class="o">=</span> <span class="nb">sorted</span><span class="p">([</span><span class="nb">str</span><span class="p">(</span><span class="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="k">for</span> <span class="n">node</span> <span class="ow">in</span> <span class="n">ring</span><span class="p">])</span>
            <span class="c1"># All rings of interest are three-member rings</span>
          