code: def atlas_inventory_count_missing( inv1, inv2 ):
      
      count = 0
      common = min(len(inv1), len(inv2))
      for i in xrange(0, common):
          for j in xrange(0, 8):
              if ((1 << (7 - j)) & ord(inv2[i])) != 0 and ((1 << (7 - j)) & ord(inv1[i])) == 0:
                  count += 1
  
      if len(inv1) < len(inv2):
          for i in xrange(len(inv1), len(inv2)):
              for j in xrange(0, 8):
                  if ((1 << (7 - j)) & ord(inv2[i])) != 0:
                      count += 1
  
      return count
docs: Find out how many bits are set in inv2 
      that are not set in inv1.