code: def followingPrefix(prefix):
          prefixBytes = array('B', prefix)
          changeIndex = len(prefixBytes) - 1
          while (changeIndex >= 0 and prefixBytes[changeIndex] == 0xff ):
              changeIndex = changeIndex - 1;
          if(changeIndex < 0):
              return None
          newBytes = array('B', prefix[0:changeIndex + 1])
          newBytes[changeIndex] = newBytes[changeIndex] + 1
          return newBytes.tostring()