擅长:python、mysql、java
<p><code>person not in member and signup</code>的计算结果为<code>(person not in member) and (signup)</code></p>
<p>当<code>person</code>为“Scott”时,第一部分为<code>True</code>,第二部分(<code>signup</code>)为非空列表,因此在布尔上下文中它被计算为<code>True</code>,因此整个条件为<code>True</code></p>
<p>然后,立即<code>return</code>输出,而无需进一步循环</p>
<p>你的意思是:</p>
<pre><code>def guests(member,signup,visitor):
visit = []
for person in visitor:
if person not in member and person not in signup:
visit.append(person)
return visit if len(visit) != 0 else None
</code></pre>