pan class="n">key</span> <span class="ow">not</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">matrix</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">matrix</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="p">{</span><span class="n">subkey</span><span class="p">:</span> <span class="mi">1</span><span class="p">}</span>
     