code: def index(self, item):
          
          item = self._cast(item)
          offset = item - self.startIp
          if offset >= 0 and offset < self._len:
              return offset
          raise ValueError('%s is not in range' % self._ipver.long2ip(item))
docs: Return the 0-based position of `item` in this IpRange.
  
  
          >>> r = IpRange('127.0.0.1', '127.255.255.255')
          >>> r.index('127.0.0.1')
          0
          >>> r.index('127.255.255.255')
          16777214
          >>> r.index('10.0.0.1')
          Traceback (most recent call last):
              ...
          ValueError: 10.0.0.1 is not in range
  
  
          :param item: Dotted-quad ip address.
          :type item: str
          :returns: Index of ip address in range