title: invalid literal for int() with base 10: ''
body: <p>I met a problem "invalid literal for int() with base 10: '' ", which means python cannot convert '' to integers. But I have already added a condition <code>if(sh.cell_value(rowx=rx, colx=3)!=''):</code>, which could skip the blocks which contains nothing in the excel. Does anyone have some idea? Thank you very much!</p>
  
  <pre><code>import xlrd
  book = xlrd.open_workbook("streeteasy.xls")
  sh = book.sheet_by_index(0)
  total = 0
  
  for rx in range (sh.nrows):
      if(sh.cell_value(rowx=rx, colx=3)!=''):
          s = sh.cell_value(rowx=rx, colx=3)
          print filter(unicode.isdigit, s)
          print int(filter(unicode.isdigit, s))
          total += int(filter(unicode.isdigit, s))
  </code></pre>