擅长:python、mysql、java
<p>初始化<code>sum</code>的<code>start</code>参数为<code>Item</code>类型的对象,因为它的默认值是<code>int</code>类型的对象,如<a href="https://docs.python.org/3/library/functions.html#sum" rel="nofollow noreferrer">docs</a>:<code>sum(iterable, /, start=0)</code>中所述,其中<code>0</code>是<code>int</code></p>
<pre><code>print(sum([Item(2), Item(4)], start=Item(0)).factor)
</code></pre>