without edges</span>
            <span class="k">try</span><span class="p">:</span>
                <span class="c1"># up verts </span>
                <span class="n">U</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="n">LevelEdges</span><span class="p">[</span><span class="n">up_level</span><span class="p">])</span>
            <span class="k">except</span><span class="p">:</span>
                <span class="k">pass</span>

            <span class="k">try</s