Question

我要做的是询问用户两个输入，如果其中一个输入小于零，或者输入是某个字符串，则再次询问输入。唯一有效的输入是数字＆gt; = 0。因此，您不能使用-1或cat作为输入。

尝试1：

number_of_books = input("What is the number of books in the game?: ")
number_of_chairs = input("What is the number of chairs in the game?: ")
while int(number_of_books) < 0 or int(number_of_chairs) < 0 or isinstance(number_of_books, str) or isinstance(number_of_chairs, str):
    print("Input cannot be less than 0 or cannot be some string.")
    number_of_books = input("What is the number of books in the game?: ")
    number_of_chairs = input("What is the number of chairs in the game?: ")

但是由此我意识到输入总是字符串，因此它会再次请求输入。

尝试2：

number_of_books = int(input("What is the number of books in the game?: "))
number_of_chairs = int(input("What is the number of chairs in the game?: "))
while number_of_books < 0 or number_of_chairs < 0 or isinstance(number_of_books, str) or isinstance(number_of_chairs, str):
    print("Input cannot be less than 0 or cannot be some string.")
    number_of_books = int(input("What is the number of books in the game?: "))
    number_of_chairs = int(input("What is the number of chairs in the game?: "))

但是有了这个，我意识到你不能做int（'some string'）

所以我想知道是否有办法做到这一点，或者这是不可能的事情？

Answer 1

您应该为每个输入使用while循环，因此只会再次询问无效循环。通过使用while True，您需要输入一次，并在它有效时中断。尝试转换为int，如果无法完成，则会ValueError。异常导致打印自定义错误，并重新启动循环。

while True:
    books_input = input("What is the number of books in the game?: ")
    try:
        number_of_books = int(books_input)
        if number_of_books < 0:
            raise ValueError
    except ValueError:
        print('Input must be an integer and cannot be less than zero')
    else:
        break

你需要为每个输入执行此操作（可能有两个以上？），因此创建一个函数来完成繁重工作是有意义的。

def non_negative_input(message):
    while True:
        input_string = input(message)
        try:
            input_int = int(books_input)
            if input_int < 0:
                raise ValueError
        except ValueError:
            print('Input must be an integer and cannot be less than zero')
        else:
            break
    return input_int

致电：

non_negative_input("What is the number of books in the game?: ")

Answer 2

解决方案是强制解决int（）并捕获任何异常，例如：

while True:
    try:
        number_of_books = int(raw_input('Enter number of books:'))
        if number_of_books < 0:
            raise ValueError('must be greater than zero')
    except ValueError, exc:
        print("ERROR: %s" % str(exc))
        continue
    break

可能你应该将它放在一个函数中，并将提示符设为变量（以允许重复使用）。

Answer 3

使用try except方法

while stringval = input("What is the number you want to enter"):
  try:
    intval = int(stringval)
    if intval > -1:
      break
  except ValueError:
    print 'Invalid answer, try again'

# Process intval now

整数作为唯一有效的输入

3 个答案: