While循环else分支无限打印问题求助

嘿，我一眼就瞅出问题出在哪啦！咱们来捋一捋：

你的代码逻辑里，当用户输入的位置已经被占用（触发else分支）时，没有让用户重新输入新的位置。这就导致user_input一直停留在那个已经被占用的数值上——下次循环时，内层的合法性检查循环（判断输入是否是1-9）会直接跳过（因为数值本身是合法的），然后再次检查board[block]，发现还是被占用，于是又打印提示，就这样无限循环下去了。

修复方案一：把输入放到外层循环里 #

最简洁的方式是把获取输入的代码移到外层while循环内部，这样每次循环都会重新获取用户输入，从根源上避免重复使用旧值：

board = ["-","-","-","-","-","-","-","-","-"]
i = False
while not i:
    user_input = input("Enter position: ")
    # 检查输入是否合法
    while user_input not in ["1","2","3","4","5","6","7","8","9"]:
        user_input = input("Enter position: ")
    block = int(user_input) - 1
    if board[block] == "-":
        i = True
    else:
        print("Position not available, try again")

修复方案二：在else分支里重新获取输入 #

如果你不想调整输入的位置，也可以在else分支里主动让用户输入新值，更新user_input：

board = ["-","-","-","-","-","-","-","-","-"]
i = False
user_input = input("Enter position: ")
while not i:
    while user_input not in ["1","2","3","4","5","6","7","8","9"]:
        user_input = input("Enter position: ")
    block = int(user_input) - 1
    if board[block] == "-":
        i = True
    else:
        print("Position not available, try again")
        # 这里添加重新输入，更新user_input
        user_input = input("Enter position: ")

两种方案都能解决无限打印的问题，推荐第一种，逻辑更清晰，也避免了重复写input代码~

内容的提问来源于stack exchange，提问作者Sachin sharma