    <span class="k">def</span> <span class="nf">derivatives_numerical</span><span class="p">(</span>
        <span class="bp">self</span><span class="p">,</span>
        <span class="n">d</span><span class="p">,</span>
        <span class="n">c</span><span class="p">,</span>
        <span class="n">system</span><span class="p">,</span>
        <span class="n">centers</span><span class="p">,</span>
        <span class="n">indices</span><span class="p">,</span>
        <span class="n">attach</span><span class