Try循环引发KeyError

Question

[当我使用try/except时，会得到KeyError，但是当我不使用try时，它会按预期工作。我敢肯定这是一个简单的修复程序，但是到目前为止，我已经花了一个多小时来解决这个问题，感谢您的帮助。这是代码，请原谅简单！

def return_book():
    """Return a book to the library"""
    print("To return the book, you will need the ISBN")
    isbn = str(input("Please enter the book's ISBN: "))
    amount = input("How many books are you returning? ")

    try:
        isbn = int(isbn)
    except ValueError:
        print()
        input("That is not a number, press enter to try again ")
        return_book()

    try:
        amount = int(amount)
    except ValueError:
        print()
        input("That is not a number, press enter to try again ")
        return_book()

    library[isbn][2] = library[isbn][2] + int(amount)
    print(library)

Answer 1

当我们尝试从不存在的字典访问键时，发生了KeyError，您正在将字符串转换为整数并将该整数用作键！使用str（isbn）再次使isbn成为字符串：

try:
    isbn = int(isbn)
except ValueError:
    print()
    input("That is not a number, press enter to try again ")
    return_book()

try:
    amount = int(amount)
except ValueError:
    print()
    input("That is not a number, press enter to try again ")
    return_book()

library[str(isbn)][2] = library[str(isbn)][2] + int(amount)
print(library)