title: Add prefix to specific columns of Dataframe
body: <p>I've a DataFrame like that :</p>
  
  <pre><code>col1   col2   col3   col4   col5   col6   col7   col8
  0      5345   rrf    rrf    rrf    rrf    rrf    rrf
  1      2527   erfr   erfr   erfr   erfr   erfr   erfr
  2      2727   f      f      f      f      f      f
  </code></pre>
  
  <p>I would like to rename all columns but not <strong>col1</strong> and <strong>col2</strong>.</p>
  
  <p>So I tried to make a loop</p>
  
  <pre><code>print(df.columns)
      for col in df.columns:
          if col != 'col1' and col != 'col2':
              col.rename = str(col) + '_x'
  </code></pre>
  
  <p>But it's not very efficient...it doesn't work !</p>