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<h3><a href="../../../index.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">5. Handling Equipment</a><ul>
<li><a class="reference internal" href="#equipmenthandler-that-saves">5.1. EquipmentHandler that saves</a></li>
<li><a class="reference internal" href="#connecting-the-equipmenthandler">5.2. Connecting the EquipmentHandler</a></li>
<li><a class="reference internal" href="#expanding-the-equipmenthandler">5.3. Expanding the Equipmenthandler</a></li>
<li><a class="reference internal" href="#validate-slot-usage">5.4. <code class="docutils literal notranslate"><span class="pre">.validate_slot_usage</span></code></a><ul>
<li><a class="reference internal" href="#max-slots">5.4.1. <code class="docutils literal notranslate"><span class="pre">.max_slots</span></code></a></li>
<li><a class="reference internal" href="#count-slots">5.4.2. <code class="docutils literal notranslate"><span class="pre">.count_slots</span></code></a></li>
<li><a class="reference internal" href="#validating-slots">5.4.3. Validating slots</a></li>
</ul>
</li>
<li><a class="reference internal" href="#add-and-remove">5.5. <code class="docutils literal notranslate"><span class="pre">.add</span></code> and <code class="docutils literal notranslate"><span class="pre">.remove</span></code></a></li>
<li><a class="reference internal" href="#moving-things-around">5.6. Moving things around</a></li>
<li><a class="reference internal" href="#get-everything">5.7. Get everything</a></li>
<li><a class="reference internal" href="#weapon-and-armor">5.8. Weapon and armor</a><ul>
<li><a class="reference internal" href="#fixing-the-character-class">5.8.1. Fixing the Character class</a></li>
</ul>
</li>
<li><a class="reference internal" href="#extra-credits">5.9. Extra credits</a></li>
<li><a class="reference internal" href="#unit-testing">5.10. Unit Testing</a></li>
<li><a class="reference internal" href="#summary">5.11. Summary</a></li>
</ul>
</li>
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<section class="tex2jax_ignore mathjax_ignore" id="handling-equipment">
<h1><span class="section-number">5. </span>Handling Equipment<a class="headerlink" href="#handling-equipment" title="Permalink to this headline"></a></h1>
<p>In <em>Knave</em>, you have a certain number of inventory “slots”. The amount of slots is given by <code class="docutils literal notranslate"><span class="pre">CON</span> <span class="pre">+</span> <span class="pre">10</span></code>. All items (except coins) have a <code class="docutils literal notranslate"><span class="pre">size</span></code>, indicating how many slots it uses. You can’t carry more items than you have slot-space for. Also items wielded or worn count towards the slots.</p>
<p>We still need to track what the character is using however: What weapon they have readied affects the damage they can do. The shield, helmet and armor they use affects their defense.</p>
<p>We have already set up the possible ‘wear/wield locations’ when we defined our Objects
<a class="reference internal" href="Beginner-Tutorial-Objects.html"><span class="doc std std-doc">in the previous lesson</span></a>. This is what we have in <code class="docutils literal notranslate"><span class="pre">enums.py</span></code>:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/enums.py</span>
<span class="c1"># ...</span>
<span class="k">class</span> <span class="nc">WieldLocation</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="n">BACKPACK</span> <span class="o">=</span> <span class="s2">&quot;backpack&quot;</span>
<span class="n">WEAPON_HAND</span> <span class="o">=</span> <span class="s2">&quot;weapon_hand&quot;</span>
<span class="n">SHIELD_HAND</span> <span class="o">=</span> <span class="s2">&quot;shield_hand&quot;</span>
<span class="n">TWO_HANDS</span> <span class="o">=</span> <span class="s2">&quot;two_handed_weapons&quot;</span>
<span class="n">BODY</span> <span class="o">=</span> <span class="s2">&quot;body&quot;</span> <span class="c1"># armor</span>
<span class="n">HEAD</span> <span class="o">=</span> <span class="s2">&quot;head&quot;</span> <span class="c1"># helmets</span>
</pre></div>
</div>
<p>Basically, all the weapon/armor locations are exclusive - you can only have one item in each (or none). The BACKPACK is special - it contains any number of items (up to the maximum slot usage).</p>
<section id="equipmenthandler-that-saves">
<h2><span class="section-number">5.1. </span>EquipmentHandler that saves<a class="headerlink" href="#equipmenthandler-that-saves" title="Permalink to this headline"></a></h2>
<blockquote>
<div><p>Create a new module <code class="docutils literal notranslate"><span class="pre">mygame/evadventure/equipment.py</span></code>.</p>
</div></blockquote>
<aside class="sidebar">
<p>If you want to understand more about behind how Evennia uses handlers, there is a
<a class="reference internal" href="../../Tutorial-Persistent-Handler.html"><span class="doc std std-doc">dedicated tutorial</span></a> talking about the principle.</p>
</aside>
<p>In default Evennia, everything you pick up will end up “inside” your character object (that is, have you as its <code class="docutils literal notranslate"><span class="pre">.location</span></code>). This is called your <em>inventory</em> and has no limit. We will keep ‘moving items into us’ when we pick them up, but we will add more functionality using an <em>Equipment handler</em>.</p>
<p>A handler is (for our purposes) an object that sits “on” another entity, containing functionality for doing one specific thing (managing equipment, in our case).</p>
<p>This is the start of our handler:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># in mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="n">save_attribute</span> <span class="o">=</span> <span class="s2">&quot;inventory_slots&quot;</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span>
<span class="c1"># here obj is the character we store the handler on </span>
<span class="bp">self</span><span class="o">.</span><span class="n">obj</span> <span class="o">=</span> <span class="n">obj</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_load</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">_load</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Load our data from an Attribute on `self.obj`&quot;&quot;&quot;</span>
<span class="bp">self</span><span class="o">.</span><span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">obj</span><span class="o">.</span><span class="n">attributes</span><span class="o">.</span><span class="n">get</span><span class="p">(</span>
<span class="bp">self</span><span class="o">.</span><span class="n">save_attribute</span><span class="p">,</span>
<span class="n">category</span><span class="o">=</span><span class="s2">&quot;inventory&quot;</span><span class="p">,</span>
<span class="n">default</span><span class="o">=</span><span class="p">{</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">:</span> <span class="kc">None</span><span class="p">,</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">:</span> <span class="kc">None</span><span class="p">,</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">:</span> <span class="kc">None</span><span class="p">,</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">BODY</span><span class="p">:</span> <span class="kc">None</span><span class="p">,</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">HEAD</span><span class="p">:</span> <span class="kc">None</span><span class="p">,</span>
<span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">:</span> <span class="p">[]</span>
<span class="p">}</span>
<span class="p">)</span>
<span class="k">def</span> <span class="nf">_save</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Save our data back to the same Attribute&quot;&quot;&quot;</span>
<span class="bp">self</span><span class="o">.</span><span class="n">obj</span><span class="o">.</span><span class="n">attributes</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">save_attribute</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span><span class="p">,</span> <span class="n">category</span><span class="o">=</span><span class="s2">&quot;inventory&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>This is a compact and functional little handler. Before analyzing how it works, this is how
we will add it to the Character:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/characters.py</span>
<span class="c1"># ... </span>
<span class="kn">from</span> <span class="nn">evennia.utils.utils</span> <span class="kn">import</span> <span class="n">lazy_property</span>
<span class="kn">from</span> <span class="nn">.equipment</span> <span class="kn">import</span> <span class="n">EquipmentHandler</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EvAdventureCharacter</span><span class="p">(</span><span class="n">LivingMixin</span><span class="p">,</span> <span class="n">DefaultCharacter</span><span class="p">):</span>
<span class="c1"># ... </span>
<span class="nd">@lazy_property</span>
<span class="k">def</span> <span class="nf">equipment</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="n">EquipmentHandler</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
</pre></div>
</div>
<p>After reloading the server, the equipment-handler will now be accessible on character-instances as</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>character.equipment
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">&#64;lazy_property</span></code> works such that it will not load the handler until someone actually tries to fetch it with <code class="docutils literal notranslate"><span class="pre">character.equipment</span></code>. When that happens, we start up the handler and feed it <code class="docutils literal notranslate"><span class="pre">self</span></code> (the <code class="docutils literal notranslate"><span class="pre">Character</span></code> instance itself). This is what enters <code class="docutils literal notranslate"><span class="pre">__init__</span></code> as <code class="docutils literal notranslate"><span class="pre">.obj</span></code> in the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> code above.</p>
<p>So we now have a handler on the character, and the handler has a back-reference to the character it sits on.</p>
<p>Since the handler itself is just a regular Python object, we need to use the <code class="docutils literal notranslate"><span class="pre">Character</span></code> to store
our data - our <em>Knave</em> “slots”. We must save them to the database, because we want the server to remember them even after reloading.</p>
<p>Using <code class="docutils literal notranslate"><span class="pre">self.obj.attributes.add()</span></code> and <code class="docutils literal notranslate"><span class="pre">.get()</span></code> we save the data to the Character in a specially named <a class="reference internal" href="../../../Components/Attributes.html"><span class="doc std std-doc">Attribute</span></a>. Since we use a <code class="docutils literal notranslate"><span class="pre">category</span></code>, we are unlikely to collide with
other Attributes.</p>
<p>Our storage structure is a <code class="docutils literal notranslate"><span class="pre">dict</span></code> with keys after our available <code class="docutils literal notranslate"><span class="pre">WieldLocation</span></code> enums. Each can only have one item except <code class="docutils literal notranslate"><span class="pre">WieldLocation.BACKPACK</span></code>, which is a list.</p>
</section>
<section id="connecting-the-equipmenthandler">
<h2><span class="section-number">5.2. </span>Connecting the EquipmentHandler<a class="headerlink" href="#connecting-the-equipmenthandler" title="Permalink to this headline"></a></h2>
<p>Whenever an object leaves from one location to the next, Evennia will call a set of <em>hooks</em> (methods) on the object that moves, on the source-location and on its destination. This is the same for all moving things - whether it’s a character moving between rooms or an item being dropping from your hand to the ground.</p>
<p>We need to tie our new <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> into this system. By reading the doc page on <a class="reference internal" href="../../../Components/Objects.html"><span class="doc std std-doc">Objects</span></a>, or looking at the <a class="reference internal" href="../../../api/evennia.objects.objects.html#evennia.objects.objects.DefaultObject.move_to" title="evennia.objects.objects.DefaultObject.move_to"><span class="xref myst py py-meth">DefaultObject.move_to</span></a> docstring, we’ll find out what hooks Evennia will call. Here <code class="docutils literal notranslate"><span class="pre">self</span></code> is the object being moved from <code class="docutils literal notranslate"><span class="pre">source_location</span></code> to <code class="docutils literal notranslate"><span class="pre">destination</span></code>:</p>
<ol class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">self.at_pre_move(destination)</span></code> (abort if return False)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">source_location.at_pre_object_leave(self,</span> <span class="pre">destination)</span></code> (abort if return False)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">destination.at_pre_object_receive(self,</span> <span class="pre">source_location)</span></code> (abort if return False)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">source_location.at_object_leave(self,</span> <span class="pre">destination)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">self.announce_move_from(destination)</span></code></p></li>
<li><p>(move happens here)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">self.announce_move_to(source_location)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">destination.at_object_receive(self,</span> <span class="pre">source_location)</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">self.at_post_move(source_location)</span></code></p></li>
</ol>
<p>All of these hooks can be overridden to customize movement behavior. In this case we are interested in controlling how items ‘enter’ and ‘leave’ our character - being ‘inside’ the character is the same as them ‘carrying’ it. We have three good hook-candidates to use for this.</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">.at_pre_object_receive</span></code> - used to check if you can actually pick something up, or if your equipment-store is full.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">.at_object_receive</span></code> - used to add the item to the equipmenthandler</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">.at_object_leave</span></code> - used to remove the item from the equipmenthandler</p></li>
</ul>
<p>You could also picture using <code class="docutils literal notranslate"><span class="pre">.at_pre_object_leave</span></code> to restrict dropping (cursed?) items, but
we will skip that for this tutorial.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/character.py </span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EvAdventureCharacter</span><span class="p">(</span><span class="n">LivingMixin</span><span class="p">,</span> <span class="n">DefaultCharacter</span><span class="p">):</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">at_pre_object_receive</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">moved_object</span><span class="p">,</span> <span class="n">source_location</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Called by Evennia before object arrives &#39;in&#39; this character (that is,</span>
<span class="sd"> if they pick up something). If it returns False, move is aborted.</span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">validate_slot_usage</span><span class="p">(</span><span class="n">moved_object</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">at_object_receive</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">moved_object</span><span class="p">,</span> <span class="n">source_location</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot; </span>
<span class="sd"> Called by Evennia when an object arrives &#39;in&#39; the character.</span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="bp">self</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">moved_object</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">at_object_leave</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">moved_object</span><span class="p">,</span> <span class="n">destination</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot; </span>
<span class="sd"> Called by Evennia when object leaves the Character. </span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="bp">self</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">moved_object</span><span class="p">)</span>
</pre></div>
</div>
<p>Above we have assumed the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> (<code class="docutils literal notranslate"><span class="pre">.equipment</span></code>) has methods <code class="docutils literal notranslate"><span class="pre">.validate_slot_usage</span></code>, <code class="docutils literal notranslate"><span class="pre">.add</span></code> and <code class="docutils literal notranslate"><span class="pre">.remove</span></code>. But we haven’t actually added them yet - we just put some reasonable names! Before we can use this, we need to go actually adding those methods.</p>
<p>When you do things like <code class="docutils literal notranslate"><span class="pre">create/drop</span> <span class="pre">monster:NPC</span></code>, the npc will briefly be in your inventory before being dropped on the ground. Since an NPC is not a valid thing to equip, the EquipmentHandler will complain with an <code class="docutils literal notranslate"><span class="pre">EquipmentError</span></code> (we define this see below). So we need to</p>
</section>
<section id="expanding-the-equipmenthandler">
<h2><span class="section-number">5.3. </span>Expanding the Equipmenthandler<a class="headerlink" href="#expanding-the-equipmenthandler" title="Permalink to this headline"></a></h2>
</section>
<section id="validate-slot-usage">
<h2><span class="section-number">5.4. </span><code class="docutils literal notranslate"><span class="pre">.validate_slot_usage</span></code><a class="headerlink" href="#validate-slot-usage" title="Permalink to this headline"></a></h2>
<p>Let’s start with implementing the first method we came up with above, <code class="docutils literal notranslate"><span class="pre">validate_slot_usage</span></code>:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span><span class="p">,</span> <span class="n">Ability</span>
<span class="k">class</span> <span class="nc">EquipmentError</span><span class="p">(</span><span class="ne">TypeError</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;All types of equipment-errors&quot;&quot;&quot;</span>
<span class="k">pass</span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="c1"># ... </span>
<span class="nd">@property</span>
<span class="k">def</span> <span class="nf">max_slots</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Max amount of slots, based on CON defense (CON + 10)&quot;&quot;&quot;</span>
<span class="k">return</span> <span class="nb">getattr</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">obj</span><span class="p">,</span> <span class="n">Ability</span><span class="o">.</span><span class="n">CON</span><span class="o">.</span><span class="n">value</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="mi">10</span>
<span class="k">def</span> <span class="nf">count_slots</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Count current slot usage&quot;&quot;&quot;</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="n">wield_usage</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slotobj</span><span class="p">,</span> <span class="s2">&quot;size&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="ow">or</span> <span class="mi">0</span>
<span class="k">for</span> <span class="n">slot</span><span class="p">,</span> <span class="n">slotobj</span> <span class="ow">in</span> <span class="n">slots</span><span class="o">.</span><span class="n">items</span><span class="p">()</span>
<span class="k">if</span> <span class="n">slot</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span>
<span class="p">)</span>
<span class="n">backpack_usage</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slotobj</span><span class="p">,</span> <span class="s2">&quot;size&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span> <span class="ow">or</span> <span class="mi">0</span> <span class="k">for</span> <span class="n">slotobj</span> <span class="ow">in</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">]</span>
<span class="p">)</span>
<span class="k">return</span> <span class="n">wield_usage</span> <span class="o">+</span> <span class="n">backpack_usage</span>
<span class="k">def</span> <span class="nf">validate_slot_usage</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> Check if obj can fit in equipment, based on its size.</span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">inherits_from</span><span class="p">(</span><span class="n">obj</span><span class="p">,</span> <span class="n">EvAdventureObject</span><span class="p">):</span>
<span class="c1"># in case we mix with non-evadventure objects</span>
<span class="k">raise</span> <span class="n">EquipmentError</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;</span><span class="si">{</span><span class="n">obj</span><span class="o">.</span><span class="n">key</span><span class="si">}</span><span class="s2"> is not something that can be equipped.&quot;</span><span class="p">)</span>
<span class="n">size</span> <span class="o">=</span> <span class="n">obj</span><span class="o">.</span><span class="n">size</span>
<span class="n">max_slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">max_slots</span>
<span class="n">current_slot_usage</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">count_slots</span><span class="p">()</span>
<span class="k">return</span> <span class="n">current_slot_usage</span> <span class="o">+</span> <span class="n">size</span> <span class="o">&lt;=</span> <span class="n">max_slots</span>
</pre></div>
</div>
<aside class="sidebar">
<p>The <code class="docutils literal notranslate"><span class="pre">&#64;property</span></code> decorator turns a method into a property so you don’t need to ‘call’ it.
That is, you can access <code class="docutils literal notranslate"><span class="pre">.max_slots</span></code> instead of <code class="docutils literal notranslate"><span class="pre">.max_slots()</span></code>. In this case, it’s just a
little less to type.</p>
</aside>
<p>We add two helpers - the <code class="docutils literal notranslate"><span class="pre">max_slots</span></code> <em>property</em> and <code class="docutils literal notranslate"><span class="pre">count_slots</span></code>, a method that calculate the current slots being in use. Let’s figure out how they work.</p>
<section id="max-slots">
<h3><span class="section-number">5.4.1. </span><code class="docutils literal notranslate"><span class="pre">.max_slots</span></code><a class="headerlink" href="#max-slots" title="Permalink to this headline"></a></h3>
<p>For <code class="docutils literal notranslate"><span class="pre">max_slots</span></code>, remember that <code class="docutils literal notranslate"><span class="pre">.obj</span></code> on the handler is a back-reference to the <code class="docutils literal notranslate"><span class="pre">EvAdventureCharacter</span></code> we put this handler on. <code class="docutils literal notranslate"><span class="pre">getattr</span></code> is a Python method for retrieving a named property on an object. The <code class="docutils literal notranslate"><span class="pre">Enum</span></code> <code class="docutils literal notranslate"><span class="pre">Ability.CON.value</span></code> is the string <code class="docutils literal notranslate"><span class="pre">Constitution</span></code> (check out the <a class="reference internal" href="Beginner-Tutorial-Utilities.html"><span class="doc std std-doc">first Utility and Enums tutorial</span></a> if you don’t recall).</p>
<p>So to be clear,</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="nb">getattr</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">obj</span><span class="p">,</span> <span class="n">Ability</span><span class="o">.</span><span class="n">CON</span><span class="o">.</span><span class="n">value</span><span class="p">)</span> <span class="o">+</span> <span class="mi">10</span>
</pre></div>
</div>
<p>is the same as writing</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="nb">getattr</span><span class="p">(</span><span class="n">your_character</span><span class="p">,</span> <span class="s2">&quot;Constitution&quot;</span><span class="p">)</span> <span class="o">+</span> <span class="mi">10</span>
</pre></div>
</div>
<p>which is the same as doing something like this:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">your_character</span><span class="o">.</span><span class="n">Constitution</span> <span class="o">+</span> <span class="mi">10</span>
</pre></div>
</div>
<p>In our code we write <code class="docutils literal notranslate"><span class="pre">getattr(self.obj,</span> <span class="pre">Ability.CON.value,</span> <span class="pre">1)</span></code> - that extra <code class="docutils literal notranslate"><span class="pre">1</span></code> means that if there should happen to <em>not</em> be a property “Constitution” on <code class="docutils literal notranslate"><span class="pre">self.obj</span></code>, we should not error out but just return 1.</p>
</section>
<section id="count-slots">
<h3><span class="section-number">5.4.2. </span><code class="docutils literal notranslate"><span class="pre">.count_slots</span></code><a class="headerlink" href="#count-slots" title="Permalink to this headline"></a></h3>
<p>In this helper we use two Python tools - the <code class="docutils literal notranslate"><span class="pre">sum()</span></code> function and a <a class="reference external" href="https://www.w3schools.com/python/python_lists_comprehension.asp">list comprehension</a>. The former simply adds the values of any iterable together. The latter is a more efficient way to create a list:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>new_list = [item for item in some_iterable if condition]
all_above_5 = [num for num in range(10) if num &gt; 5] # [6, 7, 8, 9]
all_below_5 = [num for num in range(10) if num &lt; 5] # [0, 1, 2, 3, 4]
</pre></div>
</div>
<p>To make it easier to understand, try reading the last line above as “for every number in the range 0-9, pick all with a value below 5 and make a list of them”. You can also embed such comprehensions directly in a function call like <code class="docutils literal notranslate"><span class="pre">sum()</span></code> without using <code class="docutils literal notranslate"><span class="pre">[]</span></code> around it.</p>
<p>In <code class="docutils literal notranslate"><span class="pre">count_slots</span></code> we have this code:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">wield_usage</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slotobj</span><span class="p">,</span> <span class="s2">&quot;size&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="k">for</span> <span class="n">slot</span><span class="p">,</span> <span class="n">slotobj</span> <span class="ow">in</span> <span class="n">slots</span><span class="o">.</span><span class="n">items</span><span class="p">()</span>
<span class="k">if</span> <span class="n">slot</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span>
<span class="p">)</span>
</pre></div>
</div>
<p>We should be able to follow all except <code class="docutils literal notranslate"><span class="pre">slots.items()</span></code>. Since <code class="docutils literal notranslate"><span class="pre">slots</span></code> is a <code class="docutils literal notranslate"><span class="pre">dict</span></code>, we can use <code class="docutils literal notranslate"><span class="pre">.items()</span></code> to get a sequence of <code class="docutils literal notranslate"><span class="pre">(key,</span> <span class="pre">value)</span></code> pairs. We store these in <code class="docutils literal notranslate"><span class="pre">slot</span></code> and <code class="docutils literal notranslate"><span class="pre">slotobj</span></code>. So the above can be understood as “for every <code class="docutils literal notranslate"><span class="pre">slot</span></code> and <code class="docutils literal notranslate"><span class="pre">slotobj</span></code>-pair in <code class="docutils literal notranslate"><span class="pre">slots</span></code>, check which slot location it is. If it is <em>not</em> in the backpack, get its size and add it to the list. Sum over all these
sizes”.</p>
<p>A less compact but maybe more readonable way to write this would be:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">backpack_item_sizes</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">for</span> <span class="n">slot</span><span class="p">,</span> <span class="n">slotobj</span> <span class="ow">in</span> <span class="n">slots</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="k">if</span> <span class="n">slot</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">:</span>
<span class="n">size</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">slotobj</span><span class="p">,</span> <span class="s2">&quot;size&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="n">backpack_item_sizes</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">size</span><span class="p">)</span>
<span class="n">wield_usage</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">backpack_item_sizes</span><span class="p">)</span>
</pre></div>
</div>
<p>The same is done for the items actually in the BACKPACK slot. The total sizes are added
together.</p>
</section>
<section id="validating-slots">
<h3><span class="section-number">5.4.3. </span>Validating slots<a class="headerlink" href="#validating-slots" title="Permalink to this headline"></a></h3>
<p>With these helpers in place, <code class="docutils literal notranslate"><span class="pre">validate_slot_usage</span></code> now becomes simple. We use <code class="docutils literal notranslate"><span class="pre">max_slots</span></code> to see how much we can carry. We then get how many slots we are already using (with <code class="docutils literal notranslate"><span class="pre">count_slots</span></code>) and see if our new <code class="docutils literal notranslate"><span class="pre">obj</span></code>’s size would be too much for us.</p>
</section>
</section>
<section id="add-and-remove">
<h2><span class="section-number">5.5. </span><code class="docutils literal notranslate"><span class="pre">.add</span></code> and <code class="docutils literal notranslate"><span class="pre">.remove</span></code><a class="headerlink" href="#add-and-remove" title="Permalink to this headline"></a></h2>
<p>We will make it so <code class="docutils literal notranslate"><span class="pre">.add</span></code> puts something in the <code class="docutils literal notranslate"><span class="pre">BACKPACK</span></code> location and <code class="docutils literal notranslate"><span class="pre">remove</span></code> drops it, wherever it is (even if it was in your hands).</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span><span class="p">,</span> <span class="n">Ability</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">add</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> Put something in the backpack.</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">validate_slot_usage</span><span class="p">(</span><span class="n">obj</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">obj</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_save</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">remove</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj_or_slot</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> Remove specific object or objects from a slot.</span>
<span class="sd"> Returns a list of 0, 1 or more objects removed from inventory.</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="n">ret</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">obj_or_slot</span><span class="p">,</span> <span class="n">WieldLocation</span><span class="p">):</span>
<span class="c1"># a slot; if this fails, obj_or_slot must be obj</span>
<span class="k">if</span> <span class="n">obj_or_slot</span> <span class="ow">is</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">:</span>
<span class="c1"># empty entire backpack</span>
<span class="n">ret</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">obj_or_slot</span><span class="p">])</span>
<span class="n">slots</span><span class="p">[</span><span class="n">obj_or_slot</span><span class="p">]</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">ret</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">obj_or_slot</span><span class="p">])</span>
<span class="n">slots</span><span class="p">[</span><span class="n">obj_or_slot</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">elif</span> <span class="n">obj_or_slot</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span><span class="o">.</span><span class="n">values</span><span class="p">():</span>
<span class="c1"># obj in use/wear slot</span>
<span class="k">for</span> <span class="n">slot</span><span class="p">,</span> <span class="n">objslot</span> <span class="ow">in</span> <span class="n">slots</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="k">if</span> <span class="n">objslot</span> <span class="ow">is</span> <span class="n">obj_or_slot</span><span class="p">:</span>
<span class="n">slots</span><span class="p">[</span><span class="n">slot</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>
<span class="n">ret</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">objslot</span><span class="p">)</span>
<span class="k">elif</span> <span class="n">obj_or_slot</span> <span class="ow">in</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">]:</span> <span class="c1"># obj in backpack slot</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">]</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">obj_or_slot</span><span class="p">)</span>
<span class="n">ret</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">obj_or_slot</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">ValueError</span><span class="p">:</span>
<span class="k">pass</span>
<span class="k">if</span> <span class="n">ret</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_save</span><span class="p">()</span>
<span class="k">return</span> <span class="n">ret</span>
</pre></div>
</div>
<p>In <code class="docutils literal notranslate"><span class="pre">.add</span></code>, we make use of <code class="docutils literal notranslate"><span class="pre">validate_slot_usage</span></code> to
double-check we can actually fit the thing, then we add the item to the backpack.</p>
<p>In <code class="docutils literal notranslate"><span class="pre">.remove</span></code>, we allow emptying both by <code class="docutils literal notranslate"><span class="pre">WieldLocation</span></code> or by explicitly saying which object to remove. Note that the first <code class="docutils literal notranslate"><span class="pre">if</span></code> statement checks if <code class="docutils literal notranslate"><span class="pre">obj_or_slot</span></code> is a slot. So if that fails then code in the other <code class="docutils literal notranslate"><span class="pre">elif</span></code> can safely assume that it must instead be an object!</p>
<p>Any removed objects are returned. If we gave <code class="docutils literal notranslate"><span class="pre">BACKPACK</span></code> as the slot, we empty the backpack and return all items inside it.</p>
<p>Whenever we change the equipment loadout we must make sure to <code class="docutils literal notranslate"><span class="pre">._save()</span></code> the result, or it will be lost after a server reload.</p>
</section>
<section id="moving-things-around">
<h2><span class="section-number">5.6. </span>Moving things around<a class="headerlink" href="#moving-things-around" title="Permalink to this headline"></a></h2>
<p>With the help of <code class="docutils literal notranslate"><span class="pre">.remove()</span></code> and <code class="docutils literal notranslate"><span class="pre">.add()</span></code> we can get things in and out of the <code class="docutils literal notranslate"><span class="pre">BACKPACK</span></code> equipment location. We also need to grab stuff from the backpack and wield or wear it. We add a <code class="docutils literal notranslate"><span class="pre">.move</span></code> method on the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> to do this:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span><span class="p">,</span> <span class="n">Ability</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">move</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obj</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;Move object from backpack to its intended `inventory_use_slot`.&quot;&quot;&quot;</span>
<span class="c1"># make sure to remove from equipment/backpack first, to avoid double-adding</span>
<span class="bp">self</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="n">obj</span><span class="p">)</span>
<span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">validate_slot_usage</span><span class="p">(</span><span class="n">obj</span><span class="p">):</span>
<span class="k">return</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="n">use_slot</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">obj</span><span class="p">,</span> <span class="s2">&quot;inventory_use_slot&quot;</span><span class="p">,</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">)</span>
<span class="n">to_backpack</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">if</span> <span class="n">use_slot</span> <span class="ow">is</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">:</span>
<span class="c1"># two-handed weapons can&#39;t co-exist with weapon/shield-hand used items</span>
<span class="n">to_backpack</span> <span class="o">=</span> <span class="p">[</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">],</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">]]</span>
<span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">]</span> <span class="o">=</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>
<span class="n">slots</span><span class="p">[</span><span class="n">use_slot</span><span class="p">]</span> <span class="o">=</span> <span class="n">obj</span>
<span class="k">elif</span> <span class="n">use_slot</span> <span class="ow">in</span> <span class="p">(</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">,</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">):</span>
<span class="c1"># can&#39;t keep a two-handed weapon if adding a one-handed weapon or shield</span>
<span class="n">to_backpack</span> <span class="o">=</span> <span class="p">[</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">]]</span>
<span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span>
<span class="n">slots</span><span class="p">[</span><span class="n">use_slot</span><span class="p">]</span> <span class="o">=</span> <span class="n">obj</span>
<span class="k">elif</span> <span class="n">use_slot</span> <span class="ow">is</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">:</span>
<span class="c1"># it belongs in backpack, so goes back to it</span>
<span class="n">to_backpack</span> <span class="o">=</span> <span class="p">[</span><span class="n">obj</span><span class="p">]</span>
<span class="k">else</span><span class="p">:</span>
<span class="c1"># for others (body, head), just replace whatever&#39;s there</span>
<span class="n">replaced</span> <span class="o">=</span> <span class="p">[</span><span class="n">obj</span><span class="p">]</span>
<span class="n">slots</span><span class="p">[</span><span class="n">use_slot</span><span class="p">]</span> <span class="o">=</span> <span class="n">obj</span>
<span class="k">for</span> <span class="n">to_backpack_obj</span> <span class="ow">in</span> <span class="n">to_backpack</span><span class="p">:</span>
<span class="c1"># put stuff in backpack</span>
<span class="n">slots</span><span class="p">[</span><span class="n">use_slot</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">to_backpack_obj</span><span class="p">)</span>
<span class="c1"># store new state</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_save</span><span class="p">()</span>
</pre></div>
</div>
<p>Here we remember that every <code class="docutils literal notranslate"><span class="pre">EvAdventureObject</span></code> has an <code class="docutils literal notranslate"><span class="pre">inventory_use_slot</span></code> property that tells us where it goes. So we just need to move the object to that slot, replacing whatever is in that place from before. Anything we replace goes back to the backpack.</p>
</section>
<section id="get-everything">
<h2><span class="section-number">5.7. </span>Get everything<a class="headerlink" href="#get-everything" title="Permalink to this headline"></a></h2>
<p>In order to visualize our inventory, we need some method to get everything we are carrying.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span><span class="p">,</span> <span class="n">Ability</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">all</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd"> Get all objects in inventory, regardless of location.</span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="n">lst</span> <span class="o">=</span> <span class="p">[</span>
<span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">],</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">),</span>
<span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">],</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">),</span>
<span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">],</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">),</span>
<span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BODY</span><span class="p">],</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BODY</span><span class="p">),</span>
<span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">HEAD</span><span class="p">],</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">HEAD</span><span class="p">),</span>
<span class="p">]</span> <span class="o">+</span> <span class="p">[(</span><span class="n">item</span><span class="p">,</span> <span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">)</span> <span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">]]</span>
<span class="k">return</span> <span class="n">lst</span>
</pre></div>
</div>
<p>Here we get all the equipment locations and add their contents together into a list of tuples
<code class="docutils literal notranslate"><span class="pre">[(item,</span> <span class="pre">WieldLocation),</span> <span class="pre">...]</span></code>. This is convenient for display.</p>
</section>
<section id="weapon-and-armor">
<h2><span class="section-number">5.8. </span>Weapon and armor<a class="headerlink" href="#weapon-and-armor" title="Permalink to this headline"></a></h2>
<p>It’s convenient to have the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> easily tell you what weapon is currently wielded and what <em>armor</em> level all worn equipment provides. Otherwise you’d need to figure out what item is in which wield-slot and to add up armor slots manually every time you need to know.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/equipment.py </span>
<span class="kn">from</span> <span class="nn">.enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span><span class="p">,</span> <span class="n">Ability</span>
<span class="kn">from</span> <span class="nn">.objects</span> <span class="kn">import</span> <span class="n">get_bare_hand</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EquipmentHandler</span><span class="p">:</span>
<span class="c1"># ... </span>
<span class="nd">@property</span>
<span class="k">def</span> <span class="nf">armor</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="k">return</span> <span class="nb">sum</span><span class="p">(</span>
<span class="p">(</span>
<span class="c1"># armor is listed using its defense, so we remove 10 from it</span>
<span class="c1"># (11 is base no-armor value in Knave)</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BODY</span><span class="p">],</span> <span class="s2">&quot;armor&quot;</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span>
<span class="c1"># shields and helmets are listed by their bonus to armor</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">SHIELD_HAND</span><span class="p">],</span> <span class="s2">&quot;armor&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">),</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">HEAD</span><span class="p">],</span> <span class="s2">&quot;armor&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">),</span>
<span class="p">)</span>
<span class="p">)</span>
<span class="nd">@property</span>
<span class="k">def</span> <span class="nf">weapon</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="c1"># first checks two-handed wield, then one-handed; the two</span>
<span class="c1"># should never appear simultaneously anyhow (checked in `move` method).</span>
<span class="n">slots</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">slots</span>
<span class="n">weapon</span> <span class="o">=</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">TWO_HANDS</span><span class="p">]</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">weapon</span><span class="p">:</span>
<span class="n">weapon</span> <span class="o">=</span> <span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">WEAPON_HAND</span><span class="p">]</span>
<span class="c1"># if we still don&#39;t have a weapon, we return None here</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">weapon</span><span class="p">:</span>
<span class="o">~</span> <span class="n">weapon</span> <span class="o">=</span> <span class="n">get_bare_hands</span><span class="p">()</span>
<span class="k">return</span> <span class="n">weapon</span>
</pre></div>
</div>
<p>In the <code class="docutils literal notranslate"><span class="pre">.armor()</span></code> method we get the item (if any) out of each relevant wield-slot (body, shield, head), and grab their <code class="docutils literal notranslate"><span class="pre">armor</span></code> Attribute. We then <code class="docutils literal notranslate"><span class="pre">sum()</span></code> them all up.</p>
<p>In <code class="docutils literal notranslate"><span class="pre">.weapon()</span></code>, we simply check which of the possible weapon slots (weapon-hand or two-hands) have something in them. If not we fall back to the ‘Bare Hands’ object we created in the <a class="reference internal" href="Beginner-Tutorial-Objects.html#your-bare-hands"><span class="std std-doc">Object tutorial lesson</span></a> earlier.</p>
<section id="fixing-the-character-class">
<h3><span class="section-number">5.8.1. </span>Fixing the Character class<a class="headerlink" href="#fixing-the-character-class" title="Permalink to this headline"></a></h3>
<p>So we have added our equipment handler which validate what we put in it. This will however lead to a problem when we create things like NPCs in game, e.g. with</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>create/drop monster:evadventure.npcs.EvAdventureNPC
</pre></div>
</div>
<p>The problem is that when the/ monster is created it will briefly appear in your inventory before being dropped, so this code will fire on you when you do that (assuming you are an <code class="docutils literal notranslate"><span class="pre">EvAdventureCharacter</span></code>):</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/characters.py</span>
<span class="c1"># ... </span>
<span class="k">class</span> <span class="nc">EvAdventureCharacter</span><span class="p">(</span><span class="n">LivingMixin</span><span class="p">,</span> <span class="n">DefaultCharacter</span><span class="p">):</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">at_object_receive</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">moved_object</span><span class="p">,</span> <span class="n">source_location</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot; </span>
<span class="sd"> Called by Evennia when an object arrives &#39;in&#39; the character.</span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="bp">self</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">moved_object</span><span class="p">)</span>
</pre></div>
</div>
<p>This means that the equipmenthandler will check the NPC, and since it’s not a equippable thing, an <code class="docutils literal notranslate"><span class="pre">EquipmentError</span></code> will be raised, failing the creation. Since we want to be able to create npcs etc easily, we will handle this error with a <code class="docutils literal notranslate"><span class="pre">try...except</span></code> statement like so:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/characters.py</span>
<span class="c1"># ... </span>
<span class="kn">from</span> <span class="nn">evennia</span> <span class="kn">import</span> <span class="n">logger</span>
<span class="kn">from</span> <span class="nn">.equipment</span> <span class="kn">import</span> <span class="n">EquipmentError</span>
<span class="k">class</span> <span class="nc">EvAdventureCharacter</span><span class="p">(</span><span class="n">LivingMixin</span><span class="p">,</span> <span class="n">DefaultCharacter</span><span class="p">):</span>
<span class="c1"># ... </span>
<span class="k">def</span> <span class="nf">at_object_receive</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">moved_object</span><span class="p">,</span> <span class="n">source_location</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
<span class="w"> </span><span class="sd">&quot;&quot;&quot; </span>
<span class="sd"> Called by Evennia when an object arrives &#39;in&#39; the character.</span>
<span class="sd"> </span>
<span class="sd"> &quot;&quot;&quot;</span>
<span class="k">try</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">moved_object</span><span class="p">)</span>
<span class="k">except</span> <span class="n">EquipmentError</span><span class="p">:</span>
<span class="n">logger</span><span class="o">.</span><span class="n">log_trace</span><span class="p">()</span>
</pre></div>
</div>
<p>Using Evennia’s <code class="docutils literal notranslate"><span class="pre">logger.log_trace()</span></code> we catch the error and direct it to the server log. This allows you to see if there are real errors here as well, but once things work and these errors are spammy, you can also just replace the <code class="docutils literal notranslate"><span class="pre">logger.log_trace()</span></code> line with a <code class="docutils literal notranslate"><span class="pre">pass</span></code> to hide these errors.</p>
</section>
</section>
<section id="extra-credits">
<h2><span class="section-number">5.9. </span>Extra credits<a class="headerlink" href="#extra-credits" title="Permalink to this headline"></a></h2>
<p>This covers the basic functionality of the equipment handler. There are other useful methods that
can be added:</p>
<ul class="simple">
<li><p>Given an item, figure out which equipment slot it is currently in</p></li>
<li><p>Make a string representing the current loadout</p></li>
<li><p>Get everything in the backpack (only)</p></li>
<li><p>Get all wieldable items (weapons, shields) from backpack</p></li>
<li><p>Get all usable items (items with a use-location of <code class="docutils literal notranslate"><span class="pre">BACKPACK</span></code>) from the backpack</p></li>
</ul>
<p>Experiment with adding those. A full example is found in
<a class="reference internal" href="../../../api/evennia.contrib.tutorials.evadventure.equipment.html"><span class="doc std std-doc">evennia/contrib/tutorials/evadventure/equipment.py</span></a>.</p>
</section>
<section id="unit-testing">
<h2><span class="section-number">5.10. </span>Unit Testing<a class="headerlink" href="#unit-testing" title="Permalink to this headline"></a></h2>
<blockquote>
<div><p>Create a new module <code class="docutils literal notranslate"><span class="pre">mygame/evadventure/tests/test_equipment.py</span></code>.</p>
</div></blockquote>
<aside class="sidebar">
<p>See <a class="reference internal" href="../../../api/evennia.contrib.tutorials.evadventure.tests.test_equipment.html"><span class="doc std std-doc">evennia/contrib/tutorials/evadventure/tests/test_equipment.py</span></a>
for a finished testing example.</p>
</aside>
<p>To test the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code>, easiest is create an <code class="docutils literal notranslate"><span class="pre">EvAdventureCharacter</span></code> (this should by now
have <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code> available on itself as <code class="docutils literal notranslate"><span class="pre">.equipment</span></code>) and a few test objects; then test
passing these into the handler’s methods.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="c1"># mygame/evadventure/tests/test_equipment.py </span>
<span class="kn">from</span> <span class="nn">evennia.utils</span> <span class="kn">import</span> <span class="n">create</span>
<span class="kn">from</span> <span class="nn">evennia.utils.test_resources</span> <span class="kn">import</span> <span class="n">BaseEvenniaTest</span>
<span class="kn">from</span> <span class="nn">..objects</span> <span class="kn">import</span> <span class="n">EvAdventureObject</span><span class="p">,</span> <span class="n">EvAdventureHelmet</span><span class="p">,</span> <span class="n">EvAdventureWeapon</span>
<span class="kn">from</span> <span class="nn">..enums</span> <span class="kn">import</span> <span class="n">WieldLocation</span>
<span class="kn">from</span> <span class="nn">..characters</span> <span class="kn">import</span> <span class="n">EvAdventureCharacter</span>
<span class="k">class</span> <span class="nc">TestEquipment</span><span class="p">(</span><span class="n">BaseEvenniaTest</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">setUp</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">character</span> <span class="o">=</span> <span class="n">create</span><span class="o">.</span><span class="n">create_object</span><span class="p">(</span><span class="n">EvAdventureCharacter</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s1">&#39;testchar&#39;</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">helmet</span> <span class="o">=</span> <span class="n">create</span><span class="o">.</span><span class="n">create_object</span><span class="p">(</span><span class="n">EvAdventureHelmet</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s2">&quot;helmet&quot;</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">weapon</span> <span class="o">=</span> <span class="n">create</span><span class="o">.</span><span class="n">create_object</span><span class="p">(</span><span class="n">EvAdventureWeapon</span><span class="p">,</span> <span class="n">key</span><span class="o">=</span><span class="s2">&quot;weapon&quot;</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">test_add_remove</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">character</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">helmet</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span>
<span class="bp">self</span><span class="o">.</span><span class="n">character</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">],</span>
<span class="p">[</span><span class="bp">self</span><span class="o">.</span><span class="n">helmet</span><span class="p">]</span>
<span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">character</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">remove</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">helmet</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">assertEqual</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">character</span><span class="o">.</span><span class="n">equipment</span><span class="o">.</span><span class="n">slots</span><span class="p">[</span><span class="n">WieldLocation</span><span class="o">.</span><span class="n">BACKPACK</span><span class="p">],</span> <span class="p">[])</span>
<span class="c1"># ... </span>
</pre></div>
</div>
</section>
<section id="summary">
<h2><span class="section-number">5.11. </span>Summary<a class="headerlink" href="#summary" title="Permalink to this headline"></a></h2>
<p><em>Handlers</em> are useful for grouping functionality together. Now that we spent our time making the <code class="docutils literal notranslate"><span class="pre">EquipmentHandler</span></code>, we shouldn’t need to worry about item-slots anymore - the handler ‘handles’ all the details for us. As long as we call its methods, the details can be forgotten about.</p>
<p>We also learned to use <em>hooks</em> to tie <em>Knave</em>’s custom equipment handling into Evennia.</p>
<p>With <code class="docutils literal notranslate"><span class="pre">Characters</span></code>, <code class="docutils literal notranslate"><span class="pre">Objects</span></code> and now <code class="docutils literal notranslate"><span class="pre">Equipment</span></code> in place, we should be able to move on to character generation - where players get to make their own character!</p>
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