code: def is_excel_file(inputfile):
      
      try:
          xlrd.open_workbook(inputfile)
      except Exception as err:
          print(err)
          return False
      return True
docs: Return whether the provided file is a CSV file or not.
      This checks if the first row of the file can be splitted by ',' and
      if the resulting line contains more than 4 columns (Markers, linkage
      group, chromosome, trait).