为何输入exit()后Python代码陷入无限循环？

先贴出你的代码：

executed = False

while executed == False:
    try:
        inp = input("Enter the variable you want to change (e.g.: limit = 10): ")
        eval(inp, globals())
    except:
        print("Invalid input")
        continue
    print("Variable has been changed")
    executed = True

为什么输入exit()会触发无限循环？ #

当你输入exit()执行时，eval(inp, globals())会调用exit()函数——这个函数本质是抛出SystemExit异常，用来终止程序。

但你的代码用了裸except:（捕获所有异常），把SystemExit也拦下来了，程序没终止，反而执行print("Invalid input")后用continue回到循环开头。

更关键的是：exit()执行后，标准输入流（stdin）会被置为EOF（文件结束）状态。后续再调用input()时，因为没有任何输入可读，会直接抛出EOFError异常，而这个异常又被裸except:捕获，导致循环无限重复：每次跳过输入等待，直接打印"Invalid input"，周而复始。

解决办法 #

1. 只捕获特定异常

把裸except:改成捕获输入不合法的特定异常（比如语法错误、未定义变量），让SystemExit和EOFError正常终止程序：

executed = False

while executed == False:
    try:
        inp = input("Enter the variable you want to change (e.g.: limit = 10): ")
        eval(inp, globals())
    except (SyntaxError, NameError):  # 仅处理输入语法或变量不存在的异常
        print("Invalid input")
        continue
    print("Variable has been changed")
    executed = True

2. 单独处理exit命令

在执行eval前判断输入是否为exit()，直接终止程序：

executed = False

while executed == False:
    try:
        inp = input("Enter the variable you want to change (e.g.: limit = 10): ")
        if inp.strip() == "exit()":
            exit()
        eval(inp, globals())
    except:
        print("Invalid input")
        continue
    print("Variable has been changed")
    executed = True

3. 排除终止类异常

如果一定要用宽范围捕获，手动排除SystemExit和EOFError，让程序正常终止：

executed = False

while executed == False:
    try:
        inp = input("Enter the variable you want to change (e.g.: limit = 10): ")
        eval(inp, globals())
    except (SystemExit, EOFError):
        raise  # 重新抛出异常，让程序正常终止
    except:
        print("Invalid input")
        continue
    print("Variable has been changed")
    executed = True

内容的提问来源于stack exchange，提问作者Westec