title: Renaming columns in a Pandas dataframe with duplicate column names?
body: <p>I have a df X with columns with duplicate names: </p>
  
  <pre><code>In [77]: X_R
  Out[77]: 
        dollars  dollars
     0   0.7085   0.5000
  </code></pre>
  
  <p>I want to rename it so that I have: </p>
  
  <pre><code>In [77]: X_R
  Out[77]: 
         Retail   Cost
     0   0.7085   0.5000
  </code></pre>
  
  <p>Using the Pandas rename function does' work: </p>
  
  <pre><code>X_R.rename(index=str, columns={"dollars": "Retail", "dollars": "Cost"})
  </code></pre>
  
  <p>Just gives me two columns named Cost. </p>
  
  <p>How can I rename the columns in this case? </p>