title: Pandas XLSWriter - return instead of write
body: <p>I want to return an Excel file from my Flask (Python) server. This code:</p>
  
  <pre><code>writer = pd.ExcelWriter('filename.xlsx')
  dataframe.to_excel(writer, index=False)
  writer.save()
  </code></pre>
  
  <p>will write the Excel file to the file system. How can I <code>return</code> the file instead of writing it? </p>