Python中的Hangman :尝试在空格中显示猜测的字母时引发键入错误

import random

def hangman():
    word_list = ['apple', 'banana', 'orange', 'watermelon'] # 答案词汇列表
    answer = random.choice(word_list) # 从列表中随机选择一个答案
    guessed_letters = [] # 已猜测的字母列表
    wrong_letters = [] # 错误的猜测列表
    tries = 6 # 总共可以猜错的次数

    while tries > 0:
        # 显示当前的猜测进度
        display_word = ''
        for letter in answer:
            if letter in guessed_letters:
                display_word += letter
            else:
                display_word += '_'
        
        print(display_word)
        print(f"Wrong guesses: {wrong_letters}")
        print(f"Tries left: {tries}")

        # 获取用户输入
        guess = input("Guess a letter: ").lower()

        # 检查用户输入是否合法
        if len(guess) != 1 or not guess.isalpha():
            print("Please enter a single letter.")
            continue

        # 检查字母是否已经猜测过
        if guess in guessed_letters or guess in wrong_letters:
            print("You've already guessed that letter.")
            continue

        # 检查字母是否在答案中出现
        if guess in answer:
            guessed_letters.append(guess)
            print("Correct guess!")
        else:
            wrong_letters.append(guess)
            tries -= 1
            print("Wrong guess!")

        # 检查游戏是否结束
        if all(letter in guessed_letters for letter in answer):
            print("Congratulations! You won!")
            break

    if tries == 0:
        print("You lost! The word was: " + answer)

hangman()