title: function not returning expected list
body: <p>I have 3 lists:</p>
  <pre><code>members = ['Alex', 'Danny', 'Kieran', 'Zoe', 'Caroline']
  visitors = ['Scott', 'Helen', 'Raj', 'Danny']
  signups = ['Helen', 'Scott']
  </code></pre>
  <p>The function should return a list of <code>visitors</code> who are neither existing nor new members. If there are none, return <code>None</code>.</p>
  <p>This is my code:</p>
  <pre><code>def guests(member,signup,visitor):
      visit = []
      for person in visitor:
          if person not in member and signup:
              visit.append(person)
              return visit
          return print(&quot;None.&quot;)
  </code></pre>
  <p>but my output returns <code>[&quot;Scott&quot;]</code>. I can't seem to figure what i haven't done right.</p>