为何无法在函数中使用raw_input？Python代码类型错误排查

首先，咱们拆解下你遇到的两个核心问题：

1. 为什么会出现类型错误？ #

你看到的TypeError: unsupported operand type(s) for -=: 'str' and 'int'报错，根源很明确：raw_input()获取的所有输入都是字符串类型，但你的函数（比如rental_car_cost）需要整数来做算术运算。

举个例子：你输入的days是字符串，执行cost = days * 40时，Python会把字符串重复40次（比如输入"3"会变成一串"3"），后续的cost -= 50就会尝试用字符串减整数，这显然不符合运算规则，所以触发报错。

2. 为何“无法在函数中使用raw_input”？ #

其实**raw_input()完全可以在函数里使用**，你可能是碰到了这两种情况：

• 如果你用的是Python 3：raw_input()已经被重命名为input()了，这时候写raw_input会报NameError，让你误以为不能用；
• 你的代码里raw_input是写在全局作用域，不是函数内，但这不代表函数里不能用——比如你可以把输入逻辑直接整合到trip_cost函数里，示例如下：

def trip_cost():
    city = raw_input("Which city will you stay in ")
    days = int(raw_input("How long is the stay "))
    spending_money = int(raw_input("How much is your spending budget "))
    return rental_car_cost(days) + hotel_cost(days) + plane_ride_cost(city) + spending_money

trip_cost()

3. 修正你的代码 #

针对当前的报错，只需要把raw_input获取的数值类输入转换成整数即可，同时我帮你修正了拼写错误（你写的spening budget应该是spending budget）：

def hotel_cost(nights): 
    return 140 * nights 

def plane_ride_cost(city): 
    if city == "Charlotte": 
        return 183 
    elif city == "Tampa": 
        return 220 
    elif city == "Pittsburgh": 
        return 222 
    elif city == "Los Angeles": 
        return 475 

def rental_car_cost(days): 
    cost = days * 40 
    if days >= 7: 
        cost -= 50 
    elif days >= 3: 
        cost -= 20 
    return cost 

def trip_cost(city, days, spending_money): 
    return rental_car_cost(days) + hotel_cost(days) + plane_ride_cost(city) + spending_money 

city = raw_input("Which city will you stay in ")
# 将输入转换为整数类型
days = int(raw_input("How long is the stay "))
spending_money = int(raw_input("How much is your spending budget "))

print trip_cost(city, days, spending_money)

如果是Python 3环境，记得把所有raw_input()替换成input()，同时print要改成函数形式print(...)：

# Python 3适配版本
def hotel_cost(nights): 
    return 140 * nights 

def plane_ride_cost(city): 
    if city == "Charlotte": 
        return 183 
    elif city == "Tampa": 
        return 220 
    elif city == "Pittsburgh": 
        return 222 
    elif city == "Los Angeles": 
        return 475 

def rental_car_cost(days): 
    cost = days * 40 
    if days >= 7: 
        cost -= 50 
    elif days >= 3: 
        cost -= 20 
    return cost 

def trip_cost(city, days, spending_money): 
    return rental_car_cost(days) + hotel_cost(days) + plane_ride_cost(city) + spending_money 

city = input("Which city will you stay in ")
days = int(input("How long is the stay "))
spending_money = int(input("How much is your spending budget "))

print(trip_cost(city, days, spending_money))

内容的提问来源于stack exchange，提问作者Somil Varshney