  <span class="n">carbons</span> <span class="o">=</span> <span class="p">[</span><span class="n">n</span> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">molgraph</span><span class="o">.</span><span class="n">graph</span><span class="o">.</span><span class="n">nodes</span> <span class="k">if</span>
                   <span class="nb">str</span><span class="p">(</span><span class="bp">self</span><span class="o