擅长:python、mysql、java
<p><code>.append</code>返回<code>none</code>,这就是您将<code>number_list</code>设置为的内容。相反,使用该方法时不要将其设置为<code>number_list</code>,这样可以很好地工作</p>
<pre class="lang-py prettyprint-override"><code>>>> number_list = [1,2,3,4,5,6,7,8]
>>> number_list
[1, 2, 3, 4, 5, 6, 7, 8]
>>> number_list.append(number_list[-1]+1)
>>> number_list
[1, 2, 3, 4, 5, 6, 7, 8, 9]
</code></pre>
<blockquote>
<p>You might have noticed that methods like insert, remove or sort that only modify the list have no return value printed – they return the default None. 1 This is a design principle for all mutable data structures in Python. [<a href="https://docs.python.org/3.7/tutorial/datastructures.html#more-on-lists" rel="nofollow noreferrer">source</a>]</p>
</blockquote>