How to iterate through instance of a parent class?

Question

I'm trying to iterate through a dictionary object initialized in a parent class, and append it to an instance in a child class. However, when I try to iterate through it, I receive...

TypeError: 'NoneType' object is not iterable

...when running for key in self.inv

class Inventory:
    '''Create inventory class'''
    def __init__(self, inv):
        self.inv = inv

 class Cart(Inventory):
    '''Customer shopping cart class'''
    def __init__(self, cart):
        self.cart = cart
        self.inv = super(Inventory).__init__()

    
    def scanning(self, inv):
        Inventory.displayInv(inv)
        print(vars(inv))
        scanned = 0
        while scanned != "pay":
            scanned = input("Input a barcode to scan or type 'pay' to pay: ")
            if scanned.isdigit():
                scanned = int(scanned)
            for key in self.inv:         #THIS IS WHERE THE ERROR OCCURS
                if key == scanned:
                    print(self.inv[key])
                    Cart.updateCart(self.cart, self.inv, key)
                    total_price, total_items = Cart.updateTotals(self)
                    Cart.displayCart(self, total_items, total_price)
                    break