python请求用户输入有效参数

原创 CodeDeveloper 程序熵 2023-05-21 17:53

问：

我正在编写一个接受用户输入的程序。

#note: Python 2.7 users should use `raw_input`, the equivalent of 3.X's `input`age = int(input("Please enter your age: "))if age >= 18:     print("You are able to vote in the United States!")else:    print("You are not able to vote in the United States.")

只要用户输入有意义的数据，程序就会按预期工作。

Please enter your age: 23You are able to vote in the United States!

但是，如果用户输入无效数据就会失败：

Please enter your age: dickety sixTraceback (most recent call last):  File "canyouvote.py", line 1, in <module>    age = int(input("Please enter your age: "))ValueError: invalid literal for int() with base 10: 'dickety six'

我希望程序再次请求输入，而不是崩溃。像这样：

Please enter your age: dickety sixSorry, I didn't understand that.Please enter your age: 26You are able to vote in the United States!

如何请求有效输入而不是崩溃或接受无效值（例如-1）？

答：

题主的描述表明在输入无效数据时，程序抛出了异常，为了应对异常而不让程序崩溃，我们可以使用前文 Python 控制流之 try-except和finally语句写过的 try-except 语句。示例代码如下：

while True:    try:        age = int(input("Please enter your age: "))    except ValueError:        print("Sorry, I didn't understand that.")        continue    else:        #inut data is valid.        #now, we can exit the loop.        breakif age >= 18:    print("You are able to vote in the United States!")else:    print("You are not able to vote in the United States.")

进一步，要想使代码更简洁，可以采用 Python 库 click。

Click 是一个利用很少的代码以可组合的方式创造优雅命令行工具接口的 Python 库。它致力于将创建命令行工具的过程变的快速而有趣。我们可以编写如下代码实现题主的需求：

import click
age = click.prompt('Please enter your age', type=int)if age >= 18:    print("You are able to vote in the United States!")else:    print("You are not able to vote in the United States.")

参考：

stackoverflow question 23294658
https://click.palletsprojects.com/en/8.1.x/prompts/#input-prompts

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