Set

A set in Python is unordered collection of unique elements. Unordered means it does not keep the order of the elements and unique means it does not allow duplicates.

Its mostly used when removing duplicates from list or performing quick membership tests (checking to see if some element belongs to both sets).

Lesson Overview

In this lesson we will cover:

• How to create set
• How to access elements of the set
• Adding or removing elements
• Set operations

Creating Set

Creating sets in Python is done with curly braces {} or its constructor set().

Python Sandbox

To create an empty set, we need to use set() function as using {} will create a new dictionary (which we will cover in the next lesson).

Accessing Elements

We cannot access elements of the set like we did with other data structures using index, but we can iterate over it with for loop or check if the item exists with in keyword :

Python SandboxView on Memory Graph ↗

Adding and Removing Elements

We can use .add() method to add a single element to set or use .update() method to add multiple elements.

Python SandboxView on Memory Graph ↗

Removing the elements can be done with .remove() method which raises KeyError if that element does not exist.

Python SandboxView on Memory Graph ↗

Set Operations

Sets support mathematical operations like union, intersection, and difference, making them useful for comparing collections.

Python Sandbox

📚Learn more about Python Sets

Explore Python sets deeper by visiting this [built-in: set] article from Real Python (especially the part about additional methods which come in handy when working with sets).

Remember you do not need to remember all the methods there are. Just read through them, to know they exist.

Exercise

Complete [TODO] Exercise 07 — WorkingTitle to practice sets.

Assignment

In this assigment our task is simple one. We need to track distinct unsold items so we can better prepare for the next day in our little shop.

1. Open main.py file we have been working on.
2. Define a set for all sold items (item[0] of element in order list) and define a set of all inventory items (item[0] of element in inventory list) - you can use set coprehension to do this in one line or use a for loop to iterate over each item in the lists.
3. Create a variable unsold_items and set its value to be sold_items substracted from all_inventory_items
4. Print out items that did not have a sale today.
5. Confirm the program works, commit and push to Github

What's Next

Now that we covered index based data structures, it's time to meet dictionary which is unique in its key-value approach and is probably most used data structure (besides lists).