def get_num_items(self):
    num_items = 0
    for item in self.all_items_in_cart:
        num_items += RetailItem.get_units_in_inventory(item)
    return num_items
def get_num_items(self):
    num_items = 0
    for item in self.all_items_in_cart:
        num_items += RetailItem.get_units_in_inventory(item)
    return num_items