python - 无法弄清楚为什么我收到 UnboundLocalError

Question

我正在尝试将代码“排除”为 int 的字符串。 - “长度”。当我输入 except ValueError 时，我返回“请输入数字”，但添加了更多错误。我还添加了 except UnboundLocalError ，但这似乎不起作用。请让我知道我做错了什么!这是我的代码:

import random
import string


def RPG():
    try:
        RPG = ""
        count = 0
        length = int(
            input("How many characters would you like in your password? "))
    except (ValueError, UnboundLocalError):
        print("Please enter a number.")
    while count != length:
        upper = [random.choice(string.ascii_uppercase)]
        lower = [random.choice(string.ascii_lowercase)]
        num = [random.choice(string.digits)]
        symbol = [random.choice(string.punctuation)]
        everything = upper + lower + num + symbol
        RPG += random.choice(everything)
        count += 1
        continue
    if count == length:
        print(RPG)
# could also use string.printable for digits, letters, punct., and whitespace.


RPG()

这是我使用此代码并在 length 中输入字符串而不是整数得到的结果:

How many characters would you like in your password? j
Please enter a number.
Traceback (most recent call last):
  File "c:\Users\jkelly\Desktop\python\code.py", line 28, in <module>
    pwd()
  File "c:\Users\jkelly\Desktop\python\code.py", line 14, in pwd
    while count != length:
UnboundLocalError: local variable 'length' referenced before assignment

我只期望“请输入数字”，而不是其余的错误，任何帮助将不胜感激。感谢您的宝贵时间!

Answer 1

原始代码的问题是，尽管 count != length 总是被执行，无论 try- except 部分如何。如果未引发 ValueError 或 UnboundLocalError，则可以通过仅继续进行 while 循环来避免这种情况。通过在 try-except 之前初始化 c=1 并仅在 try 部分将其更改为 0，如果没有发生异常，程序只会进入 while 循环。

import random
import string


def RPG():
    c=0
    try:
        RPG = ""
        count = 0
        length = int(
            input("How many characters would you like in your password? "))
    except (ValueError, UnboundLocalError):
        print("Please enter a number.")
        c=1
    if c==0:
        while count != length:
            upper = [random.choice(string.ascii_uppercase)]
            lower = [random.choice(string.ascii_lowercase)]
            num = [random.choice(string.digits)]
            symbol = [random.choice(string.punctuation)]
            everything = upper + lower + num + symbol
            RPG += random.choice(everything)
            count += 1
            continue
        if count == length:
            print(RPG)
# could also use string.printable for digits, letters, punct., and whitespace.


RPG()