an class="n">seen</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span
            class="n">u</span><span class="p">)</span>
            <span class="n">edge_tour</span><span class="o">.</span><span class="n">append</span><span
            class="p">((</span><span class="n">u</span><span class="p">,</span> <span class="n">u</span><span class="p">))</span>
        <span class="n">edge_tour</span><span class="o">.</span><span class="n">append</span><span
            class="p"