嵌套的while循环- Python

Question

我正在开发一个简单的转换程序，但我遇到了阻止用户键入需要整数的字符串的问题：

    choicecheck = 1 
    inputcheck = 1 
    while choicecheck == 1: 
        choice = input ("""please choose type of convert:
        1. Centimeters to inches
        2. Inches to centimeters
        3. Exit""") 


        while inputcheck == 1:
            if choice == "1":
                cm = int(input ("Please type in value in centimeters.")) 
                if type(cm) == int:
                    cmsum = cm * 0.39 # multiplies user input by 0.39
                    print (cm, " centimeters is ", cmsum, " inches") 
                    choicecheck = 0
                    inputcheck = 0
                else:
                     print("Sorry, invalid input")

当涉及到inputcheck时，if语句的else部分无法工作，我不知道原因。请帮帮忙。

Answer 1

while True:
    try:
        choice = int(input('please choose type of convert'))
    except ValueError:
        # user entered an input that couldn't be converted to int
        continue
    else:
        if not 1 <= choice <= 3:
            # valid int, invalid choice
            continue
        # success. stop looping
        break

现在，您有了一个表示它们的输入的int。它将继续询问，直到他们成功输入int

Answer 2

这将保持程序循环，直到用户选择退出。我使用了一个浮点数作为第二个用户输入，因为用户可能需要找到2.5英寸或类似的值。

while True:
    try:
        choice = int(input("""please choose type of convert:
        1. Centimeters to inches
        2. Inches to centimeters
        3. Exit"""))

        if choice == 1:
            while True:
                 try:
                    cm = float(input ("Please type in value in centimeters.")) 
                    cmsum = cm * 0.39 # multiplies user input by 0.39
                    print (cm, " centimeters is ", cmsum, " inches")
                    break
                 except ValueError:
                    print('error')

        elif choice ==2:
            while True:
                try:
                    stuff()
                    break
                except ValueError:
                    print('error')

        elif choice == 3:
            print('Thanks!')
            break

    except ValueError:
        print('error')