title: Rename Pandas dataframe with NaN header
body: <p>i currently work with dataframes, and i'm stacking them thus to achieve specific format. I have a question i'm trying to change name of the header but it doesn't work ( by using.. .rename(columns={'NaN'='type', inplace=True), same thing im trying to change the name of columns '6' to Another with the same principe as mentioned. </p>
  
  <p>Here:                                    </p>
  
  <pre><code>                                               NaN Quantity
  6                                                                 
  01/06                       KULUTUS - CONSUMPTION  8976.27     
  01/06  TEOLLISUUSKULUTUS - INDUSTRIAL CONSUMPTION  4121.36    
  01/06             MUU KULUTUS - OTHER CONSUMPTION  4854.91
  </code></pre>