title: json load only a single key value pair from all observations - python
body: <p>I have very large json files from which I would like to get a single key-value pair of all observations.
  eg.:</p>
  <pre><code>{&quot;name&quot;:&quot;John&quot;, &quot;rollno&quot;:4}
  </code></pre>
  <p>Suppose i have 10000 observations like this, I would like to extract only <code>rollno</code> from all the 10000 observations. How do I do this at the time of loading the file using <code>json.load()</code></p>