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Inventory Management

Welcome to Inventory Management on Exercism's Python Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

A dictionary is Python's primary mapping type that associates a hashable key with a value. The lookup by key is more efficient than searching through an array, but does require more memory.

Dict construction

Dictionaries can be created in various ways. Two simple options are the use the dict() class constructor or the dict literal declaration with key-value pairs.

Use the dict() constructor

>>> bear = dict(name="Black Bear", speed=40, land_animal=True)
{'name': 'Black Bear', 'speed': 40, 'land_animal': True}

Declare a dict literal

>>> whale = {"name": "Blue Whale", "speed": 35, "land_animal": False}
{'name': 'Blue Whale', 'speed': 35, 'land_animal': False}

With the dict literal declaration keep in mind that keys are of data types str and the colon : is used instead of an equal sign =.

Accessing values

You can access an item in a dictionary using the key of the value.

Using square brackets after the dict object

>>> bear["speed"]
40

Using .get()

>>> whale.get("name")
'Blue Whale'

Changing values

You can easily change a value of an item using its key.

>>> bear["name"] = "Grizzly Bear"
{'name': 'Grizzly Bear', 'speed': 40, 'land_animal': True}

>>> whale["speed"] = 25
{'name': 'Blue Whale', 'speed': 25, 'land_animal': False}

Deleting values using keys

You can delete an item from a dictionary using dict.pop(<key>). This will remove the (key, value) pair from the dictionary and return the value for use. dict.pop(<key>) accepts second argument, default that is returned if the key is not found (dict.pop(<key>, <default>)). Otherwise, a KeyError will be raised for any key that is missing.

>>> bear.pop("name")
'Grizzly Bear'
>>> bear.pop("name", "Unknown")
'Unknown'
>>> bear.pop("name")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'name'

Looping through a dictionary

Looping through a dictionary using for item in dict will iterate over the keys, but you can access the values by using square brackets.

>>> for key in bear:
>>>     (key, bear[key])
('name', 'Black Bear')
('speed', 40)
('land_animal', True)

Instructions

In this exercise, you will be managing an inventory system.

The inventory should be organized by the item name and it should keep track of the number of items available.

You will have to handle adding items to an inventory. Each time an item appears in a given list, increase the item's quantity by 1 in the inventory. Then, you will have to handle deleting items from an inventory.

To finish, you will have to implement a function which returns all the key-value pairs in an inventory as a list of tuples.

1. Create an inventory based on a list

Implement the create_inventory() function that creates an "inventory" from a list of items. It should return a dict containing each item name paired with their respective quantity.

>>> create_inventory(["coal", "wood", "wood", "diamond", "diamond", "diamond"])
{"coal":1, "wood":2, "diamond":3}

2. Add items from a list to an existing dictionary

Implement the add_items() function that adds a list of items to an inventory:

>>> add_items({"coal":1}, ["wood", "iron", "coal", "wood"])
{"coal":2, "wood":2, "iron":1}

3. Decrement items from the inventory

Implement the decrement_items(<items>) function that takes a list of items. The function should remove one from the available count in the inventory for each time an item appears on the list:

>>> decrement_items({"coal":3, "diamond":1, "iron":5}, ["diamond", "coal", "iron", "iron"])
{"coal":2, "diamond":0, "iron":3}

Item counts in the inventory should not fall below 0. If the number of times an item appears on the list exceeds the count available, the quantity listed for that item should remain at 0 and additional requests for removing counts should be ignored.

>>> decrement_items({"coal":2, "wood":1, "diamond":2}, ["coal", "coal", "wood", "wood", "diamond"])
{"coal":0, "wood":0, "diamond":1}

4. Remove an item entirely from the inventory

Implement the remove_item(<inventory>, <item>) function that removes an item and its count entirely from an inventory:

>>> remove_item({"coal":2, "wood":1, "diamond":2}, "coal")
{"wood":1, "diamond":2}

If the item is not found in the inventory, the function should return the original inventory unchanged.

>>> remove_item({"coal":2, "wood":1, "diamond":2}, "gold")
{"coal":2, "wood":1, "diamond":2}

5. Return the inventory content

Implement the list_inventory() function that takes an inventory and returns a list of (item, quantity) tuples. The list should only include the available items (with a quantity greater than zero):

>>> list_inventory({"coal":7, "wood":11, "diamond":2, "iron":7, "silver":0})
[('coal', 7), ('diamond', 2), ('iron', 7), ('wood', 11)]

Source

Created by

  • @j08k

Contributed to by

  • @valentin-p
  • @bethanyG
  • @mukeshgurpude
  • @kotp

My Solution