title: Python: Openpyxl outputs "None" for empty cells
body: <p>The below code should go through directories, open files, convert etc. The thing is when a cell is empty, the resulting CSV file outputs "None" in its place.</p>
  
  <p>Any reason why and can this be remedied?</p>
  
  <p>Thanks</p>
  
  <pre><code>import os
  from openpyxl import load_workbook
  import csv
  
  for subdir, dirs, files in os.walk("C:\Users\Alan\Downloads\Knowledge\HOW DO I"):
      for file in files:
          filepath = subdir + os.sep + file
  
          wb = load_workbook(filename=filepath)
          sh = wb.active
          your_csv_file = open(filepath.replace(".xlsx","")+'_csv.csv','wb')
          wr = csv.writer(your_csv_file,quoting=csv.QUOTE_ALL)
  
          for rownum in sh.iter_rows():
              wr.writerow([unicode(val.value).encode('ascii','ignore') for val in rownum])
  
          your_csv_file.close()
  </code></pre>