使用除 Python 之外的 Try 的多用戶輸入

Question

我的任務是創建一個 python 程序，該程序將要求用戶輸入並計算每月的貸款還款額，這是我必須解決的公式：公式。 這樣做並不難，但是作為獎勵，導師要求嘗試使用戶輸入“牢不可破”，這意味着如果輸入了預期之外的任何值，它不會破壞程序。 我認為這可以通過 Try except 輕松完成，這就是我所做的，但是我相信我的代碼可以以更簡潔的方式編寫，而不是對每個輸入進行 Try except 如下：

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") 

我覺得好像用戶輸入可以放入 For 循環，或者所有這些都放入一個 Try except 塊中？ 考慮之后，我將所有輸入放入一個 Try except 塊中，但是一旦您未能正確輸入用戶輸入的預期數據，它就會回到開頭，而不是您所提出的問題。 這不是我想要的。 看一看：

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")

您認為我如何修改此代碼以使其更簡潔、更短、更高效，而無需對每個用戶輸入進行 Try except？

Answer 1

對其進行模塊化，並使用一個通用函數來處理輸入和循環，直到用戶輸入所要求的內容。

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-string 非常好和優雅 - 只需將值或計算插入花括號內。 根據評論中的建議，您可能希望使用如圖所示的舍入函數或格式選項顯示兩位小數。

命名變量的更pythonic方法是

• 數量而不是 A
• 率而不是 R
• num_years 而不是 N 等等。

Answer 2

使用所有相關輸入提取函數中的重復過程。
我在最終輸出中添加了一些格式以避免小數點過多

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))