an class="kc">None</span><span class="p">:</span>
<span class="w">        </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Main program start with extracting the periodic frequent items from the database and</span>
<span class="sd">        performs prefix equivalence to form the combinations and generates partial-periodic patterns.</span>
<span class="sd">        :return: None</span>

<span class="sd">        &quot;&quot;&quot;</span>
        <span class="bp">self</span><span class