title: json.loads allows duplicate keys in a dictionary, overwriting the first value
body: <pre><code>&gt;&gt;&gt; raw_post_data = request.raw_post_data
  &gt;&gt;&gt; print raw_post_data
  {"group":{"groupId":"2", "groupName":"GroupName"}, "members":{"1":{"firstName":"fName","lastName":"LName","address":"address"},"1": {"firstName":"f_Name","lastName":"L_Name","address":"_address"}}}
  &gt;&gt;&gt; create_request = json.loads(raw_post_data)
  &gt;&gt;&gt; print create_request
  {u'group': {u'groupName': u'GroupName', u'groupId': u'2'}, u'members': {u'1': {u'lastName': u'L_Name', u'firstName': u'f_Name', u'address': u'_address'}}}
  </code></pre>
  
  <p>As you can see members with key '1' is overwritten when I use <code>json.dumps()</code></p>
  
  <p>Is there any way to catch it as exception in python, saying found duplicate keys in request from client ?</p>