title: Why does append return none
body: <pre><code>def num(x=[], y=[],result=[]):
      x.append(120), y.append(0)
      result.append(print(&quot;Progress&quot;))
      x.append(0), y.append(120)
      result.append(print(&quot;Exclude&quot;))
      print(len(result))
      print(result)
      num()
  </code></pre>