"bp">self</span><span class="o">.</span><span class="n">species</span><span class="p">[</span><span class="n">node</span><span class="p">])</span> <span class="ow">not</span> <span class="ow">in</span> <span class="p">[</span><span class="s2">&quot;C&quot;</span><span class="p">,</span> <span class="s2">&quot;H&quot;</span><span class="p">]:</span>
                    <span class="n">heteroatoms</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">node</span><span 