title: Indexing is not properly working in pandas dataframe
body: <p>I have the following data frame with itemid column is bold when printed in the notebook.</p>
  
  <pre><code>itemid   |  user_id  | day1   | day2      
  0        |  1232     | 5      | 3
  1        |  4107     | 5      | 3
  2        |  9262     | 5      | 3
  3        |  1031     | 5      | 3
  </code></pre>
  
  <p>Then I reset the its index using this:</p>
  
  <pre><code>df.index.name = None
  </code></pre>
  
  <p>But, then I still have the same dataframe. Then, I reset its index using:</p>
  
  <pre><code>df= df.set_index('user_id')
  </code></pre>
  
  <p>Then, I get this:</p>
  
  <pre><code>item_id  | day1   | day2    
  user_id  
  1232     | 5      | 3
  4107     | 5      | 3
  9262     | 5      | 3
  1031     | 5      | 3
  </code></pre>
  
  <p>I have no idea why <code>item_id</code> still stays there. Any ideas?</p>