title: Pandas: difference between NaN and None
body: <p>What's the difference between a cell value of <code>NaN</code> and <code>None</code>? I used <code>df.dropna()</code>, which drops all <code>NaN</code> but I still have a lot of <code>None</code>. </p>
  
  <p>I am wondering what's the difference between them and how do I get rid of <code>None</code> as well?</p>
  
  <p>Thanks!</p>