<h1>Building a giant mech<aclass="headerlink"href="#building-a-giant-mech"title="Permalink to this headline">¶</a></h1>
<p>Let us create a functioning giant mech in Evennia. Everyone likes a giant mech, right? Start in-game as a character with build privileges (or the superuser).</p>
<p>This makes it so that everyone can control the mech. More mechs to the people! (Note that whereas Evennia’s default commands may look vaguely MUX-like, you can change the syntax to look like whatever interface style you prefer.)</p>
<p>Before we continue, let’s make a brief detour. Evennia is very flexible about its objects and even more flexible about using and adding commands to those objects. Here are some ground rules well worth remembering for the remainder of this article:</p>
<li><p>The <aclass="reference internal"href="../Components/Accounts.html"><spanclass="doc std std-doc">Account</span></a> represents the real person logging in and has no game-world existence.</p></li>
<li><p>Any <aclass="reference internal"href="../Components/Objects.html"><spanclass="doc std std-doc">Object</span></a> can be puppeted by an Account (with proper permissions).</p></li>
<li><p><spanclass="xref myst">Characters</span>, <spanclass="xref myst">Rooms</span>, and <spanclass="xref myst">Exits</span> are just children of normal Objects.</p></li>
<li><p>Also Accounts can store commands on themselves. Account commands are always available unless commands on a puppeted Object explicitly override them.</p></li>
<p>In Evennia, using the <codeclass="docutils literal notranslate"><spanclass="pre">ic</span></code> command will allow you to puppet a given Object (assuming you have puppet-access to do so). As mentioned above, the bog-standard Character class is in fact like any Object: it is auto-puppeted when logging in and just has a command set on it containing the normal in-game commands, like look, inventory, get and so on.</p>
<div><p>Where did that <codeclass="docutils literal notranslate"><spanclass="pre">ic</span></code> command come from, if the mech had no commands on it? The
answer is that it came from the <codeclass="docutils literal notranslate"><spanclass="pre">Account</span></code>’s command set. This is important. Without the Account being the one with the <codeclass="docutils literal notranslate"><spanclass="pre">ic</span></code> command, we would not have been able to get back out of our mech again.</p>
<p>Let us make the mech a little more interesting. In our favorite text editor, we will create some new
mech-suitable commands. In Evennia, commands are defined as Python classes.</p>
<divclass="highlight-python notranslate"><divclass="highlight"><pre><span></span><spanclass="c1"># in a new file mygame/commands/mechcommands.py</span>
<spanclass="sa">f</span><spanclass="s2">"BOOM! The mech fires its gun at </span><spanclass="si">{</span><spanclass="n">target</span><spanclass="o">.</span><spanclass="n">key</span><spanclass="si">}</span><spanclass="s2">"</span>
<p>This is saved as a normal Python module (let’s call it <codeclass="docutils literal notranslate"><spanclass="pre">mechcommands.py</span></code>), in a place Evennia looks for such modules (<codeclass="docutils literal notranslate"><spanclass="pre">mygame/commands/</span></code>). This command will trigger when the player gives the command “shoot”, “fire,” or even “fire!” with an exclamation mark. The mech can shoot in the air or at a target if you give one. In a real game the gun would probably be given a chance to hit and give
<p>We also make a second command for launching missiles (<codeclass="docutils literal notranslate"><spanclass="pre">CmdLaunch</span></code>). To save space we won’t describe it here; it looks the same except it returns a text about the missiles being fired and has different <codeclass="docutils literal notranslate"><spanclass="pre">key</span></code> and <codeclass="docutils literal notranslate"><spanclass="pre">aliases</span></code>. We leave that up to you to create as an exercise. You could have it print <codeclass="docutils literal notranslate"><spanclass="pre">"WOOSH!</span><spanclass="pre">The</span><spanclass="pre">mech</span><spanclass="pre">launches</span><spanclass="pre">missiles</span><spanclass="pre">against</span><spanclass="pre"><target>!</span></code>, for example.</p>
<p>Now we shove our commands into a command set. A <aclass="reference internal"href="../Components/Command-Sets.html"><spanclass="doc std std-doc">Command Set</span></a> (CmdSet) is a container holding any number of commands. The command set is what we will store on the mech.</p>
<divclass="highlight-python notranslate"><divclass="highlight"><pre><span></span><spanclass="c1"># in the same file mygame/commands/mechcommands.py</span>
<p>This simply groups all the commands we want. We add our new shoot/launch commands. Let’s head back into the game. For testing we will manually attach our new CmdSet to the mech.</p>
<p>This is a little Python snippet that searches for the mech in our current location and attaches our new MechCmdSet to it. What we add is actually the Python path to our cmdset class. Evennia will import and initialize it behind the scenes.</p>
<p>There we go, one functioning mech. Try your own <codeclass="docutils literal notranslate"><spanclass="pre">launch</span></code> command and see that it works too. We can not only walk around as the mech — since the CharacterCmdSet is included in our MechCmdSet, the mech can also do everything a Character could do, like look around, pick up stuff, and have an inventory. We could now shoot the gun at a target or try the missile launch command. Once you have your own mech, what else do you need?</p>
server. Now we want to make the mech an actual object “type” so we can create mechs without those extra steps. For this we need to create a new Typeclass.</p>
<p>A <aclass="reference internal"href="../Components/Typeclasses.html"><spanclass="doc std std-doc">Typeclass</span></a> is a near-normal Python class that stores its existence to the database
behind the scenes. A Typeclass is created in a normal Python source file:</p>
<divclass="highlight-python notranslate"><divclass="highlight"><pre><span></span><spanclass="c1"># in the new file mygame/typeclasses/mech.py</span>
<spanclass="bp">self</span><spanclass="o">.</span><spanclass="n">db</span><spanclass="o">.</span><spanclass="n">desc</span><spanclass="o">=</span><spanclass="s2">"This is a huge mech. It has missiles and stuff."</span>
<p>For convenience we include the full contents of the default <codeclass="docutils literal notranslate"><spanclass="pre">CharacterCmdSet</span></code> in there. This will make a Character’s normal commands available to the mech. We also add the mech-commands from before, making sure they are stored persistently in the database. The locks specify that anyone can puppet the meck and no-one can “call” the mech’s Commands from ‘outside’ it - you have to puppet it to be able to shoot.</p>
<p>That’s it. When Objects of this type are created, they will always start out with the mech’s command set and the correct lock. We set a default description, but you would probably change this with <codeclass="docutils literal notranslate"><spanclass="pre">desc</span></code> to individualize your mechs as you build them.</p>
<p>Back in the game, just exit the old mech (<codeclass="docutils literal notranslate"><spanclass="pre">@ic</span></code> back to your old character) then do</p>
have to give the full path in our game dir <codeclass="docutils literal notranslate"><spanclass="pre">typeclasses.mech.Mech</span></code> because Evennia knows to look in the <codeclass="docutils literal notranslate"><spanclass="pre">typeclasses</span></code> folder already). A shining new mech will appear in the room! Just use</p>
Character (since any Object can move inside another). In that case the “insides” of the mech Object could be the “cockpit”. The cockpit would have the <codeclass="docutils literal notranslate"><spanclass="pre">MechCommandSet</span></code> stored on itself and all the shooting goodness would be made available to you only when you enter it.</p>
<p>To expand on this you could add more commands to the mech and remove others. Maybe the mech shouldn’t work just like a Character after all.</p>
<p>Maybe it makes loud noises every time it passes from room to room. Maybe it cannot pick up things without crushing them. Maybe it needs fuel, ammo and repairs. Maybe you’ll lock it down so it can only be puppeted by emo teenagers.</p>
