code: def DFReader_is_text_log(filename):
      '''return True if a file appears to be a valid text log'''
      f = open(filename)
      ret = (f.read(8000).find('FMT, ') != -1)
      f.close()
      return ref DFReader_is_text_log(filename):
      '''return True if a file appears to be a valid text log'''
      f = open(filename)
      ret = (f.read(8000).find('FMT, ') != -1)
      f.close()
      return ret
docs: return True if a file appears to be a valid text log