code: def webIDToStoreID(key, webid):
      
      if len(webid) != 16:
          return None
      try:
          int(webid, 16)
      except TypeError:
          return None
      except ValueError:
          return None
      l = list(webid)
      for nybbleid in range(7, -1, -1):
          a, b = _swapat(key, nybbleid)
          _swap(l, b, a)
      i = int(''.join(l), 16)
      return i ^ key
docs: Takes a webid (a 16-character str suitable for including in URLs) and a key
      (an int, a private key for decoding it) and produces a storeID.