Try Except Python 的多用户输入

Question

我的任务是创建一个 python 程序，该程序将要求用户输入并计算每月的贷款还款额，这是我必须计算的公式：Formula。这样做并不太难，但是作为奖励，导师要求尝试让用户输入 'unbreakable'，这意味着如果输入了预期之外的任何值，它不会破坏程序。我认为这可以通过 Try Except 轻松完成，这就是我所做的，但是我相信我的代码可以以更简洁的方式编写，而不是对每个输入都使用 Try Except，如下所示：

err = "Please enter a number only!!"
while True:
    try:
        A = int(input("How much were you loaned? "))
    except ValueError:
        print(err)
        continue
    else:
        break
while True:
    try:
        R = float(input("At what monthly rate interest? ")) / 100
    except ValueError:
        print(err)
        continue
    else:
        break
while True:
    try:
        N = int(input("And how many years is the loan for? "))
    except ValueError:
        print(err)
        continue
    else:
        break
RA = R * A
RN = 1 - (1 + R) ** -N
P = RA / RN
print("You will pay £", P, "yearly", "or, £", P / 12, "monthly")

我觉得也许可以将用户输入放入一个 For 循环中，或者将所有这些放入一个 Try Except 块中？考虑之后，我将所有输入都放在一个 Try Except 块中，但是一旦您未能正确输入用户输入的预期数据，它就会直接回到开头，而不是您的问题。这不是我想要的。看看：

err = "Please enter a number only!!"
while True:
    try:
        A = int(input("How much were you loaned? "))
        R = float(input("At what monthly rate interest? ")) / 100
        N = int(input("And how many years is the loan for? "))
    except ValueError:
        print(err)
        continue
    else:
        break
RA = R * A
RN = 1 - (1 + R) ** -N
P = RA / RN
print("You will pay £", P, "yearly", "or, £", P / 12, "monthly")

您认为我可以如何修改这段代码，使其更简洁、更短、更高效，而无需对每个用户输入进行尝试？

Answer 1

使用所有相关输入提取函数中的重复过程。
我在最终输出中添加了一些格式以避免小数点太多

def get_value(message, func, denominator = 1):
   try_again = True
   v = None
   while try_again:
      try:
         v = func(input(message))/denominator
      except ValueError:
         print("Please enter a number only!!")
      else:
         try_again= False   
   return v

A = get_value("How much were you loaned? ", int)
R = get_value("At what monthly rate interest? ", float, denominator=100.0)
N = get_value("And how many years is the loan for? ", int)

RA = R * A
RN = 1 - (1 + R) ** -N
P = RA / RN
print("You will pay £ {:.2f} yearly or £ {:.2f} monthly".format(P, P / 12))

Answer 2

将其模块化，并使用处理输入和循环的通用函数，直到用户输入要求的内容。

def get_num(prompt="Enter number: "):
    """
    (str) -> num
    Outputs a prompt and loops until a valid number is
    entered by the user, at which point that value is
    returned and the function terminates
    """
    while True:
        num = input(prompt)
        try:
            num = float(num)
            return num
        except:
            print("Must enter a valid number")

def do_calc():
    """(None) -> None
    Get user input, perform calculations and output results
    """
    A = int(get_num("How much were you loaned? "))
    R = get_num("At what monthly rate interest? ") / 100
    N = int(get_num("And how many years is the loan for? "))
    RA = R * A
    RN = 1 - (1 + R) ** -N
    P = RA / RN
    print(f"You will pay £{round(P, 2)} yearly or £{P/12:.2f} monthly")

do_calc()

使用 Python 3 中的 f 字符串非常漂亮和优雅 - 只需将值或计算插入花括号内即可。根据评论中的建议，您可能希望使用所示的舍入函数或格式选项显示两位小数。

一种更符合 Python 风格的变量命名方式是

金额而不是 A
比率而不是 R
num_years 而不是 N 等等。

Try Except Python 的多用户输入

Multiple User Input with Try Except Python

python

user-input

try-except