当变量值不匹配时如何停止python运行某些'if'代码

Question

尝试在python 2.7中创建决策菜单。

无法获得个性化且顺序混乱的选项。

除了if语法错误

pc =磅换算

kc =千克换算

cont = 1
while cont == 1:

    if input("Would you like to convert to pounds or kilograms?") == 'pounds':
        pc = 1

    if pc == 1:
        kilograms = float(input("Enter the amount of kilograms:  "))
        pounds = kilograms / 2.205

        print('The amount of pounds you entered is ', kilograms,
                  ' This is ', pounds, ' pounds ')
        pc = 0
        if input('Do you want to go again? (y/n) ') == 'n':
            cont = 0

    if input("Would you like to convert to pounds or kilograms?") == "kilograms":
        kc = 1

    if kc == 1:
        pounds = float(input("Enter the amount of pounds:  "))
        kilograms = pounds * 2.2
        grams = kilograms * 1000

        print('The amount of pounds you entered is ', pounds,
                  ' This is ', kilograms, ' kilograms ', 'and', grams,
                  'grams' )
        kc = 0

    if input('Do you want to go again? (y/n) ') == 'n':
        cont = 0

当第一个提示给出“未定义pc”时，以kilograms输入

如果您先输入pounds ，然后输入kilograms ，则该程序只能正确运行

Answer 1

您的代码中有一个“错误”。

仅当第一个提示== 'pounds'时才定义变量pc 。 因此，您得到的错误消息pc is not defined在第7行中pc is not defined ，因为只有在键入“磅”时才定义该错误消息。

Answer 2

while True: #generic while statement, only way to exit is break
    choice = input("Would you like to convert to pounds or kilograms: ") #store our choice in a variable for later
    if choice == 'pounds':
        kilograms = float(input("Enter the amount of kilograms:  "))
        pounds = kilograms / 2.205
        print('The amount of killograms you entered is ', kilograms,
                  ' This is ', pounds, ' pounds ')

    elif choice == "kilograms": #use an elif and define a different specific statement
        pounds = float(input("Enter the amount of pounds:  "))
        kilograms = pounds * 2.2
        grams = kilograms * 1000

        print('The amount of pounds you entered is ', pounds,
                  ' This is ', kilograms, ' kilograms ', 'and', grams,
                  'grams' )

    elif choice == "quit":
        print("Goodbye!")
        break #use break to break out of a loop

    else: #use an else to define a generic statement
        print "%s is not a valid choice"%choice
        continue #use continue to return to the beginning of the loop without doing anything after

    do_continue = input('Do you want to go again? (y/n) ')
    if do_continue == 'y':
        pass #do nothing and continue

    elif do_continue == 'n':
        print("Goodbye!")
        break

    else:
        print("What language is that? We will go again anyways!")