Question

您好我正在学习python，我正在尝试制作一个将钱转换成美元，欧元或英镑的小程序。有人可以帮助我，告诉我为什么不工作？感谢!!!

def calculate():
    currency_input = input("Insert value:")
    dollar = 34
    euro = 36
    pound = 52
    select_currency = input("Insert currency(dollar,euro or pound):")   
    if select_currency is "dollar":
        currency_input  * dollar
    elif select_currency is "euro":
        currency_input * euro
    elif select_currency is "pound":
        currency_input * pound
    else:
        print ("Please select a currency(dollar,euro,pound)!")
    calculate()
calculate()

Answer 1

您正在测试身份，而不是平等。请改用==：

if select_currency == "dollar":

is测试名称select_currency是否指的是同一个对象;两个对象可以是不同的但仍然具有相同的值，您可以使用==来测试它。

您需要修复所有字符串测试，并实际存储计算结果：

if select_currency == "dollar":
    result = currency_input  * dollar
elif select_currency == "euro":
    result = currency_input * euro
elif select_currency == "pound":
    result = currency_input * pound

更容易在这里使用字典：

currencies = {
    'dollar': 34,
    'euro': 36,
    'pound': 52,
}
if select_currency in currencies:
    result = currency_input * currencies[select_currency]
else:
    print ("Please select a currency(dollar,euro,pound)!")

Answer 2

您应该使用==而不是is，因为在这种情况下，is将无法执行您认为的操作。更多关于here。

使用.lower()允许用户也输入Dollars并仍然成功。

您似乎希望能够在用户输入无效信息时进行处理。您应该使用try except块来确保用户只输入currency_input

的数字

使用while True循环继续询问用户输入是否正确。如果他们输入了正确的输入，我们就会停止询问break语句。

字典可以轻松存储货币名称及其相关值。

对于所有货币，数学运算也是相同的，唯一改变的是货币的价值（美元，欧元......），所以我们可以查看用户选择的内容，然后乘以currency_input

def calculate():
    # we only want the user to input numbers
    while True:
        try:
            currency_input = float(input('Insert value: '))  # input always returns a str, we need to type cast
            break  # if input is valid we break out of the loop and move on
        except TypeError:  # handle the error when the input is not a number
            print('Please enter a number.')

    # use a dictionary because it is easier to read
    currency_dict = {
        'dollar': 34,
        'euro': 36,
        'pound': 52}

    # get the type of currency and do the math
    while True:
        select_currency = input('Insert currency(dollar,euro or pound): ').lower()
        if select_currency not in currency_dict:  # if the users enter something that is not in the dict
            print('Invalid currency')  # oops, try again
        else:
            money = currency_input * currency_dict[select_currency]  # we do the math
            return money  # return allows us to further manipulate that variable if we so desire 

print(calculate())

感谢Martijn Pieters指出了两项改进。

Python程序无法正常工作，输入==字符串无效

2 个答案: