未定义变量 — Python — 条件语句

Question

So I'm having issues with this code. When I run it it states that the variable cost_of_rental is not defined. What is it I'm doing wrong?

Here is my code:

type_car = input("Welcome to CarRental. What type of car would you like to rent?  ")

rent_duration = int(input("For how many days do you wish to rent this car?  "))

available_classes = ['Class B', 'Class C', 'Class D']

if type_car == 'Class B':
    if rent_duration <= 6:
        cost_of_rental = 27 * rent_duration

    elif rent_duration <= 27:
        cost_of_rental = 167 + (rent_duration-7)*25

    elif rent_duration <= 60:
        cost_of_rental = 662 + (rent_duration-28)*23

if type_car == 'Class C': 
    if rent_duration <= 6: 
        cost_of_rental = 34*rent_duration

    elif rent_duration <= 27:  
        cost_of_rental = 204 + (rent_duration - 7)*31

    elif rent_duration <= 60:
        cost_of_rental = 810 + (rent_duration - 28)*28

if type_car == 'Class D':
    if rent_duration <= 6: 
        print("Sorry, Class D cars cannot be rented for less than 7 days.")

    elif rent_duration <= 27: 
        cost_of_rental = 810 + (rent_duration-28)*43

    elif rent_duration <= 60:
        cost_of_rental = 1136 + (rent_duration - 28)*38


print("Your total cost is:  ", cost_of_rental)

Answer 1

As comments to your question suggest you should declare cost_of_rental variable beside you conditions. Currently if none of your condition is True than your cost_of_rental variable is not defined. In another words - you define it only if you satisfy any of your conditions. Adding cost_of_rental = 0 on the beginning or else (not elif ) statements to your conditions should solve your issue.

Answer 2

Since your if / elif structure has no else block, there are paths through your code which do not assign a value to the variable cost_of_rental . If these paths should never be taken by a valid rent_duration , I would recommend dealing with it by raising a ValueError to indicate that rent_duration is invalid.

Note that the same applies to your outer if statements - if type_car isn't one of the options you've checked for, I assume this means the input is invalid, so raising a ValueError is appropriate. Raising an error means your code won't continue as normal, so the print statement at the bottom won't be reached (which is what you want when the input is invalid).

If you want to print a friendly error message to the user instead, use try / catch . Generally, it is not a good idea to just print the error message, because your code will continue executing with the invalid data, which usually means you'll get a result that doesn't make sense (eg printing the error message and then still printing a total cost afterwards).

type_car = input("Welcome to CarRental. What type of car would you like to rent?  ")

rent_duration = int(input("For how many days do you wish to rent this car?  "))

available_classes = ['Class B', 'Class C', 'Class D']

if type_car == 'Class B':
    if rent_duration <= 6:
        cost_of_rental = 27 * rent_duration

    elif rent_duration <= 27:
        cost_of_rental = 167 + (rent_duration-7)*25

    elif rent_duration <= 60:
        cost_of_rental = 662 + (rent_duration-28)*23

    else:
        raise ValueError('Invalid rent duration')

elif type_car == 'Class C': 
    if rent_duration <= 6: 
        cost_of_rental = 34*rent_duration

    elif rent_duration <= 27:  
        cost_of_rental = 204 + (rent_duration - 7)*31

    elif rent_duration <= 60:
        cost_of_rental = 810 + (rent_duration - 28)*28

    else:
        raise ValueError('Invalid rent duration')


elif type_car == 'Class D':
    if rent_duration <= 6: 
        raise ValueError("Sorry, Class D cars cannot be rented for less than 7 days.")

    elif rent_duration <= 27: 
        cost_of_rental = 810 + (rent_duration-28)*43

    elif rent_duration <= 60:
        cost_of_rental = 1136 + (rent_duration - 28)*38

    else:
        raise ValueError('Invalid rent duration')

else:
    raise ValueError('Invalid car type')


print("Your total cost is:  ", cost_of_rental)