title: Python function prints None
body: <p>I have the following exercise:</p>
  
  <blockquote>
    <p>The parameter weekday is True if it is
    a weekday, and the parameter vacation
    is True if we are on vacation. We
    sleep in if it is not a weekday or
    we're on vacation. Return True if we
    sleep in.</p>
  </blockquote>
  
  <p>Here's what I've done, but the second print function only prints <code>'None'</code>.</p>
  
  <pre><code>def sleep_in(weekday, vacation):
      if(not weekday or vacation):
          return True
  
  print(sleep_in(False, False))
  print(sleep_in(True, False))
  print(sleep_in(False, True))
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>True
  None
  True
  </code></pre>