shiritori.py

def game():
    """Play a single game, interactively"""

    last = None  # last word entered by player
    seen = set()  # all the words player tried so far

    while True:
        guess = input("Please type a word: ")

        if not guess:
            raise Exception("That's not fair!")
        if guess not in words:
            raise Exception("That's not a dictionary word!")
        if guess in seen:
            raise Exception("That word has been used already!")
        if last and guess[0] != last[-1]:
            raise Exception("The word should have started with %r" % last[-1])

        seen.add(guess)
        last = guess


if __name__ == "__main__":
    words = set(line.strip().lower()               # remove line terminators; accept proper nouns
                for line in open("word_list.txt")  # read file line by line; each line is a word
                if len(line.strip()) > 1)          # 1-letter words are not valid
    try:
        game()
    except Exception as e:
        print(e)