    <span class="k">yield</span> <span class="n">current</span>
            <span class="n">current</span> <span class="o">=</span> <span class="n">current</span><span
            class="o">.</span><span class="n">suc</span>

    <span class="k">def</span> <span class="nf">__copy__</span><span class="p">(</span><span class="bp">self</span><span
            class="p">):</span>
        <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Only use to write data, only need data of root and recurs