n> <span class="o">=</span> <span class="n">st</span> <span class="o">-</span> <span class="mi">1</span>
        <span class="k">while</span> <span class="n">j</span> <span class="o">&gt;=</span> <span class="mi">0</span> <span class="ow">and</span> <span class="nb">len</span><span class="p">(</span><span class="n">pre_idxs</span><span class="p">)</span> <span class="o">&lt;</span> <span class="n">context</span><span class="p">:</span>
            <span class="k">if</span> <span class="ow">not</span> <span 