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Python Object-Oriented Python Instant Objects Master Class

Posted by Caleb Newell
Caleb Newell
12,562 Points

race car

Vrroom!

OK, now let's add a method named run_lap. It'll take a length argument. It should reduce the fuel_remaining attribute by length multiplied by 0.125.

Oh, and add a laps attribute to the class, set to 0, and increment it each time the run_lap method is called.

racecar.py 
class RaceCar():    
    def __init__(self, color, fuel_remaining, laps=0, **kwargs):
        self.color = color
        self.laps = laps
        self.fuel_remaining = fuel_remaining

        for key, value in kwargs.items():
            setattr(self, key, value)

    def run_lap(self, length, **kwargs):
        self.fuel_remaining = (fuel_remaining - 0.125) * length
        laps = laps + 1

4 Answers

Unsubscribed User
Unsubscribed User
8,947 Points

Perhaps my previous answer was a bit confusing. My second paragraph was meant as an example, not as something that should be part of an if statement in your code. Let's go back to the code in your initial question. The only line you need to change is:

self.fuel_remaining = (fuel_remaining - 0.125) * length

And let's focus on what is to the right of the equal to sign:

(fuel_remaining - 0.125) * length

Now, if we assume that you have 1 (litre) of fuel. We know that 0.125 litre of fuel is used each lap. So two laps should use 0.25 litres of fuel. Thus, after two laps you would have 1 - 0.25 = 0.75. Now, if we use this in your code:

self.fuel_remaining = (fuel_remaining - 0.125) * length

self.fuel_remaining = (1 - 0.125) * 2

self.fuel_remaining = 0.75 *2

self.fuel_remaining = 1.5

But that can't be right. You have more fuel than when you started!

However (and the right answer):

self.fuel_remaining = fuel_remaining - (0.125 * length)

self.fuel_remaining = 1 - (0.125 * 2)

self.fuel_remaining = 1 - 0.25

self.fuel_remaining = 0.75

Caleb Newell
Caleb Newell
12,562 Points

Thank you for explaining this.

Unsubscribed User
Unsubscribed User
8,947 Points
Unsubscribed User
Unsubscribed User
8,947 Points

(fuel_remaining - 0.125) * length

If fuel_remaining = 1 and length = 2, you will have more fuel remaining after two laps than before you ran the laps. Consider changing the above equation.

You need to multiply length with 0.125 and subtract the result from fuel_remaining.

Caleb Newell
Caleb Newell
12,562 Points

every thing else in my code still works, but i still do not understand the equation. A little more help would be thanked!

(by the way, does this look right?)

class RaceCar():    
    def __init__(self, color, fuel_remaining, laps=0, **kwargs):
        self.color = color
        self.laps = laps
        self.fuel_remaining = fuel_remaining

        for key, value in kwargs.items():
            setattr(self, key, value)

    def run_lap(self, length, fuel_remaining, **kwargs):
        if fuel_remaining == 1 and length == 2():
            length * 0.125 - fuel_remaining
Unsubscribed User
Unsubscribed User
8,947 Points
Unsubscribed User
Unsubscribed User
8,947 Points

As I said, go back to your initial code, and change the run_lap method by moving the parenthesis:

    def run_lap(self, length, **kwargs):
        self.fuel_remaining = fuel_remaining - (0.125 * length)
        laps = laps + 1
Caleb Newell
Caleb Newell
12,562 Points

Yep. I got it. Thanks for taking the time out of your schedule and helping me!

Unsubscribed User
Unsubscribed User
8,947 Points

No problem! If you don't already, I recommend testing the challenges (where possible) in an IDE such as MS Visual Studio Code or Atom. Being able to test different arguments helps a lot!

Kyle Bateman
Kyle Bateman
3,642 Points
Kyle Bateman
Kyle Bateman
3,642 Points

I seem to have the exact same code as what is shown in this community board, but I cannot get it to work. Can anyone help me?

class RaceCar:

def __init__(self, color, fuel_remaining, laps=0, **kwargs):
    self.color = color
    self.laps = laps
    self.fuel_remaining = fuel_remaining

    for key, value in kwargs.items():
        setattr(self, key, value)

def run_lap(self, length, **kwargs):       
    self.fuel_remaining = fuel_remaining - (0.125 * length)
    laps = laps + 1
Kyle Bateman
Kyle Bateman
3,642 Points

I figured it out...the last line was incorrect. Should have been:

self.laps = laps + 1

or

self.laps += 1