Dictionary values missing

Question

I am doing the very last exercise on http://automatetheboringstuff.com/chapter5/. For some reason I am not able to get the displayInventory(inv) function to return the correct values outside of the addToInventory() function.

Here is the code:

def displayInventory(inventory):
    print("Inventory:")
    item_total = 0
    for k, v in inventory.items():
        print(str(v) + ' ' + k)
        item_total += v
    print("Total number of items: " + str(item_total))

def addToInventory(inventory, addedItems):
    for k in addedItems:
        if k in inventory:
            inv[k] = inv[k] + 1
            print('You have ' + str(inv[k]) + ' ' + k + 's')
    else:
        print(k + ' is not in inventory')
        inventory.setdefault(k, 1)
print()
displayInventory(inv) #does work

inv = {'gold coin': 42, 'rope': 1}
displayInventory(inv)
print()
dragonLoot = ['gold coin', 'dagger', 'gold coin', 'gold coin', 'ruby']
inv = addToInventory(inv, dragonLoot)
print()
displayInventory(inv) #Doesn't work

I get the error: AttributeError: 'NoneType' object has no attribute 'items' It looks like the inv dictionary is empty. Why it is emptied and why the values are different outside of the function?

Answer 1

Your addToInventory() function returns None, because you don't have a specific return statement.

Since the function alters the dictionary in place, you should just not use the return value; remove the inv = part:

# ignore the return value; do not replace `inv` with it
addToInventory(inv, dragonLoot)