f</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span
            class="p">,</span> <span class="n">root</span><span class="o">=</span><span class="kc">None</span><span
            class="p">,</span> <span class="n">first</span><span class="o">=</span><span class="kc">None</span><span
            class="p">,</span> <span class="n">last</span><span class="o">=</span><span class="kc">None</span><span
            class="p">,</span> <span class="n">weight</span><spa