title: Datastore operation timed out during excel file generation
body: <p>I'm generating an excel file using xlwt and store it on datastore as blob property. But during the generation got this error <code>"Timeout: The datastore operation timed out, or the data was temporarily unavailable."</code>.</p>
  
  <p>I have noticed that using xlutils we can update the exsisting files. I'm planning to do something like this, first time i will craete the file with half of my data and using another task will complete the file creation.</p>
  
  <p>is there any better way to do this ?</p>
  
  <p>Here is my current code: </p>
  
  <pre><code>from xlwt import *
  wb = Workbook()
  ws0 = wb.add_sheet("Sheet 1")
  
  style = XFStyle()
  style.font.name = 'Tahoma'   
  
  currency_style = XFStyle()
  currency_style.num_format_str = '$#,##0.00'       
  
  ws0.write(0, 0, 'Col 1', style)
  ws0.write(0, 1, 'Col 2', style)
  ws0.write(0, 2, 'Col 3', style)
  ws0.write(0, 3, 'Col 4', style)
  rx = 1
  
  for each in db_result:                
        ws0.write(rx, 0, each.col1, style)
        ws0.write(rx, 1, each.col2, style)
        ws0.write(rx, 2, each.col3, style)
  
        try:
            ws0.write(rx, 3, round(float(each.col4), 2), currency_style)
        except:
            ws0.write(rx, 3, each.col4, style)
  
        rx = rx + 1                
        db.delete(each)
  
  buffer = StringIO.StringIO()
  wb.save(buffer)
  contents = buffer.getvalue()
  
  f = myfile()
  f.name = 'File 1'
  f.file = db.Blob(contents)
  f.put()
  </code></pre>