键错误和如何提升键

Question

对于我的家庭作业，我被告知，如果用户输入的密钥（文本）包含任何非字母字符和重新提示，则会引发密钥错误。到目前为止，我已经有了这个似乎可以工作，但显然没有使用预期的try/except结构

key=input("Please enter the key word you want to use: ")
ok=key.isalpha()
while (ok==False):
    print("The key you entered is invalid. Please try again")
    key=input("Please enter the key word you want to use")

Answer 1

这不是KeyError（应该用于dict查找或类似情况）的适当用法，但如果要求您这样做，请尝试以下操作：

def prompt_thing():
    s = raw_input("Please enter the key word you want to use: ")
    if s == '' or not s.isalnum():
        print("The key you entered is invalid. Please try again")
        raise KeyError('non-alphanumeric character in input')
    return s

s = None
while s is None:
    try:
        s = prompt_thing()
    except KeyError:
        pass