title: How to get the index value in pandas MultiIndex data frame?
body: <pre><code>df = pd.DataFrame({'a':[2,3,5], 'b':[1,2,3], 'c':[12,13,14]})
  df.set_index(['a','b'], inplace=True)
  display(df)
  s = df.iloc[1]
  # How to get 'a' and 'b' value from s? 
  </code></pre>
  
  <p>It is so annoying that ones columns become indices we cannot simply use df['colname'] to fetch values.</p>
  
  <p>Does it encourage we use <code>set_index(drop=False)</code>?</p>