不确定python函数

Question

I am only starting and getting mad over this function (it gives me the wrong outputs):

def rental_car_cost(days):
    x = 40
    if days < 2:
        return days*x
    elif days >= 3:
        return days*x-20
    elif days>= 7:
        return days*x-50
    else:
        print "Please enter nr of days"

Also, how do I make sure that a number is entered for "days"?

Answer 1

Not sure what you are expecting, however change the order of the elif conditions:

def rental_car_cost(days):
    if isinstance(days, int):
        x = 40
        if days < 2:
            return days*x
        elif days >= 7:
            return days*x-50
        elif days>= 3:
            return days*x-20
    else:
        print "Please enter nr of days"

Answer 2

The days>= 7 and else clauses never trigger, because the earlier days >= 3 triggers on the same inputs. if / elif / else clauses are processed in order until one of them is triggered.

What you need are clauses for days < 2 , days < 7 and else .

To detect non-numbers, start with

if not isinstance(days, int):

which does a type check for integers.

Answer 3

rental_car_cost(2) should equal 60

But, none of your if statements will match 2. 2 isn't less than 2, nor is it greater than or equal to 3, nor is it greater than or equal to 7. Follow the advise from the other two answers by larsmans and Ankit Jaiswal also, but I'm assuming 2 should match the days*x-20 part. Just change elif days >= 3: to elif days >= 2: .