title: writing pandas df to file using variable as file name
body: <p>I am trying to write pandas df to an output file with:</p>
  
  <pre><code>outFileName="myfile_" + gene_name #gene_name gets a new value from argparse 
  
  df.to_csv('%.csv' %outFileName, sep=',', index=False)
  </code></pre>
  
  <p>the error I am getting::</p>
  
  <pre><code>TypeError: %c requires int or char
  </code></pre>
  
  <p>I tried </p>
  
  <pre><code>outFileName=str("myfile_" + gene_name)
  </code></pre>
  
  <p>and got the same error. Am I missing something? I can save the df if I do not use variable as outputfile name but I need to have the variable. </p>