t;An abstract base class for all local descriptors.&quot;&quot;&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">periodic</span><span class="p">,</span> <span class="n">sparse</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=</span><span class="s2">&quot;float64&quot;</span><span class="p">,</span> <span class="n">average</span><span class="o">=</span><span clas