lass="p">):</span>
        <span class="n">temp</span> <span class="o">=</span> <span class="p">[]</span>
        <span class="k">for</span> <span class="n">key</span> <span class="ow">in</span> <span class="nb">sorted</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">matrix</span><span class="o">.</span><span class="n">keys</span><span class="p">()):</span>
            <span class="n">subkeys</span> <span class="o">=</span> <span class="bp">self</span><span c