如何理解这段校验和算法 Python 代码？

<span class="k">def</span> <span class="nf">checksum</span><span class="p">(</span><span class="n">data</span><span class="p">):</span>
    <span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">data</span><span class="p">)</span> <span class="o">%</span> <span class="mi">2</span><span class="p">:</span>
        <span class="n">data</span> <span class="o">+=</span> <span class="n">b</span><span class="s">'</span><span class="se">\x00</span><span class="s">'</span>
    <span class="n">s</span> <span class="o">=</span> <span class="nb">sum</span><span class="p">(</span><span class="n">array</span><span class="o">.</span><span class="n">array</span><span class="p">(</span><span class="s">'H'</span><span class="p">,</span><span class="n">data</span><span class="p">))</span>
    <span class="n">s</span> <span class="o">=</span> <span class="p">(</span><span class="n">s</span> <span class="o">&</span> <span class="mh">0xffff</span><span class="p">)</span> <span class="o">+</span> <span class="p">(</span><span class="n">s</span> <span class="o">>></span> <span class="mi">16</span><span class="p">)</span>
    <span class="n">s</span> <span class="o">+=</span> <span class="p">(</span><span class="n">s</span> <span class="o">>></span> <span class="mi">16</span><span class="p">)</span>
    <span class="k">return</span> <span class="n">_socket</span><span class="o">.</span><span class="n">ntohs</span><span class="p">(</span><span class="o">~</span><span class="n">s</span> <span class="o">&</span> <span class="mh">0xffff</span><span class="p">)</span>