an> <span class="o">=</span> <span class="p">[]</span>
                    <span class="n">coords_des</span> <span class="o">=</span> <span class="p">[]</span>
                <span class="k">else</span><span class="p">:</span>
                    <span class="n">descriptors</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">empty</span><span class="p">(</span><span class="n">shape_des</span><span class="p">,</span> <span class="n">dtype</span><span class="o">=<