Try-Except ErrorCatching

Question

我试图强制用户在 python 中使用 try-except 输入一个数字，但它似乎没有效果。

while count>0:
    count=count - 1
    while (length != 8):
        GTIN=input("Please enter a product code ")
        length= len(str(GTIN))
        if length!= 8:
            print("That is not an eight digit number")
            count=count + 1
         while valid == False:
            try:
                GTIN/5
                valid = True
            except ValueError:
                 print("That is an invalid number")
                 count=count + 1

Answer 1

实际上，如果用户输入例如一个字符串，"hello"/5 会产生一个TypeError，而不是ValueError，所以请抓住它

Answer 2

您可以尝试将输入值设为 int int(value)，如果无法转换，则会引发 ValueError。

这里有一个函数可以用一些 cmets 做你想做的事情：

def get_product_code():
    value = ""
    while True:  # this will be escaped by the return
        # get input from user and strip any extra whitespace: " input  "
        value = raw_input("Please enter a product code ").strip()
        #if not value:            # escape from input if nothing is entered
        #    return None
        try:
            int(value)           # test if value is a number
        except ValueError:       # raised if cannot convert to an int
            print("Input value is not a number")
            value = ""
        else:                    # an Exception was not raised
            if len(value) == 8:  # looks like a valid product code!
                return value
            else:
                print("Input is not an eight digit number")

一旦定义，调用函数以获取用户的输入

product_code = get_product_code()

您还应该确保在您期待用户输入的任何时候排除和处理KeyboardInterrupt，因为他们可能会输入^C 或其他内容以使您的程序崩溃。

product code = None  # prevent reference before assignment bugs
try:
    product_code = get_product_code()  # get code from the user
except KeyboardInterrupt:  # catch user attempts to quit
    print("^C\nInterrupted by user")

if product_code:
    pass  # do whatever you want with your product code
else:
    print("no product code available!")
    # perhaps exit here