better to pickle a frozenset and use that.

  import pickle

  # initialize:
  wordset = frozenset(line.lower().rstrip() for line in open('/usr/share/dict/words'))
  pickle.dump(wordset, open('/tmp/wordset.pkl', 'wb', -1))

  # when you want to use it:
  wordset = pickle.load(open('/tmp/wordset.pkl', 'rb'))

  'bear' in wordset # == True