title: Find if nested key exists in json python
body: <p>In the following JSON response, what's the proper way to check if the nested key "C" exists in python 2.7?</p>
  
  <pre><code>{
    "A": {
      "B": {
        "C": {"D": "yes"}
           }
         }
  }
  </code></pre>
  
  <p>one line JSON
      { "A": { "B": { "C": {"D": "yes"} } } }</p>