></code> or <codeclass="docutils literal notranslate"><spanclass="pre">''''''</span></code></p></li>
<li><p>Empty <em>iterables</em> we haven’t seen yet, like empty lists <codeclass="docutils literal notranslate"><spanclass="pre">[]</span></code>, empty tuples <codeclass="docutils literal notranslate"><spanclass="pre">()</span></code> and empty dicts <codeclass="docutils literal notranslate"><spanclass="pre">{}</span></code>.</p></li>
<li><p><strong>Line 16</strong>’s condition is <codeclass="docutils literal notranslate"><spanclass="pre">not</span><spanclass="pre">args</span></code>. The <codeclass="docutils literal notranslate"><spanclass="pre">not</span></code><em>inverses</em> the result, so if <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">if</span></code> statement is truthy, in this case if <codeclass="docutils literal notranslate"><spanclass="pre">args</span></code> is the empty string.</p></li>
<li><p><strong>Line 17</strong>: <codeclass="docutils literal notranslate"><spanclass="pre">return</span></code> is a reserved Python word that exits <codeclass="docutils literal notranslate"><spanclass="pre">func</span></code> immediately.</p></li>
<li><p><strong>Line 18</strong>: We use <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">.search</span></code> is that it will already inform <codeclass="docutils literal notranslate"><spanclass="pre">self.caller</span></code> if it couldn’t find the target. In that case, <codeclass="docutils literal notranslate"><spanclass="pre">target</span></code> will be <codeclass="docutils literal notranslate"><spanclass="pre">None</span></code> and we should just directly <codeclass="docutils literal notranslate"><spanclass="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 <codeclass="docutils literal notranslate"><spanclass="pre">MyCmdSet</span></code> which we made persistent earlier.</p>
<p>With longer code snippets to try, it gets more and more likely you’ll
make an error and get a <codeclass="docutils literal notranslate"><spanclass="pre">traceback</span></code> when you reload. This will either appear
directly in-game or in your log (view it with <codeclass="docutils literal notranslate"><spanclass="pre">evennia</span><spanclass="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 <aclass="reference internal"href="Beginner-Tutorial-Python-basic-introduction.html"><spanclass="doc std std-doc">The Python introduction lesson</span></a> for more hints. If you get stuck, reach out to the Evennia community for help.</p>
