title: How to replace Nan to None in json file via python?
body: <p>Suppose here is a unknown json file.</p>
  
  <pre><code>data = json.loads(file)
  </code></pre>
  
  <p>It might looks like:</p>
  
  <pre><code>data = [
  {"key1":"xxx","key2":"yyy","key3":"zzz"},
  {"key1":"xxx","key2":Nan,"key3":"zzz"},
  {"key1":"xxx","key2":"yyy","key3":Nan}
  ]
  </code></pre>
  
  <p>I want to change the value Nan to None.<br>
  What I did now is using a for loop and check every key's value. It looks stupid...<br>
  Are there a simple way to replace Nan to None? For example in pandas, we can use <code>df.replace</code> easily.</p>