Python实现把数字转换成中文

周末在家，写了个小程序，用于将阿拉伯数字转换化大写中文。程序没经过任何优化，出没经过详细的测试，挂到网上，方便将来有需要的时候直接拿来用。

    #!/usr/bin/python
    #-*- encoding: utf-8 -*-

    import types

    class NotIntegerError(Exception):
      pass

    class OutOfRangeError(Exception):
      pass

    _MAPPING = (u'零', u'一', u'二', u'三', u'四', u'五', u'六', u'七', u'八', u'九', )
    _P0 = (u'', u'十', u'百', u'千', )
    _S4, _S8, _S16 = 10 ** 4 , 10 ** 8, 10 ** 16
    _MIN, _MAX = 0, 9999999999999999

    def _to_chinese4(num):
      '''转换[0, 10000)之间的阿拉伯数字
      '''
      assert(0 <= num and num < _S4)
      if num < 10:
        return _MAPPING[num]
      else:
        lst = [ ]
        while num >= 10:
          lst.append(num % 10)
          num = num / 10
        lst.append(num)
        c = len(lst)  # 位数
        result = u''

        for idx, val in enumerate(lst):
          if val != 0:
            result += _P0[idx] + _MAPPING[val]
            if idx < c - 1 and lst[idx + 1] == 0:
              result += u'零'

        return result[::-1].replace(u'一十', u'十')

    def _to_chinese8(num):
      assert(num < _S8)
      to4 = _to_chinese4
      if num < _S4:
        return to4(num)
      else:
        mod = _S4
        high, low = num / mod, num % mod
        if low == 0:
          return to4(high) + u'万'
        else:
          if low < _S4 / 10:
            return to4(high) + u'万零' + to4(low)
          else:
            return to4(high) + u'万' + to4(low)

    def _to_chinese16(num):
      assert(num < _S16)
      to8 = _to_chinese8
      mod = _S8
      high, low = num / mod, num % mod
      if low == 0:
        return to8(high) + u'亿'
      else:
        if low < _S8 / 10:
          return to8(high) + u'亿零' + to8(low)
        else:
          return to8(high) + u'亿' + to8(low)

    def to_chinese(num):
      if type(num) != types.IntType and type(num) != types.LongType:
        raise NotIntegerError(u'%s is not a integer.' % num)
      if num < _MIN or num > _MAX:
        raise OutOfRangeError(u'%d out of range[%d, %d)' % (num, _MIN, _MAX))

      if num < _S4:
        return _to_chinese4(num)
      elif num < _S8:
        return _to_chinese8(num)
      else:
        return _to_chinese16(num)

    if __name__ == '__main__':
      print to_chinese(9000)