 checking that.</span>
        <span class="k">try</span><span class="p">:</span>
            <span class="n">n_low</span> <span class="o">=</span> <span class="nb">min</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">f</span><span class="o">.</span><span class="n">values</span><span class="p">())</span>
            <span class="n">n_high</span> <span class="o">=</span> <span class="nb">max</span><span class="p">(</span><span class="bp">self</span><span class