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Python Object-Oriented Python Inheritance Super!

Michael Sothan
Michael Sothan
8,048 Points
Posted by Michael Sothan
Michael Sothan
8,048 Points

how to sort a list built inside of a child class?

I don't understand why the self.slots list will not sort.

So, if my list was 

my_list = SortedInventory()

then I would have a list named "my_list". So, assuming there's no sort code,

my_list.add_item("cookie", "banana")

would give me a list like [cookie, banana] right? But, with the sort code, from my understanding, since python will automatically inherit the "list.sort" function, then the 

my_list.add_item("cookie", "banana")

method call should also run the "self.slots.sort()" code which (if we ran "print(my_list)") should output: [banana, cookie], no?

What am I missing? Do I need to put something in the "()" of "sort"? Or should the "list.sort()" code be placed inside of a separate method in the SortedInventory class?

inventory.py 
class Inventory:
    def __init__(self):
        self.slots = []

    def add_item(self, item):
        self.slots.append(item)

class SortedInventory(Inventory):
    def add_item(self, item):
        super().add_item(item)
        self.slots.append(item)
        self.slots.sort()

3 Answers

Josh Keenan
Josh Keenan
19,652 Points
Josh Keenan
Josh Keenan
19,652 Points

You're really close, look at the parent class, add_item already adds your item to the slots, you are doing it twice with your SortedInventory version of it too.

class Inventory:
    def __init__(self):
        self.slots = []

    def add_item(self, item):
        self.slots.append(item)

class SortedInventory(Inventory):
    def add_item(self, item):
        super().add_item(item)
        self.slots.sort()

Your code is adding the item, then adding it again, then sorting it, which is causing it to fail the challenge. You got this!

Michael Sothan
Michael Sothan
8,048 Points
Michael Sothan
Michael Sothan
8,048 Points

Thanks Josh. The second question in the challenge asked us to override the add_item method using super() which is why there is the extra add_item() in the child class. I passed that part, so I can't imagine that is the issue.

I tried it again using the following code (without the super() ):

class Inventory:
    def __init__(self):
        self.slots = []

class SortedInventory(Inventory):

    def add_item(self, item):
        self.slots.append(item)
        self.slots.sort()

But to no avail. Any idea?

Josh Keenan
Josh Keenan
19,652 Points
Josh Keenan
Josh Keenan
19,652 Points

Your problem is the extra append you have as I said in that comment,

class SortedInventory(Inventory):

    def add_item(self, item):
        self.slots.append(item)       # this line is why you are failing

You are adding it in the original method, super() is doing that for you, you need to remove it in the child class, readd the super, my code is what I used to pass it

Michael Sothan
Michael Sothan
8,048 Points
Michael Sothan
Michael Sothan
8,048 Points

Got it. Thanks Josh! I now see that I was misunderstanding the use of super(). I thought you had to re-write the code block from the parent class's method under your super() call. In this case:

self.slots.append(item)

I thought that seemed Highly redundant. Now I see that with the super() call in the child class you can use the code block from the parent class without rewriting anything! Thanks

Brian Davis
Brian Davis
1,628 Points
Brian Davis
Brian Davis
1,628 Points

That helps a lot. Is it just me, or is there being a lot left out in the lectures?