无法弄清楚为什么我会收到 UnboundLocalError

Question

我试图让代码“排除”一个 int 的字符串。 - “长度”。当我输入除 ValueError 之外的内容时，我返回“请输入一个数字”，但添加了更多错误。我还添加了除了 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长度中输入字符串而不是整数后得到的结果：

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

我只希望“请输入一个数字”，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

原始代码的问题在于count != length 总是被执行，而不管try-except 部分。如果没有引发ValueError 或UnboundLocalError，则仅继续执行while 循环可以避免这种情况。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，程序只会继续进行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()

Answer 2

如果您导致错误，程序的其余部分仍将执行。您需要重复输入，直到获得正确的输入。

import random
import string


def RPG():
    while True:
        try:
            RPG = ""
            count = 0
            length = int(
                input("How many characters would you like in your password? "))
            break
        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()