验证浮点数据类型python

Question

我正在为我的最终项目用 Python 编写一个简单的计算器，但在验证用户输入的值是浮点数据类型时遇到问题。我想这样做，如果值是字符串类型，它会打印“值必须是整数或小数 - 请输入有效数字”，然后将其循环回要求用户输入，直到用户给出有效入场。我试过了，但我被卡住了。所以这是我到目前为止的代码：

keepProgramRunning = True

print ("Welcome to the Calculator Application!")
good = True
while keepProgramRunning:

    print ("1: Addition")

    print ("2: Subtraction")

    print ("3: Multiplication")

    print ("4: Division")

    print ("5: Quit Application")


    choice = input("Please choose what you would like to do: ")

    if choice == "1":
        n1 = float(input ("Enter your first number: "))
        n2 = float(input ("Enter your second number: "))
        print ("Your result is: ", n1 + n2)
    elif choice == "2":
        n1 = float(input ("Enter your first number: "))
        n2 = float(input ("Enter your second number: "))
        print ("Your result is: ", n1 - n2)
    elif choice == "3":
        n1 = float(input ("Enter your first number: "))
        n2 = float(input ("Enter your second number: "))
        print ("Your result is: ", n1 * n2)
    elif choice == "4":
        n1 = float(input ("Enter your first number: "))
        n2 = float(input ("Enter your second number: "))
        try:
            print ("Your result is: ", n1 / n2)
        except:
            if n2 == 0:
                print ("Zero Division Error - Enter Valid Number")
                while good:
                    n2 = float(input ("Enter your second number: "))
                    if n2!=0:
                        good =False
                        print ("Your result is: ", n1 / n2)
    elif choice == "5":
        print ("Thank you for using the calculator. Goodbye!")
        keepProgramRunning = False
    else:
        print ("Please choose a valid option.")

Answer 1

假设您在这里使用 Python 3.x，以下每一行：

n1 = float(input ("Enter your first number: "))

...ValueError如果给定一些无法转换为浮点数的东西，则会引发一个。

因此，与其验证然后转换，不如尝试转换，让转换器成为它自己的验证器。

例如，而不是这样：

n1 = float(input ("Enter your first number: "))
n2 = float(input ("Enter your second number: "))
print ("Your result is: ", n1 + n2)

… 你可以这样做：

while True:
    try:
        n1 = float(input ("Enter your first number: "))
        n2 = float(input ("Enter your second number: "))
    except ValueError:
        print("When I ask for a number, give me a number. Come on!")
    else:
        print ("Your result is: ", n1 + n2)
        break

如果您想分别检查每个值，只需执行两个较小的循环try而不是一个大循环。

与其将这段代码复制粘贴 6 次，不如将其重构为一个函数。像这样的东西：

def get_two_floats():
    while True:
        try:
            n1 = float(input ("Enter your first number: "))
            n2 = float(input ("Enter your second number: "))
        except ValueError:
            print("When I ask for a number, give me a number. Come on!")
        else:
            return n1, n2

或者，如果您想分别验证每一个：

def get_float():
    while True:
        try:
            return float(input ("Enter your second number: "))
        except ValueError:
            print("When I ask for a number, give me a number. Come on!")

def get_two_floats();
    return get_float(), get_float()

然后你可以这样做：

if choice == "1":
    n1, n2 = get_two_floats()
    print ("Your result is: ", n1 + n2)
elif choice == "2":
    n1, n2 = get_two_floats()
    print ("Your result is: ", n1 - n2)
# etc.

附带说明：要捕获除以零，而不是处理所有异常，然后根据输入试图找出导致错误的原因，只需处理ZeroDivisionError. （一般来说，裸机except:是个坏主意，除非你打算使用sys.exc_info()、重新设计raise或类似的东西。使用except SpecificException:几乎总是更好。或者，更频繁地except SpecificException as e:，，所以你可以用 做一些事情e，喜欢print它在错误消息中。）