如何创建“while”异常循环？答案

【问题标题】：How can I create a 'while'-exception loop?如何创建“while”异常循环？
【发布时间】：2018-12-01 21:39:58
【问题描述】：

我正在处理一个需要用户输入的小型编码挑战。应检查此输入是否为数字。我创建了一个“try: ... except ValueError: ...”块，它检查一次输入是否为数字，但不是多次。我希望它基本上可以连续检查。

可以创建一个while异常循环吗？

我的代码如下：

try:
    uinput = int(input("Please enter a number: "))

    while uinput <= 0:
        uinput = int(input("Number is negative. Please try again: "))
    else:
        for i in range(2, uinput):
            if (uinput % i == 0):
                print("Your number is a composite number with more than
                       one divisors other than itself and one.")
                break
            else:
                print(uinput, "is a prime number!")
                break

except ValueError:
    uinput = int(input("You entered not a digit. Please try again: "))

【问题讨论】：

标签： python python-3.x while-loop exception-handling

【解决方案1】：

flag = True
while flag:
    try:
        uinput = int(input("Please enter a number: "))

        while uinput <= 0:
            uinput = int(input("Number is negative. Please try again: "))
        else:
            flag=False
            for i in range(2, uinput):
                if (uinput % i == 0):
                    print("Your number is a composite number with more than one divisors other than itself and one.")
                    break
                else:
                    print(uinput, "is a prime number!")
                    break

    except ValueError:
        print('Wrong input')

输出：

(python37) C:\Users\Documents>py test.py
Please enter a number: qwqe
Wrong input
Please enter a number: -123
Number is negative. Please try again: 123
123 is a prime number!

我添加标志 boolean 以使其即使输入正确并删除输入也不会重复，除非它会询问 2 次。

【讨论】：

非常感谢您的回答。它解决了我的问题！ :)

【解决方案2】：

如果你只按 Enter，循环就会终止：

while True:

    uinput = input("Please enter a number: ")
    if uinput.strip()=="":
        break
    try:
        uinput=int(uinput)    
    except:
        print("You entered not a digit. Please try again")
        continue

    if uinput<=0:
        print("Not a positive number. Please try again")
        continue

    for i in range(2, uinput):
            pass; # put your code here

【讨论】：