List to Dictionary Function Project - Automate the Boring Stuff Chapter 5

Question

This is the List to Dictionary Function for Fantasy Game Inventory project in Chapter 5.

The project is as follows:

Write a function named addToInventory(inventory, addedItems), where the inventory parameter is a dictionary representing the player’s inventory (like in the previous project) and the addedItems parameter is a list like dragonLoot. The addToInventory() function should return a dictionary that represents the updated inventory. Note that the addedItems list can contain multiples of the same item.

I believe I've filled the requirements but I wondered if I was doing something inefficiently.

My code:

def display_inventory(inventory):
 total_items = 0
 print ("Inventory:")
 for item in inventory.keys():
 print(str(inventory[item]) + ' ' + item)
 total_items += inventory[item]
 print("Total number of items: " + str(total_items))
def addToInventory(inventory, addedItems):
 for item in addedItems:
 if item in inventory:
 inventory[item] += 1
 else:
 inventory.setdefault(item, 1)
 
inv = {'rope': 1, 'torch': 6, 'gold coin': 42, 'dagger': 1, 'arrow': 12}
dragonLoot = ['gold coin', 'dagger', 'gold coin', 'gold coin', 'ruby', 'torch']
 
addToInventory(inv, dragonLoot)
display_inventory(inv)

• Zachary Vance: Including the example inv and dragonLoot made this much more readable, thanks

Answer 1

Put all code in functions. Even the usage-demo code. This is one of many bug-avoidance and testability-supporting habits that experienced programmers adopt.

Should the function return a new inventory or modify the current one? The text says we should "return a dictionary", but the suggested function name implies that we should modify/update the current inventory. This distinction is crucial in software engineering, and it's unfortunate that the book is so confused on this topic. Your code updates the current inventory (and returns None). Absent a compelling reason to do otherwise, one should prefer functions that return new data rather than functions that modify data they are given. There are many reasons for no-mutation as the default approach when writing functions, and I would encourage you to learn more about them.

If you need to count things, consider using a Counter. Python includes a dict-like data structure designed explicitly for counting things.

Displaying an inventory: take better advantage dict, print, and sum. Your code to display an inventory is overly complex. The print() function automatically converts its arguments to str, so you don't need to bother with that. It seems handier to iterate over both keys and values. And there's no need to add up the values yourself: let sum() do the work.

Pick a naming convention. Some of your code doesThis and some of it does_this. I see the latter more often in Python. Here's the code I ended up with.

import sys
from collections import Counter
def main():
 inv_initial = {'rope': 1, 'torch': 6, 'gold coin': 42, 'dagger': 1, 'arrow': 12}
 dragon_loot = ['gold coin', 'dagger', 'gold coin', 'gold coin', 'ruby', 'torch']
 inv_new = updated_inventory(inv_initial, dragon_loot)
 display_inventory(inv_initial, 'initial')
 display_inventory(inv_new, 'new')
def updated_inventory(inventory, added):
 c = Counter(inventory)
 c.update(added)
 return dict(c)
def display_inventory(inventory, label = ''):
 total = sum(inventory.values())
 print(f'Inventory: {label} (total: {total})')
 for item, n in inventory.items():
 print(f' {item}: {n}')
if __name__ == '__main__':
 main()