传入字符串时出现 UnboundLocalError

Question

我是 python 新手，我想练习一下，try/except但我卡住了：

def monitor():

    try:

        brightness = int(input("brightness:"))

    except ValueError:

        print("please pass in a number")

    if brightness < -1 or brightness > 101:

        print("invaild",brightness)

    else:

        print("invalid",brightness)

while True:

    monitor()

我希望输入字符串时不会出现错误，但它给了我：

UnboundLocalError

Answer 1

检查此代码片段try:&nbsp; &nbsp; brightness = int(input("brightness:"))except ValueError:&nbsp; &nbsp; print("please pass in a number")print(brightness)print(brightness)如果在被要求输入时输入“有点暗” ，应该输出什么？因为输入不是整数，int()这种情况下会抛出异常，所以局部变量brightness不会被初始化。您可以在except子句中将其初始化为某个默认值，但在这种情况下，如果输入不正确，您可能不应该对 brightess 值做任何事情。你可以在 try...except 中移动逻辑处理brightness，那么它只有在输入可以被解析的情况下才会执行。def monitor():&nbsp; &nbsp; try:&nbsp; &nbsp; &nbsp; &nbsp; brightness = int(input("brightness:"))&nbsp; &nbsp; &nbsp; &nbsp; if brightness < -1 or brightness > 101:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invaild",brightness)&nbsp; &nbsp; &nbsp; &nbsp; else:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invalid",brightness)&nbsp; &nbsp; except ValueError:&nbsp; &nbsp; &nbsp; &nbsp; print("please pass in a number")

Answer 2

改用它（这可以解决您提出的问题）：def monitor():&nbsp; &nbsp; while True:&nbsp; &nbsp; &nbsp; &nbsp; try:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; brightness = int(input("brightness:"))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if brightness < -1 or brightness > 101:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invaild",brightness)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if brightness < -1 or brightness > 101:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invaild",brightness)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; else:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invalid",brightness)&nbsp; &nbsp; &nbsp; &nbsp; except ValueError:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("please pass in a number")&nbsp; &nbsp; &nbsp; &nbsp; else:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print("invalid",brightness)monitor()您的代码也有逻辑错误，因为无论输入（亮度），输出总是print("invalid",brightness)如果您不知道，请告诉您，以防万一。您的代码输出：我的输出：

Answer 3

请检查这个，这里我们强制用户只输入整数值。&nbsp; &nbsp; brightness=-2while (brightness < -1 or brightness > 101):&nbsp; &nbsp; try:&nbsp; &nbsp; &nbsp; &nbsp; brightness = int(input("brightness:"))&nbsp; &nbsp; except ValueError:&nbsp; &nbsp; &nbsp; &nbsp; print("please pass in a number")if brightness < -1 or brightness > 101:&nbsp; &nbsp;print("invaild",brightness)else:&nbsp; &nbsp;print("Valid",brightness)