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<section class="sphx-glr-example-title" id="implementing-custom-wrappers">
<span id="sphx-glr-tutorials-gymnasium-basics-implementing-custom-wrappers-py"></span><h1>Implementing Custom Wrappers<a class="headerlink" href="#implementing-custom-wrappers" title="Permalink to this heading">#</a></h1>
<p>In this tutorial we will describe how to implement your own custom wrappers.
Wrappers are a great way to add functionality to your environments in a modular way.
This will save you a lot of boilerplate code.</p>
<p>We will show how to create a wrapper by</p>
<ul class="simple">
<li><p>Inheriting from <a class="reference internal" href="../../../api/wrappers/observation_wrappers/#gymnasium.ObservationWrapper" title="gymnasium.ObservationWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ObservationWrapper</span></code></a></p></li>
<li><p>Inheriting from <a class="reference internal" href="../../../api/wrappers/action_wrappers/#gymnasium.ActionWrapper" title="gymnasium.ActionWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ActionWrapper</span></code></a></p></li>
<li><p>Inheriting from <a class="reference internal" href="../../../api/wrappers/reward_wrappers/#gymnasium.RewardWrapper" title="gymnasium.RewardWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.RewardWrapper</span></code></a></p></li>
<li><p>Inheriting from <a class="reference internal" href="../../../api/wrappers/#gymnasium.Wrapper" title="gymnasium.Wrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.Wrapper</span></code></a></p></li>
</ul>
<p>Before following this tutorial, make sure to check out the docs of the <a class="reference internal" href="../../../api/wrappers/#module-gymnasium.wrappers" title="gymnasium.wrappers"><code class="xref py py-mod docutils literal notranslate"><span class="pre">gymnasium.wrappers</span></code></a> module.</p>
<section id="inheriting-from-gymnasium-observationwrapper">
<h2>Inheriting from <a class="reference internal" href="../../../api/wrappers/observation_wrappers/#gymnasium.ObservationWrapper" title="gymnasium.ObservationWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ObservationWrapper</span></code></a><a class="headerlink" href="#inheriting-from-gymnasium-observationwrapper" title="Permalink to this heading">#</a></h2>
<p>Observation wrappers are useful if you want to apply some function to the observations that are returned
by an environment. If you implement an observation wrapper, you only need to define this transformation
by implementing the <a class="reference internal" href="../../../api/wrappers/observation_wrappers/#gymnasium.ObservationWrapper.observation" title="gymnasium.ObservationWrapper.observation"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.ObservationWrapper.observation()</span></code></a> method. Moreover, you should remember to
update the observation space, if the transformation changes the shape of observations (e.g. by transforming
dictionaries into numpy arrays, as in the following example).</p>
<p>Imagine you have a 2D navigation task where the environment returns dictionaries as observations with
keys <code class="docutils literal notranslate"><span class="pre">&quot;agent_position&quot;</span></code> and <code class="docutils literal notranslate"><span class="pre">&quot;target_position&quot;</span></code>. A common thing to do might be to throw away some degrees of
freedom and only consider the position of the target relative to the agent, i.e.
<code class="docutils literal notranslate"><span class="pre">observation[&quot;target_position&quot;]</span> <span class="pre">-</span> <span class="pre">observation[&quot;agent_position&quot;]</span></code>. For this, you could implement an
observation wrapper like this:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">numpy</span> <span class="k">as</span> <span class="nn">np</span>
<span class="kn">from</span> <span class="nn">gym</span> <span class="kn">import</span> <span class="n">ActionWrapper</span><span class="p">,</span> <span class="n">ObservationWrapper</span><span class="p">,</span> <span class="n">RewardWrapper</span><span class="p">,</span> <span class="n">Wrapper</span>
<span class="kn">import</span> <span class="nn">gymnasium</span> <span class="k">as</span> <span class="nn">gym</span>
<span class="kn">from</span> <span class="nn">gymnasium.spaces</span> <span class="kn">import</span> <span class="n">Box</span><span class="p">,</span> <span class="n">Discrete</span>
<span class="k">class</span> <span class="nc">RelativePosition</span><span class="p">(</span><span class="n">ObservationWrapper</span><span class="p">):</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">env</span><span class="p">):</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="n">env</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">observation_space</span> <span class="o">=</span> <span class="n">Box</span><span class="p">(</span><span class="n">shape</span><span class="o">=</span><span class="p">(</span><span class="mi">2</span><span class="p">,),</span> <span class="n">low</span><span class="o">=-</span><span class="n">np</span><span class="o">.</span><span class="n">inf</span><span class="p">,</span> <span class="n">high</span><span class="o">=</span><span class="n">np</span><span class="o">.</span><span class="n">inf</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">observation</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">obs</span><span class="p">):</span>
<span class="k">return</span> <span class="n">obs</span><span class="p">[</span><span class="s2">&quot;target&quot;</span><span class="p">]</span> <span class="o">-</span> <span class="n">obs</span><span class="p">[</span><span class="s2">&quot;agent&quot;</span><span class="p">]</span>
</pre></div>
</div>
</section>
<section id="inheriting-from-gymnasium-actionwrapper">
<h2>Inheriting from <a class="reference internal" href="../../../api/wrappers/action_wrappers/#gymnasium.ActionWrapper" title="gymnasium.ActionWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ActionWrapper</span></code></a><a class="headerlink" href="#inheriting-from-gymnasium-actionwrapper" title="Permalink to this heading">#</a></h2>
<p>Action wrappers can be used to apply a transformation to actions before applying them to the environment.
If you implement an action wrapper, you need to define that transformation by implementing
<a class="reference internal" href="../../../api/wrappers/action_wrappers/#gymnasium.ActionWrapper.action" title="gymnasium.ActionWrapper.action"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.ActionWrapper.action()</span></code></a>. Moreover, you should specify the domain of that transformation
by updating the action space of the wrapper.</p>
<p>Lets say you have an environment with action space of type <a class="reference internal" href="../../../api/spaces/fundamental/#gymnasium.spaces.Box" title="gymnasium.spaces.Box"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.spaces.Box</span></code></a>, but you would only like
to use a finite subset of actions. Then, you might want to implement the following wrapper:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DiscreteActions</span><span class="p">(</span><span class="n">ActionWrapper</span><span class="p">):</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">env</span><span class="p">,</span> <span class="n">disc_to_cont</span><span class="p">):</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="n">env</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">disc_to_cont</span> <span class="o">=</span> <span class="n">disc_to_cont</span>
<span class="bp">self</span><span class="o">.</span><span class="n">action_space</span> <span class="o">=</span> <span class="n">Discrete</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">disc_to_cont</span><span class="p">))</span>
<span class="k">def</span> <span class="nf">action</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">act</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">disc_to_cont</span><span class="p">[</span><span class="n">act</span><span class="p">]</span>
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s2">&quot;__main__&quot;</span><span class="p">:</span>
<span class="n">env</span> <span class="o">=</span> <span class="n">gym</span><span class="o">.</span><span class="n">make</span><span class="p">(</span><span class="s2">&quot;LunarLanderContinuous-v2&quot;</span><span class="p">)</span>
<span class="n">wrapped_env</span> <span class="o">=</span> <span class="n">DiscreteActions</span><span class="p">(</span>
<span class="n">env</span><span class="p">,</span> <span class="p">[</span><span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">]),</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">]),</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">]),</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">0</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">])]</span>
<span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">wrapped_env</span><span class="o">.</span><span class="n">action_space</span><span class="p">)</span> <span class="c1"># Discrete(4)</span>
</pre></div>
</div>
</section>
<section id="inheriting-from-gymnasium-rewardwrapper">
<h2>Inheriting from <a class="reference internal" href="../../../api/wrappers/reward_wrappers/#gymnasium.RewardWrapper" title="gymnasium.RewardWrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.RewardWrapper</span></code></a><a class="headerlink" href="#inheriting-from-gymnasium-rewardwrapper" title="Permalink to this heading">#</a></h2>
<p>Reward wrappers are used to transform the reward that is returned by an environment.
As for the previous wrappers, you need to specify that transformation by implementing the
<a class="reference internal" href="../../../api/wrappers/reward_wrappers/#gymnasium.RewardWrapper.reward" title="gymnasium.RewardWrapper.reward"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.RewardWrapper.reward()</span></code></a> method. Also, you might want to update the reward range of the wrapper.</p>
<p>Let us look at an example: Sometimes (especially when we do not have control over the reward
because it is intrinsic), we want to clip the reward to a range to gain some numerical stability.
To do that, we could, for instance, implement the following wrapper:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">SupportsFloat</span>
<span class="k">class</span> <span class="nc">ClipReward</span><span class="p">(</span><span class="n">RewardWrapper</span><span class="p">):</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">env</span><span class="p">,</span> <span class="n">min_reward</span><span class="p">,</span> <span class="n">max_reward</span><span class="p">):</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="n">env</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">min_reward</span> <span class="o">=</span> <span class="n">min_reward</span>
<span class="bp">self</span><span class="o">.</span><span class="n">max_reward</span> <span class="o">=</span> <span class="n">max_reward</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reward_range</span> <span class="o">=</span> <span class="p">(</span><span class="n">min_reward</span><span class="p">,</span> <span class="n">max_reward</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">reward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">r</span><span class="p">:</span> <span class="n">SupportsFloat</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">SupportsFloat</span><span class="p">:</span>
<span class="k">return</span> <span class="n">np</span><span class="o">.</span><span class="n">clip</span><span class="p">(</span><span class="n">r</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">min_reward</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">max_reward</span><span class="p">)</span>
</pre></div>
</div>
</section>
<section id="inheriting-from-gymnasium-wrapper">
<h2>Inheriting from <a class="reference internal" href="../../../api/wrappers/#gymnasium.Wrapper" title="gymnasium.Wrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.Wrapper</span></code></a><a class="headerlink" href="#inheriting-from-gymnasium-wrapper" title="Permalink to this heading">#</a></h2>
<p>Sometimes you might need to implement a wrapper that does some more complicated modifications (e.g. modify the
reward based on data in <code class="docutils literal notranslate"><span class="pre">info</span></code> or change the rendering behavior).
Such wrappers can be implemented by inheriting from <a class="reference internal" href="../../../api/wrappers/#gymnasium.Wrapper" title="gymnasium.Wrapper"><code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.Wrapper</span></code></a>.</p>
<ul class="simple">
<li><p>You can set a new action or observation space by defining <code class="docutils literal notranslate"><span class="pre">self.action_space</span></code> or <code class="docutils literal notranslate"><span class="pre">self.observation_space</span></code> in <code class="docutils literal notranslate"><span class="pre">__init__</span></code>, respectively</p></li>
<li><p>You can set new metadata and reward range by defining <code class="docutils literal notranslate"><span class="pre">self.metadata</span></code> and <code class="docutils literal notranslate"><span class="pre">self.reward_range</span></code> in <code class="docutils literal notranslate"><span class="pre">__init__</span></code>, respectively</p></li>
<li><p>You can override <a class="reference internal" href="../../../api/wrappers/#gymnasium.Wrapper.step" title="gymnasium.Wrapper.step"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.Wrapper.step()</span></code></a>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.Wrapper.render()</span></code>, <a class="reference internal" href="../../../api/wrappers/#gymnasium.Wrapper.close" title="gymnasium.Wrapper.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">gymnasium.Wrapper.close()</span></code></a> etc.</p></li>
</ul>
<p>If you do this, you can access the environment that was passed
to your wrapper (which <em>still</em> might be wrapped in some other wrapper) by accessing the attribute <code class="xref py py-attr docutils literal notranslate"><span class="pre">env</span></code>.</p>
<p>Lets also take a look at an example for this case. Most MuJoCo environments return a reward that consists
of different terms: For instance, there might be a term that rewards the agent for completing the task and one term that
penalizes large actions (i.e. energy usage). Usually, you can pass weight parameters for those terms during
initialization of the environment. However, <em>Reacher</em> does not allow you to do this! Nevertheless, all individual terms
of the reward are returned in <cite>info</cite>, so let us build a wrapper for Reacher that allows us to weight those terms:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">ReacherRewardWrapper</span><span class="p">(</span><span class="n">Wrapper</span><span class="p">):</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">env</span><span class="p">,</span> <span class="n">reward_dist_weight</span><span class="p">,</span> <span class="n">reward_ctrl_weight</span><span class="p">):</span>
<span class="nb">super</span><span class="p">()</span><span class="o">.</span><span class="fm">__init__</span><span class="p">(</span><span class="n">env</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reward_dist_weight</span> <span class="o">=</span> <span class="n">reward_dist_weight</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reward_ctrl_weight</span> <span class="o">=</span> <span class="n">reward_ctrl_weight</span>
<span class="k">def</span> <span class="nf">step</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">action</span><span class="p">):</span>
<span class="n">obs</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">terminated</span><span class="p">,</span> <span class="n">truncated</span><span class="p">,</span> <span class="n">info</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">env</span><span class="o">.</span><span class="n">step</span><span class="p">(</span><span class="n">action</span><span class="p">)</span>
<span class="n">reward</span> <span class="o">=</span> <span class="p">(</span>
<span class="bp">self</span><span class="o">.</span><span class="n">reward_dist_weight</span> <span class="o">*</span> <span class="n">info</span><span class="p">[</span><span class="s2">&quot;reward_dist&quot;</span><span class="p">]</span>
<span class="o">+</span> <span class="bp">self</span><span class="o">.</span><span class="n">reward_ctrl_weight</span> <span class="o">*</span> <span class="n">info</span><span class="p">[</span><span class="s2">&quot;reward_ctrl&quot;</span><span class="p">]</span>
<span class="p">)</span>
<span class="k">return</span> <span class="n">obs</span><span class="p">,</span> <span class="n">reward</span><span class="p">,</span> <span class="n">terminated</span><span class="p">,</span> <span class="n">truncated</span><span class="p">,</span> <span class="n">info</span>
</pre></div>
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<li><a class="reference internal" href="#">Implementing Custom Wrappers</a><ul>
<li><a class="reference internal" href="#inheriting-from-gymnasium-observationwrapper">Inheriting from <code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ObservationWrapper</span></code></a></li>
<li><a class="reference internal" href="#inheriting-from-gymnasium-actionwrapper">Inheriting from <code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.ActionWrapper</span></code></a></li>
<li><a class="reference internal" href="#inheriting-from-gymnasium-rewardwrapper">Inheriting from <code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.RewardWrapper</span></code></a></li>
<li><a class="reference internal" href="#inheriting-from-gymnasium-wrapper">Inheriting from <code class="xref py py-class docutils literal notranslate"><span class="pre">gymnasium.Wrapper</span></code></a></li>
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