><span class="n">columns</span><span class="p">)</span>
        <span class="c1"># Loop to change one feature at a time, then two features, and so on.</span>
        <span class="k">for</span> <span class="n">num_features_to_vary</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">features_to_vary</span><sp