code: def nti(self, s):
          
          # There are two possible encodings for a number field, see
          # itn() below.
          if s[0] != chr(0x80):
              try:
                  n = int(self.nts(s) or "0", 8)
              except ValueError:
                  raise ValueError("invalid tar header")
          else:
              n = 0
              for i in xrange(len(s) - 1):
                  n <<= 8
                  n += ord(s[i + 1])
          return n
docs: Convert a number field to a python number.