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Python

Posted by Luke Tate
Luke Tate
Courses Plus Student 2,256 Points

Why does my code return none, when appending a list within a Class?

class MuscleCar():
    list = ["4 wheels", "big engine", "2 doors", "high-speed", "4 seat"]
    "Class Attributes:"
    hp = 300
    spoiler = False
MuscleCar()
mCar = MuscleCar()
print(MuscleCar, mCar)
"Class Attributes:"
print(mCar.list)
print(mCar.list.append("exaust"))
mCar.list.extend([", exaust"])
print(mCar.hp)
print(MuscleCar.hp)

2 Answers

Jennifer Nordell
seal-mask
STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there, Luke Tate! The short story is that you're trying to print what is returned by the append method. But the append method just does something to the list and returns nothing. Much like a print statement itself prints something, but returns nothing. So if you did something like:

print(print("Hi"))

The output would be:

Hi
None

In the same way, you're appending something to the list and then printing out the result of running the append method. Instead, you'd want to update that list and then print out the list. Take a look:

class MuscleCar():
    list = ["4 wheels", "big engine", "2 doors", "high-speed", "4 seat"]
    "Class Attributes:"
    hp = 300
    spoiler = False
MuscleCar()
mCar = MuscleCar()
print(MuscleCar, mCar)  # This prints the object
"Class Attributes:"
print(mCar.list)  # This prints the the list stored in the class
print(mCar.list.append("exaust"))  # this will print None because the append method returns None
mCar.list.extend([", exaust"])
print(mCar.list)  # This is missing from your code. This prints the updated list
print(mCar.hp)
print(MuscleCar.hp)

Hope this helps! :sparkles:

Luke Tate
PLUS
Luke Tate
Courses Plus Student 2,256 Points
Luke Tate
Luke Tate
Courses Plus Student 2,256 Points

So you're saying 1) I can't merely use methods within each other, and 2) to print an updated list via using the append, or extend method first then printing out the list again?

Luke Tate
Luke Tate
Courses Plus Student 2,256 Points

Thanks! I get it now!