python - KeyErrors 以及如何引发 KeyError

Question

对于我的家庭作业，如果用户输入的键(文本)包含任何非字母字符并重新提示，我被告知要引发一个键错误。到目前为止，我有这个似乎有效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 KeyError 的正确用法(它应该用于 dict 查找或类似情况)，但如果这是你被要求做的然后尝试这样的事情:

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