optimised chainer

counter = 0
key = ""
masterkey = ""
while True:
  for word in file.readline().strip().split(" "):
    counter = counter +1
    if counter == 1:
      key = word
    elif counter < chainlen:
      key = key + " " + word
    elif counter == chainlen:
      key = key + " " + word
      masterkey = key
    else: # counter exceeded
      # put code here to read in chaintable (optimised, but code size increased)
  if counter >= chainlen:
    break