title: Automatically rename columns to ensure they are unique
body: <p>I fetch a spreadsheet into a Python DataFrame named <code>df</code>.</p>
  
  <p>Let's give a sample:</p>
  
  <pre><code>df=pd.DataFrame({'a': np.random.rand(10), 'b': np.random.rand(10)})
  df.columns=['a','a']
  
            a         a
  0  0.973858  0.036459
  1  0.835112  0.947461
  2  0.520322  0.593110
  3  0.480624  0.047711
  4  0.643448  0.104433
  5  0.961639  0.840359
  6  0.848124  0.437380
  7  0.579651  0.257770
  8  0.919173  0.785614
  9  0.505613  0.362737
  </code></pre>
  
  <p>When I run <code>df.columns.is_unique</code> I get <code>False</code></p>
  
  <p>I would like to automatically rename column 'a' to 'a_2' (or things like that)</p>
  
  <p>I don't expect a solution like <code>df.columns=['a','a_2']</code></p>
  
  <p>I looking for a solution that could be usable for several columns!</p>