code: def is_csv_file(inputfile):
      
      try:
          stream = open(inputfile)
          row = stream.readline()
      except (IOError, UnicodeDecodeError):  # pragma: no cover
          return False
      finally:
          stream.close()
      content = row.strip().split(',')
      return inputfile.endswith('.csv') and len(content) >= 4
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).